Related
I'm still a bit new to c++ and I'm having trouble understanding what this piece of code is doing:
#include <net/sock.h>
BEGIN
{
printf("%-8s %-6s %-16s %-2s %-16s %-5s\n", "TIME", "PID", "COMM",
"IP", "RADDR", "RPORT");
}
kprobe:ip4_datagram_connect,
kprobe:ip6_datagram_connect
{
$sk = (struct sock *)arg0;
$sa = (struct sockaddr *)arg1;
if (($sa->sa_family == AF_INET || $sa->sa_family == AF_INET6) &&
$sk->sk_protocol == IPPROTO_UDP) {
time("%H:%M:%S ");
if ($sa->sa_family == AF_INET) {
$s = (struct sockaddr_in *)arg1;
$port = ($s->sin_port >> 8) |
(($s->sin_port << 8) & 0xff00);
printf("%-6d %-16s 4 %-16s %-5d\n", pid, comm,
ntop(AF_INET, $s->sin_addr.s_addr), $port);
} else {
$s6 = (struct sockaddr_in6 *)arg1;
$port = ($s6->sin6_port >> 8) |
(($s6->sin6_port << 8) & 0xff00);
printf("%-6d %-16s 6 %-16s %-5d\n", pid, comm,
ntop(AF_INET6, $s6->sin6_addr.in6_u.u6_addr8),
$port);
}
}
}
I think the "BEGIN" portion of this is defining a macro, but I'm not fully sure. What I'm really confused about is the
kprobe:ip4_datagram_connect,
kprobe:ip6_datagram_connect
{
What is this doing? It seems like a function declaration, but what does the single colon mean in this context? Is this some sort initialization list but for functions? Is this setting both ip4 and ip6 to that function?
Also, do the dollar sign variable names have any sort of significance? or are they just a valid way of declaring variables?
This is the code for udpconnect.bt from bcc tools. I'm try to convert it to python.
As mentioned in the comments, this is a script for bpftrace. You probably want to look at the reference guide for this tool.
The BEGIN block is run at the start of your program (just like with awk scripts, if you are familiar with it). In this case it is used to print the header row for an array to the console output.
Then the block:
kprobe:ip4_datagram_connect,
kprobe:ip6_datagram_connect
{
... defines instructions that will be translated to an eBPF program (with an intermediary step as LLVM intermediate representation), and attached to one or several hooks in the Linux kernel. In the current case, the kprobe:... define the hooks: The program will run as a kprobe function for the functions ip4_datagram_connect and its IPv6 counterpart in the kernel. In other words, it will run each time the kernel enters those functions.
On a quick look, I think the program is supposed to print, each time a UDP flow starts, the time, PID and name of the process opening the socket, the IP address, remote address and remote port. The first if checks that the packet is (IPv4 or IPv6) and UDP, the if/else below splits the two cases IPv4/IPv6.
It is my first attempt to implement recursion with CUDA. The goal is to extract all the combinations from a set of chars "12345" using the power of CUDA to parallelize dynamically the task. Here is my kernel:
__device__ char route[31] = { "_________________________"};
__device__ char init[6] = { "12345" };
__global__ void Recursive(int depth) {
// up to depth 6
if (depth == 5) return;
// newroute = route - idx
int x = depth * 6;
printf("%s\n", route);
int o = 0;
int newlen = 0;
for (int i = 0; i<6; ++i)
{
if (i != threadIdx.x)
{
route[i+x-o] = init[i];
newlen++;
}
else
{
o = 1;
}
}
Recursive<<<1,newlen>>>(depth + 1);
}
__global__ void RecursiveCount() {
Recursive <<<1,5>>>(0);
}
The idea is to exclude 1 item (the item corresponding to the threadIdx) in each different thread. In each recursive call, using the variable depth, it works over a different base (variable x) on the route device variable.
I expect the kernel prompts something like:
2345_____________________
1345_____________________
1245_____________________
1234_____________________
2345_345_________________
2345_245_________________
2345_234_________________
2345_345__45_____________
2345_345__35_____________
2345_345__34_____________
..
2345_245__45_____________
..
But it prompts ...
·_____________
·_____________
·_____________
·_____________
·_____________
·2345
·2345
·2345
·2345
...
What I´m doing wrong?
What I´m doing wrong?
I may not articulate every problem with your code, but these items should get you a lot closer.
I recommend providing a complete example. In my view it is basically required by Stack Overflow, see item 1 here, note use of the word "must". Your example is missing any host code, including the original kernel call. It's only a few extra lines of code, why not include it? Sure, in this case, I can deduce what the call must have been, but why not just include it? Anyway, based on the output you indicated, it seems fairly evident the launch configuration of the host launch would have to be <<<1,1>>>.
This doesn't seem to be logical to me:
I expect the kernel prompts something like:
2345_____________________
The very first thing your kernel does is print out the route variable, before making any changes to it, so I would expect _____________________. However we can "fix" this by moving the printout to the end of the kernel.
You may be confused about what a __device__ variable is. It is a global variable, and there is only one copy of it. Therefore, when you modify it in your kernel code, every thread, in every kernel, is attempting to modify the same global variable, at the same time. That cannot possibly have orderly results, in any thread-parallel environment. I chose to "fix" this by making a local copy for each thread to work on.
You have an off-by-1 error, as well as an extent error in this loop:
for (int i = 0; i<6; ++i)
The off-by-1 error is due to the fact that you are iterating over 6 possible items (that is, i can reach a value of 5) but there are only 5 items in your init variable (the 6th item being a null terminator. The correct indexing starts out over 0-4 (with one of those being skipped). On subsequent iteration depths, its necessary to reduce this indexing extent by 1. Note that I've chosen to fix the first error here by increasing the length of init. There are other ways to fix, of course. My method inserts an extra _ between depths in the result.
You assume that at each iteration depth, the correct choice of items is the same, and in the same order, i.e. init. However this is not the case. At each depth, the choices of items must be selected not from the unchanging init variable, but from the choices passed from previous depth. Therefore we need a local, per-thread copy of init also.
A few other comments about CUDA Dynamic Parallelism (CDP). When passing pointers to data from one kernel scope to a child scope, local space pointers cannot be used. Therefore I allocate for the local copy of route from the heap, so it can be passed to child kernels. init can be deduced from route, so we can use an ordinary local variable for myinit.
You're going to quickly hit some dynamic parallelism (and perhaps memory) limits here if you continue this. I believe the total number of kernel launches for this is 5^5, which is 3125 (I'm doing this quickly, I may be mistaken). CDP has a pending launch limit of 2000 kernels by default. We're not hitting this here according to what I see, but you'll run into that sooner or later if you increase the depth or width of this operation. Furthermore, in-kernel allocations from the device heap are by default limited to 8KB. I don't seem to be hitting that limit, but probably I am, so my design should probably be modified to fix that.
Finally, in-kernel printf output is limited to the size of a particular buffer. If this technique is not already hitting that limit, it will soon if you increase the width or depth.
Here is a worked example, attempting to address the various items above. I'm not claiming it is defect free, but I think the output is closer to your expectations. Note that due to character limits on SO answers, I've truncated/excerpted some of the output.
$ cat t1639.cu
#include <stdio.h>
__device__ char route[31] = { "_________________________"};
__device__ char init[7] = { "12345_" };
__global__ void Recursive(int depth, const char *oroute) {
char *nroute = (char *)malloc(31);
char myinit[7];
if (depth == 0) memcpy(myinit, init, 6);
else memcpy(myinit, oroute+(depth-1)*6, 6);
myinit[6] = 0;
if (nroute == NULL) {printf("oops\n"); return;}
memcpy(nroute, oroute, 30);
nroute[30] = 0;
// up to depth 6
if (depth == 5) return;
// newroute = route - idx
int x = depth * 6;
//printf("%s\n", nroute);
int o = 0;
int newlen = 0;
for (int i = 0; i<(6-depth); ++i)
{
if (i != threadIdx.x)
{
nroute[i+x-o] = myinit[i];
newlen++;
}
else
{
o = 1;
}
}
printf("%s\n", nroute);
Recursive<<<1,newlen>>>(depth + 1, nroute);
}
__global__ void RecursiveCount() {
Recursive <<<1,5>>>(0, route);
}
int main(){
RecursiveCount<<<1,1>>>();
cudaDeviceSynchronize();
}
$ nvcc -o t1639 t1639.cu -rdc=true -lcudadevrt -arch=sm_70
$ cuda-memcheck ./t1639
========= CUDA-MEMCHECK
2345_____________________
1345_____________________
1245_____________________
1235_____________________
1234_____________________
2345__345________________
2345__245________________
2345__235________________
2345__234________________
2345__2345_______________
2345__345___45___________
2345__345___35___________
2345__345___34___________
2345__345___345__________
2345__345___45____5______
2345__345___45____4______
2345__345___45____45_____
2345__345___45____5______
2345__345___45____5_____5
2345__345___45____4______
2345__345___45____4_____4
2345__345___45____45____5
2345__345___45____45____4
2345__345___35____5______
2345__345___35____3______
2345__345___35____35_____
2345__345___35____5______
2345__345___35____5_____5
2345__345___35____3______
2345__345___35____3_____3
2345__345___35____35____5
2345__345___35____35____3
2345__345___34____4______
2345__345___34____3______
2345__345___34____34_____
2345__345___34____4______
2345__345___34____4_____4
2345__345___34____3______
2345__345___34____3_____3
2345__345___34____34____4
2345__345___34____34____3
2345__345___345___45_____
2345__345___345___35_____
2345__345___345___34_____
2345__345___345___45____5
2345__345___345___45____4
2345__345___345___35____5
2345__345___345___35____3
2345__345___345___34____4
2345__345___345___34____3
2345__245___45___________
2345__245___25___________
2345__245___24___________
2345__245___245__________
2345__245___45____5______
2345__245___45____4______
2345__245___45____45_____
2345__245___45____5______
2345__245___45____5_____5
2345__245___45____4______
2345__245___45____4_____4
2345__245___45____45____5
2345__245___45____45____4
2345__245___25____5______
2345__245___25____2______
2345__245___25____25_____
2345__245___25____5______
2345__245___25____5_____5
2345__245___25____2______
2345__245___25____2_____2
2345__245___25____25____5
2345__245___25____25____2
2345__245___24____4______
2345__245___24____2______
2345__245___24____24_____
2345__245___24____4______
2345__245___24____4_____4
2345__245___24____2______
2345__245___24____2_____2
2345__245___24____24____4
2345__245___24____24____2
2345__245___245___45_____
2345__245___245___25_____
2345__245___245___24_____
2345__245___245___45____5
2345__245___245___45____4
2345__245___245___25____5
2345__245___245___25____2
2345__245___245___24____4
2345__245___245___24____2
2345__235___35___________
2345__235___25___________
2345__235___23___________
2345__235___235__________
2345__235___35____5______
2345__235___35____3______
2345__235___35____35_____
2345__235___35____5______
2345__235___35____5_____5
2345__235___35____3______
2345__235___35____3_____3
2345__235___35____35____5
2345__235___35____35____3
2345__235___25____5______
2345__235___25____2______
2345__235___25____25_____
2345__235___25____5______
2345__235___25____5_____5
2345__235___25____2______
2345__235___25____2_____2
2345__235___25____25____5
2345__235___25____25____2
2345__235___23____3______
2345__235___23____2______
2345__235___23____23_____
2345__235___23____3______
2345__235___23____3_____3
2345__235___23____2______
2345__235___23____2_____2
2345__235___23____23____3
2345__235___23____23____2
2345__235___235___35_____
2345__235___235___25_____
2345__235___235___23_____
2345__235___235___35____5
2345__235___235___35____3
2345__235___235___25____5
2345__235___235___25____2
2345__235___235___23____3
2345__235___235___23____2
2345__234___34___________
2345__234___24___________
2345__234___23___________
2345__234___234__________
2345__234___34____4______
2345__234___34____3______
2345__234___34____34_____
2345__234___34____4______
2345__234___34____4_____4
2345__234___34____3______
2345__234___34____3_____3
2345__234___34____34____4
2345__234___34____34____3
2345__234___24____4______
2345__234___24____2______
2345__234___24____24_____
2345__234___24____4______
2345__234___24____4_____4
2345__234___24____2______
2345__234___24____2_____2
2345__234___24____24____4
2345__234___24____24____2
2345__234___23____3______
2345__234___23____2______
2345__234___23____23_____
2345__234___23____3______
2345__234___23____3_____3
2345__234___23____2______
2345__234___23____2_____2
2345__234___23____23____3
2345__234___23____23____2
2345__234___234___34_____
2345__234___234___24_____
2345__234___234___23_____
2345__234___234___34____4
2345__234___234___34____3
2345__234___234___24____4
2345__234___234___24____2
2345__234___234___23____3
2345__234___234___23____2
2345__2345__345__________
2345__2345__245__________
2345__2345__235__________
2345__2345__234__________
2345__2345__345___45_____
2345__2345__345___35_____
2345__2345__345___34_____
2345__2345__345___45____5
2345__2345__345___45____4
2345__2345__345___35____5
2345__2345__345___35____3
2345__2345__345___34____4
2345__2345__345___34____3
2345__2345__245___45_____
2345__2345__245___25_____
2345__2345__245___24_____
2345__2345__245___45____5
2345__2345__245___45____4
2345__2345__245___25____5
2345__2345__245___25____2
2345__2345__245___24____4
2345__2345__245___24____2
2345__2345__235___35_____
2345__2345__235___25_____
2345__2345__235___23_____
2345__2345__235___35____5
2345__2345__235___35____3
2345__2345__235___25____5
2345__2345__235___25____2
2345__2345__235___23____3
2345__2345__235___23____2
2345__2345__234___34_____
2345__2345__234___24_____
2345__2345__234___23_____
2345__2345__234___34____4
2345__2345__234___34____3
2345__2345__234___24____4
2345__2345__234___24____2
2345__2345__234___23____3
2345__2345__234___23____2
1345__345________________
1345__145________________
1345__135________________
1345__134________________
1345__1345_______________
1345__345___45___________
1345__345___35___________
1345__345___34___________
1345__345___345__________
1345__345___45____5______
1345__345___45____4______
1345__345___45____45_____
1345__345___45____5______
1345__345___45____5_____5
1345__345___45____4______
1345__345___45____4_____4
1345__345___45____45____5
1345__345___45____45____4
1345__345___35____5______
1345__345___35____3______
1345__345___35____35_____
1345__345___35____5______
1345__345___35____5_____5
1345__345___35____3______
1345__345___35____3_____3
1345__345___35____35____5
1345__345___35____35____3
1345__345___34____4______
1345__345___34____3______
1345__345___34____34_____
1345__345___34____4______
1345__345___34____4_____4
1345__345___34____3______
1345__345___34____3_____3
1345__345___34____34____4
1345__345___34____34____3
1345__345___345___45_____
1345__345___345___35_____
1345__345___345___34_____
1345__345___345___45____5
1345__345___345___45____4
1345__345___345___35____5
1345__345___345___35____3
1345__345___345___34____4
1345__345___345___34____3
1345__145___45___________
1345__145___15___________
1345__145___14___________
1345__145___145__________
1345__145___45____5______
1345__145___45____4______
1345__145___45____45_____
1345__145___45____5______
1345__145___45____5_____5
1345__145___45____4______
1345__145___45____4_____4
1345__145___45____45____5
1345__145___45____45____4
1345__145___15____5______
1345__145___15____1______
1345__145___15____15_____
1345__145___15____5______
1345__145___15____5_____5
1345__145___15____1______
1345__145___15____1_____1
1345__145___15____15____5
1345__145___15____15____1
1345__145___14____4______
1345__145___14____1______
1345__145___14____14_____
1345__145___14____4______
1345__145___14____4_____4
1345__145___14____1______
1345__145___14____1_____1
1345__145___14____14____4
1345__145___14____14____1
1345__145___145___45_____
1345__145___145___15_____
1345__145___145___14_____
1345__145___145___45____5
1345__145___145___45____4
1345__145___145___15____5
1345__145___145___15____1
1345__145___145___14____4
1345__145___145___14____1
1345__135___35___________
1345__135___15___________
1345__135___13___________
1345__135___135__________
1345__135___35____5______
1345__135___35____3______
1345__135___35____35_____
1345__135___35____5______
1345__135___35____5_____5
1345__135___35____3______
1345__135___35____3_____3
1345__135___35____35____5
1345__135___35____35____3
1345__135___15____5______
1345__135___15____1______
1345__135___15____15_____
1345__135___15____5______
1345__135___15____5_____5
1345__135___15____1______
1345__135___15____1_____1
1345__135___15____15____5
1345__135___15____15____1
1345__135___13____3______
1345__135___13____1______
1345__135___13____13_____
1345__135___13____3______
1345__135___13____3_____3
1345__135___13____1______
1345__135___13____1_____1
1345__135___13____13____3
1345__135___13____13____1
1345__135___135___35_____
1345__135___135___15_____
1345__135___135___13_____
1345__135___135___35____5
1345__135___135___35____3
1345__135___135___15____5
1345__135___135___15____1
1345__135___135___13____3
1345__135___135___13____1
1345__134___34___________
1345__134___14___________
1345__134___13___________
1345__134___134__________
1345__134___34____4______
1345__134___34____3______
1345__134___34____34_____
1345__134___34____4______
1345__134___34____4_____4
1345__134___34____3______
1345__134___34____3_____3
1345__134___34____34____4
1345__134___34____34____3
1345__134___14____4______
1345__134___14____1______
1345__134___14____14_____
1345__134___14____4______
1345__134___14____4_____4
1345__134___14____1______
1345__134___14____1_____1
1345__134___14____14____4
1345__134___14____14____1
1345__134___13____3______
1345__134___13____1______
1345__134___13____13_____
1345__134___13____3______
1345__134___13____3_____3
1345__134___13____1______
1345__134___13____1_____1
1345__134___13____13____3
1345__134___13____13____1
1345__134___134___34_____
1345__134___134___14_____
1345__134___134___13_____
1345__134___134___34____4
1345__134___134___34____3
1345__134___134___14____4
1345__134___134___14____1
1345__134___134___13____3
1345__134___134___13____1
1345__1345__345__________
1345__1345__145__________
1345__1345__135__________
1345__1345__134__________
1345__1345__345___45_____
1345__1345__345___35_____
1345__1345__345___34_____
1345__1345__345___45____5
1345__1345__345___45____4
1345__1345__345___35____5
1345__1345__345___35____3
1345__1345__345___34____4
1345__1345__345___34____3
1345__1345__145___45_____
1345__1345__145___15_____
1345__1345__145___14_____
1345__1345__145___45____5
1345__1345__145___45____4
1345__1345__145___15____5
1345__1345__145___15____1
1345__1345__145___14____4
1345__1345__145___14____1
1345__1345__135___35_____
1345__1345__135___15_____
1345__1345__135___13_____
1345__1345__135___35____5
1345__1345__135___35____3
1345__1345__135___15____5
1345__1345__135___15____1
1345__1345__135___13____3
1345__1345__135___13____1
1345__1345__134___34_____
1345__1345__134___14_____
1345__1345__134___13_____
1345__1345__134___34____4
1345__1345__134___34____3
1345__1345__134___14____4
1345__1345__134___14____1
1345__1345__134___13____3
1345__1345__134___13____1
1245__245________________
1245__145________________
1245__125________________
1245__124________________
1245__1245_______________
1245__245___45___________
1245__245___25___________
1245__245___24___________
1245__245___245__________
1245__245___45____5______
1245__245___45____4______
1245__245___45____45_____
1245__245___45____5______
1245__245___45____5_____5
1245__245___45____4______
1245__245___45____4_____4
1245__245___45____45____5
1245__245___45____45____4
1245__245___25____5______
1245__245___25____2______
1245__245___25____25_____
1245__245___25____5______
1245__245___25____5_____5
1245__245___25____2______
1245__245___25____2_____2
1245__245___25____25____5
1245__245___25____25____2
1245__245___24____4______
1245__245___24____2______
1245__245___24____24_____
1245__245___24____4______
1245__245___24____4_____4
1245__245___24____2______
1245__245___24____2_____2
1245__245___24____24____4
1245__245___24____24____2
1245__245___245___45_____
1245__245___245___25_____
1245__245___245___24_____
1245__245___245___45____5
1245__245___245___45____4
1245__245___245___25____5
1245__245___245___25____2
1245__245___245___24____4
1245__245___245___24____2
1245__145___45___________
1245__145___15___________
1245__145___14___________
1245__145___145__________
1245__145___45____5______
1245__145___45____4______
1245__145___45____45_____
1245__145___45____5______
1245__145___45____5_____5
1245__145___45____4______
...
1235__1235__235___25_____
1235__1235__235___23_____
1235__1235__235___35____5
1235__1235__235___35____3
1235__1235__235___25____5
1235__1235__235___25____2
1235__1235__235___23____3
1235__1235__235___23____2
1235__1235__135___35_____
1235__1235__135___15_____
1235__1235__135___13_____
1235__1235__135___35____5
1235__1235__135___35____3
1235__1235__135___15____5
1235__1235__135___15____1
1235__1235__135___13____3
1235__1235__135___13____1
1235__1235__125___25_____
1235__1235__125___15_____
1235__1235__125___12_____
1235__1235__125___25____5
1235__1235__125___25____2
1235__1235__125___15____5
1235__1235__125___15____1
1235__1235__125___12____2
1235__1235__125___12____1
1235__1235__123___23_____
1235__1235__123___13_____
1235__1235__123___12_____
1235__1235__123___23____3
1235__1235__123___23____2
1235__1235__123___13____3
1235__1235__123___13____1
1235__1235__123___12____2
1235__1235__123___12____1
1234__234________________
1234__134________________
1234__124________________
1234__123________________
1234__1234_______________
1234__234___34___________
1234__234___24___________
1234__234___23___________
1234__234___234__________
1234__234___34____4______
1234__234___34____3______
1234__234___34____34_____
1234__234___34____4______
1234__234___34____4_____4
1234__234___34____3______
1234__234___34____3_____3
1234__234___34____34____4
1234__234___34____34____3
1234__234___24____4______
1234__234___24____2______
1234__234___24____24_____
1234__234___24____4______
1234__234___24____4_____4
1234__234___24____2______
1234__234___24____2_____2
1234__234___24____24____4
1234__234___24____24____2
1234__234___23____3______
1234__234___23____2______
1234__234___23____23_____
1234__234___23____3______
1234__234___23____3_____3
1234__234___23____2______
1234__234___23____2_____2
1234__234___23____23____3
1234__234___23____23____2
1234__234___234___34_____
1234__234___234___24_____
1234__234___234___23_____
1234__234___234___34____4
1234__234___234___34____3
1234__234___234___24____4
1234__234___234___24____2
1234__234___234___23____3
1234__234___234___23____2
1234__134___34___________
1234__134___14___________
1234__134___13___________
1234__134___134__________
1234__134___34____4______
1234__134___34____3______
1234__134___34____34_____
1234__134___34____4______
1234__134___34____4_____4
1234__134___34____3______
1234__134___34____3_____3
1234__134___34____34____4
1234__134___34____34____3
1234__134___14____4______
1234__134___14____1______
1234__134___14____14_____
1234__134___14____4______
1234__134___14____4_____4
1234__134___14____1______
1234__134___14____1_____1
1234__134___14____14____4
1234__134___14____14____1
1234__134___13____3______
1234__134___13____1______
1234__134___13____13_____
1234__134___13____3______
1234__134___13____3_____3
1234__134___13____1______
1234__134___13____1_____1
1234__134___13____13____3
1234__134___13____13____1
1234__134___134___34_____
1234__134___134___14_____
1234__134___134___13_____
1234__134___134___34____4
1234__134___134___34____3
1234__134___134___14____4
1234__134___134___14____1
1234__134___134___13____3
1234__134___134___13____1
1234__124___24___________
1234__124___14___________
1234__124___12___________
1234__124___124__________
1234__124___24____4______
1234__124___24____2______
1234__124___24____24_____
1234__124___24____4______
1234__124___24____4_____4
1234__124___24____2______
1234__124___24____2_____2
1234__124___24____24____4
1234__124___24____24____2
1234__124___14____4______
1234__124___14____1______
1234__124___14____14_____
1234__124___14____4______
1234__124___14____4_____4
1234__124___14____1______
1234__124___14____1_____1
1234__124___14____14____4
1234__124___14____14____1
1234__124___12____2______
1234__124___12____1______
1234__124___12____12_____
1234__124___12____2______
1234__124___12____2_____2
1234__124___12____1______
1234__124___12____1_____1
1234__124___12____12____2
1234__124___12____12____1
1234__124___124___24_____
1234__124___124___14_____
1234__124___124___12_____
1234__124___124___24____4
1234__124___124___24____2
1234__124___124___14____4
1234__124___124___14____1
1234__124___124___12____2
1234__124___124___12____1
1234__123___23___________
1234__123___13___________
1234__123___12___________
1234__123___123__________
1234__123___23____3______
1234__123___23____2______
1234__123___23____23_____
1234__123___23____3______
1234__123___23____3_____3
1234__123___23____2______
1234__123___23____2_____2
1234__123___23____23____3
1234__123___23____23____2
1234__123___13____3______
1234__123___13____1______
1234__123___13____13_____
1234__123___13____3______
1234__123___13____3_____3
1234__123___13____1______
1234__123___13____1_____1
1234__123___13____13____3
1234__123___13____13____1
1234__123___12____2______
1234__123___12____1______
1234__123___12____12_____
1234__123___12____2______
1234__123___12____2_____2
1234__123___12____1______
1234__123___12____1_____1
1234__123___12____12____2
1234__123___12____12____1
1234__123___123___23_____
1234__123___123___13_____
1234__123___123___12_____
1234__123___123___23____3
1234__123___123___23____2
1234__123___123___13____3
1234__123___123___13____1
1234__123___123___12____2
1234__123___123___12____1
1234__1234__234__________
1234__1234__134__________
1234__1234__124__________
1234__1234__123__________
1234__1234__234___34_____
1234__1234__234___24_____
1234__1234__234___23_____
1234__1234__234___34____4
1234__1234__234___34____3
1234__1234__234___24____4
1234__1234__234___24____2
1234__1234__234___23____3
1234__1234__234___23____2
1234__1234__134___34_____
1234__1234__134___14_____
1234__1234__134___13_____
1234__1234__134___34____4
1234__1234__134___34____3
1234__1234__134___14____4
1234__1234__134___14____1
1234__1234__134___13____3
1234__1234__134___13____1
1234__1234__124___24_____
1234__1234__124___14_____
1234__1234__124___12_____
1234__1234__124___24____4
1234__1234__124___24____2
1234__1234__124___14____4
1234__1234__124___14____1
1234__1234__124___12____2
1234__1234__124___12____1
1234__1234__123___23_____
1234__1234__123___13_____
1234__1234__123___12_____
1234__1234__123___23____3
1234__1234__123___23____2
1234__1234__123___13____3
1234__1234__123___13____1
1234__1234__123___12____2
1234__1234__123___12____1
========= ERROR SUMMARY: 0 errors
$
The answer given by Robert Crovella is correct at the 5th point, the mistake was in the using of init in every recursive call, but I want to clarify something that can be useful for other beginners with CUDA.
I used this variable because when I tried to launch a child kernel passing a local variable I always got the exception: Error: a pointer to local memory cannot be passed to a launch as an argument.
As I´m C# expert developer I´m not used to using pointers (Ref does the low-level-work for that) so I thought there was no way to do it in CUDA/c programming.
As Robert shows in its code it is possible copying the pointer with memalloc for using it as a referable argument.
Here is a kernel simplified as an example of deep recursion.
__device__ char init[6] = { "12345" };
__global__ void Recursive(int depth, const char* route) {
// up to depth 6
if (depth == 5) return;
//declaration for a referable argument (point 6)
char* newroute = (char*)malloc(6);
memcpy(newroute, route, 5);
int o = 0;
int newlen = 0;
for (int i = 0; i < (6 - depth); ++i)
{
if (i != threadIdx.x)
{
newroute[i - o] = route[i];
newlen++;
}
else
{
o = 1;
}
}
printf("%s\n", newroute);
Recursive <<<1, newlen>>>(depth + 1, newroute);
}
__global__ void RecursiveCount() {
Recursive <<<1, 5>>>(0, init);
}
I don't add the main call because I´m using ManagedCUDA for C# but as Robert says it can be figured-out how the call RecursiveCount is.
About ending arrays of char with /0 ... sorry but I don't know exactly what is the benefit; this code works fine without them.
I am getting into Vulkan and stumbled on my first problem. When trying to create a debug report callback (validation layers and debug extensions are available on my intel hd vulkan driver, at least it says so), it fails telling me vkCreateDebugReportCallbackEXT is an unresolved symbol. When trying to get the function pointer it fails telling me vkCreateDebugReportCallbackEXT is already defined.
Which it is, in the Vulkan header. I could set VK_NO_PROTOTYPES but then I would have to load everything by hand. Is there a way around this? Just using a different name for the function pointer won't work, since I am using Vulkan-Hpp and it uses vkCreateDebugReportCallbackEXT as it is.
Is this a driver bug, telling me debug extensions are available, but there are not?
Btw, I am using VS2015.
Thanks for any help
That's normal. vulkan.h defines them as a global functions. But the loader commands obviously return function pointer.
Normally you would just use a different name you like. But I like to have the canonical names too...
I solve it by defining the function myself (using the declaration from vulkan.h) which in turn calls the loaded pointer:
VKAPI_ATTR VkResult VKAPI_CALL vkCommandEXT( /*...*/ ){
return fpCommandEXT( /*...*/ );
}
(Shameless self-promotion) Like so:
https://github.com/krOoze/Hello_Triangle/blob/8227220/ErrorHandling.h#L181
I make the command to self-load on its first use — if you don't like that, in older commit I had more conventional loader:
https://github.com/krOoze/Hello_Triangle/blob/699ab57/HelloTriangle.cpp#L731
PS:
Khronos themselves just added loader code that illustrates that nicely:
https://github.com/KhronosGroup/Vulkan-Docs/blob/1.0/src/ext_loader/vulkan_ext.c
If you handle multiple VkInstances or VkDevices the loaded functions have to be dispatched to the correct instance or device. For example, I do that (likely inefficiently) here:
https://github.com/krOoze/Hello_Triangle/blob/a691de5/ExtensionLoader.h
I had same issue, couldn't find solution so i solved it this way
(might be wrong, but i just want to share in case it will help somebody):
struct DebugDispatch {
//KHRONOS
PFN_vkCreateDebugReportCallbackEXT vkCreateDebugReportCallbackEXT = 0;
PFN_vkDestroyDebugReportCallbackEXT vkDestroyDebugReportCallbackEXT = 0;
//LUNARG
PFN_vkCreateDebugUtilsMessengerEXT vkCreateDebugUtilsMessengerEXT = 0;
PFN_vkDestroyDebugUtilsMessengerEXT vkDestroyDebugUtilsMessengerEXT = 0;
}
VKAPI_ATTR vk::Bool32 VKAPI_CALL debugReportCallback(...){...}
VKAPI_ATTR vk::Bool32 VKAPI_CALL debugUtilsMessengerCallback(...){...}
enum class ValidationFlagsBits : unsigned int {
NONE = 0,
KHRONOS = 1,
LUNARG = 1 << 1
};
typedef vk::Flags<ValidationFlagsBits> ValidationFlags;
void Example(){
...
vk::Instance instance;
instance = vk::createInstance(...);
DebugDispatch debug_dispatch;
vk::DebugReportCallbackEXT debug_report_callback;
vk::DebugUtilsMessengerEXT debug_utils_messenger;
if(validation_flags & ValidationFlagsBits::KHRONOS){
debug_dispatch.vkCreateDebugReportCallbackEXT =
(PFN_vkCreateDebugReportCallbackEXT)instance.getProcAddr("vkCreateDebugReportCallbackEXT");
debug_dispatch.vkDestroyDebugReportCallbackEXT =
(PFN_vkDestroyDebugReportCallbackEXT)instance.getProcAddr("vkDestroyDebugReportCallbackEXT");
vk::DebugUtilsMessengerCreateInfoEXT create_info{};
create_info.messageSeverity = ...;
create_info.messageType = ...;
create_info.pfnUserCallback = reinterpret_cast<PFN_vkDebugUtilsMessengerCallbackEXT>(&debugUtilsMessengerCallback);
debug_utils_messenger = instance.createDebugUtilsMessengerEXT(create_info, nullptr, debug_dispatch);
}
if(validation_flags & ValidationFlagsBits::LUNARG){
debug_dispatch.vkCreateDebugUtilsMessengerEXT =
(PFN_vkCreateDebugUtilsMessengerEXT)instance.getProcAddr("vkCreateDebugUtilsMessengerEXT");
debug_dispatch.vkDestroyDebugUtilsMessengerEXT =
(PFN_vkDestroyDebugUtilsMessengerEXT)instance.getProcAddr("vkDestroyDebugUtilsMessengerEXT");
vk::DebugReportCallbackCreateInfoEXT create_info{};
create_info.flags = ...;
create_info.pfnCallback = reinterpret_cast<PFN_vkDebugReportCallbackEXT>(&debugReportCallback);
debug_report_callback = instance.createDebugReportCallbackEXT(create_info, nullptr, debug_dispatch);
}
...
if(validation_flags & ValidationFlagsBits::KHRONOS){
instance.destroyDebugUtilsMessengerEXT(debug_utils_messenger, nullptr, debug_dispatch);
}
if(validation_flags & ValidationFlagsBits::LUNARG){
instance.destroyDebugReportCallbackEXT(debug_report_callback, nullptr, debug_dispatch);
}
instance.destroy();
}
I am trying to interface with a Devantech digital compass found here -
http://www.acroname.com/robotics/parts/R117-COMPASS.html
I am using a i2c-usb converter to plug it into my laptop -
http://www.robot-electronics.co.uk/htm/usb_i2c_tech.htm
First of all, I do not know much about electrical engineering. I have a good idea of the bare basics, but after that I get lost.
I am trying to follow this tutorial -
https://xgoat.com/wp/2007/11/11/using-i2c-from-userspace-in-linux/
However I get stuck at the very beginning when I try to set the device address.
if( ioctl( fd, I2C_SLAVE, ADDRESS ) < 0 )
{
fprintf( stderr, "Failed to set slave address: %m\n" );
return 2;
}
returns "Failed to set slave address: Invalid argument"
I originally thought the address should be 0xC0 because a sentence in the manual for the compass reads "First send a start bit, the module address (0xC0)..." but that did not work.
Now I have a loop that just goes from 1 to 100 and tries each one for the address, but they all fail. The loop is -
for(int i=0x0;i<0x100;i++) {
if( ioctl( fd, I2C_SLAVE, i ) < 0 )
fprintf( stderr, "Failed to set slave address for address %i: %m\n", i );
}
I'm not sure what else to try. Right now, I just want to set the address so I can start attempting to read and write. Since the converter is what is actually connected to the pc, should I be using the address for that? And if so, where can I find it on that link with the information for it? If someone has an idea of what I could try or what is wrong that would be great.
EDIT:
Okay I have the code like this now -
#define ADDRESS 0x55
int fd = open("/dev/i2c-0", O_RDWR);
if (fd < 0) {
printf("\n<0, %m", errno);
return -1;
}
if( ioctl( fd, I2C_SLAVE, ADDRESS ) < 0 ) {
fprintf( stderr, "Failed to set slave address: %m\n" );
return 2;
}
if( i2c_smbus_write_byte( fd, 0xAA ) < 0 )
fprintf( stderr, "Failed to write 0xAA to I2C device: %m\n" );
It will set the address, but it won't write anything. Whenever I try to write to it, I get -
Failed to write 0xAA to I2C device: No such device or address
Why are your trying to send 0xAA to the device ?
To my understanding this is not a register for it (for the CMPS03, the only command is register 15 and its usage is not common: change the I2C address, factory reset, ...).
And 0x55 seems definitively not the address of the device ... 0xC0 should be the write one.
Could be that /dev/i2c-0 has not been created properly / is not correct?
How did you get /dev/ic2-0 created ?
I'm studying dynamic/static scope with deep/shallow binding and running code manually to see how these different scopes/bindings actually work. I read the theory and googled some example exercises and the ones I found are very simple (like this one which was very helpful with dynamic scoping) But I'm having trouble understanding how static scope works.
Here I post an exercise I did to check if I got the right solution:
considering the following program written in pseudocode:
int u = 42;
int v = 69;
int w = 17;
proc add( z:int )
u := v + u + z
proc bar( fun:proc )
int u := w;
fun(v)
proc foo( x:int, w:int )
int v := x;
bar(add)
main
foo(u,13)
print(u)
end;
What is printed to screen
a) using static scope? answer=180
b) using dynamic scope and deep binding? answer=69 (sum for u = 126 but it's foo's local v, right?)
c) using dynamic scope and shallow binding? answer=69 (sum for u = 101 but it's foo's local v, right?)
PS: I'm trying to practice doing some exercises like this if you know where I can find these types of problems (preferable with solutions) please give the link, thanks!
Your answer for lexical (static) scope is correct. Your answers for dynamic scope are wrong, but if I'm reading your explanations right, it's because you got confused between u and v, rather than because of any real misunderstanding about how deep and shallow binding work. (I'm assuming that your u/v confusion was just accidental, and not due to a strange confusion about values vs. references in the call to foo.)
a) using static scope? answer=180
Correct.
b) using dynamic scope and deep binding? answer=69 (sum for u = 126 but it's foo's local v, right?)
Your parenthetical explanation is right, but your answer is wrong: u is indeed set to 126, and foo indeed localizes v, but since main prints u, not v, the answer is 126.
c) using dynamic scope and shallow binding? answer=69 (sum for u = 101 but it's foo's local v, right?)
The sum for u is actually 97 (42+13+42), but since bar localizes u, the answer is 42. (Your parenthetical explanation is wrong for this one — you seem to have used the global variable w, which is 17, in interpreting the statement int u := w in the definition of bar; but that statement actually refers to foo's local variable w, its second parameter, which is 13. But that doesn't actually affect the answer. Your answer is wrong for this one only because main prints u, not v.)
For lexical scope, it's pretty easy to check your answers by translating the pseudo-code into a language with lexical scope. Likewise dynamic scope with shallow binding. (In fact, if you use Perl, you can test both ways almost at once, since it supports both; just use my for lexical scope, then do a find-and-replace to change it to local for dynamic scope. But even if you use, say, JavaScript for lexical scope and Bash for dynamic scope, it should be quick to test both.)
Dynamic scope with deep binding is much trickier, since few widely-deployed languages support it. If you use Perl, you can implement it manually by using a hash (an associative array) that maps from variable-names to scalar-refs, and passing this hash from function to function. Everywhere that the pseudocode declares a local variable, you save the existing scalar-reference in a Perl lexical variable, then put the new mapping in the hash; and at the end of the function, you restore the original scalar-reference. To support the binding, you create a wrapper function that creates a copy of the hash, and passes that to its wrapped function. Here is a dynamically-scoped, deeply-binding implementation of your program in Perl, using that approach:
#!/usr/bin/perl -w
use warnings;
use strict;
# Create a new scalar, initialize it to the specified value,
# and return a reference to it:
sub new_scalar($)
{ return \(shift); }
# Bind the specified procedure to the specified environment:
sub bind_proc(\%$)
{
my $V = { %{+shift} };
my $f = shift;
return sub { $f->($V, #_); };
}
my $V = {};
$V->{u} = new_scalar 42; # int u := 42
$V->{v} = new_scalar 69; # int v := 69
$V->{w} = new_scalar 17; # int w := 17
sub add(\%$)
{
my $V = shift;
my $z = $V->{z}; # save existing z
$V->{z} = new_scalar shift; # create & initialize new z
${$V->{u}} = ${$V->{v}} + ${$V->{u}} + ${$V->{z}};
$V->{z} = $z; # restore old z
}
sub bar(\%$)
{
my $V = shift;
my $fun = shift;
my $u = $V->{u}; # save existing u
$V->{u} = new_scalar ${$V->{w}}; # create & initialize new u
$fun->(${$V->{v}});
$V->{u} = $u; # restore old u
}
sub foo(\%$$)
{
my $V = shift;
my $x = $V->{x}; # save existing x
$V->{x} = new_scalar shift; # create & initialize new x
my $w = $V->{w}; # save existing w
$V->{w} = new_scalar shift; # create & initialize new w
my $v = $V->{v}; # save existing v
$V->{v} = new_scalar ${$V->{x}}; # create & initialize new v
bar %$V, bind_proc %$V, \&add;
$V->{v} = $v; # restore old v
$V->{w} = $w; # restore old w
$V->{x} = $x; # restore old x
}
foo %$V, ${$V->{u}}, 13;
print "${$V->{u}}\n";
__END__
and indeed it prints 126. It's obviously messy and error-prone, but it also really helps you understand what's going on, so for educational purposes I think it's worth it!
Simple and deep binding are Lisp interpreter viewpoints of the pseudocode. Scoping is just pointer arithmetic. Dynamic scope and static scope are the same if there are no free variables.
Static scope relies on a pointer to memory. Empty environments hold no symbol to value associations; denoted by word "End." Each time the interpreter reads an assignment, it makes space for association between a symbol and value.
The environment pointer is updated to point to the last association constructed.
env = End
env = [u,42] -> End
env = [v,69] -> [u,42] -> End
env = [w,17] -> [v,69] -> [u,42] -> End
Let me record this environment memory location as AAA. In my Lisp interpreter, when meeting a procedure, we take the environment pointer and put it our pocket.
env = [add,[closure,(lambda(z)(setq u (+ v u z)),*AAA*]]->[w,17]->[v,69]->[u,42]->End.
That's pretty much all there is until the procedure add is called. Interestingly, if add is never called, you just cost yourself a pointer.
Suppose the program calls add(8). OK, let's roll. The environment AAA is made current. Environment is ->[w,17]->[v,69]->[u,42]->End.
Procedure parameters of add are added to the front of the environment. The environment becomes [z,8]->[w,17]->[v,69]->[u,42]->End.
Now the procedure body of add is executed. Free variable v will have value 69. Free variable u will have value 42. z will have the value 8.
u := v + u + z
u will be assigned the value of 69 + 42 + 8 becomeing 119.
The environment will reflect this: [z,8]->[w,17]->[v,69]->[u,119]->End.
Assume procedure add has completed its task. Now the environment gets restored to its previous value.
env = [add,[closure,(lambda(z)(setq u (+ v u z)),*AAA*]]->[w,17]->[v,69]->[u,119]->End.
Notice how the procedure add has had a side effect of changing the value of free variable u. Awesome!
Regarding dynamic scoping: it just ensures closure leaves out dynamic symbols, thereby avoiding being captured and becoming dynamic.
Then put assignment to dynamic at top of code. If dynamic is same as parameter name, it gets masked by parameter value passed in.
Suppose I had a dynamic variable called z. When I called add(8), z would have been set to 8 regardless of what I wanted. That's probably why dynamic variables have longer names.
Rumour has it that dynamic variables are useful for things like backtracking, using let Lisp constructs.
Static binding, also known as lexical scope, refers to the scoping mechanism found in most modern languages.
In "lexical scope", the final value for u is neither 180 or 119, which are wrong answers.
The correct answer is u=101.
Please see standard Perl code below to understand why.
use strict;
use warnings;
my $u = 42;
my $v = 69;
my $w = 17;
sub add {
my $z = shift;
$u = $v + $u + $z;
}
sub bar {
my $fun = shift;
$u = $w;
$fun->($v);
}
sub foo {
my ($x, $w) = #_;
$v = $x;
bar( \&add );
}
foo($u,13);
print "u: $u\n";
Regarding shallow binding versus deep binding, both mechanisms date from the former LISP era.
Both mechanisms are meant to achieve dynamic binding (versus lexical scope binding) and therefore they produce identical results !
The differences between shallow binding and deep binding do not reside in semantics, which are identical, but in the implementation of dynamic binding.
With deep binding, variable bindings are set within a stack as "varname => varvalue" pairs.
The value of a given variable is retrieved from traversing the stack from top to bottom until a binding for the given variable is found.
Updating the variable consists in finding the binding in the stack and updating the associated value.
On entering a subroutine, a new binding for each actual parameter is pushed onto the stack, potentially hiding an older binding which is therefore no longer accessible wrt the retrieving mechanism described above (that stops at the 1st retrieved binding).
On leaving the subroutine, bindings for these parameters are simply popped from the binding stack, thus re-enabling access to the former bindings.
Please see the the code below for a Perl implementation of deep-binding dynamic scope.
use strict;
use warnings;
use utf8;
##
# Dynamic-scope deep-binding implementation
my #stack = ();
sub bindv {
my ($varname, $varval);
unshift #stack, [ $varname => $varval ]
while ($varname, $varval) = splice #_, 0, 2;
return $varval;
}
sub unbindv {
my $n = shift || 1;
shift #stack while $n-- > 0;
}
sub getv {
my $varname = shift;
for (my $i=0; $i < #stack; $i++) {
return $stack[$i][1]
if $varname eq $stack[$i][0];
}
return undef;
}
sub setv {
my ($varname, $varval) = #_;
for (my $i=0; $i < #stack; $i++) {
return $stack[$i][1] = $varval
if $varname eq $stack[$i][0];
}
return bindv($varname, $varval);
}
##
# EXERCICE
bindv( u => 42,
v => 69,
w => 17,
);
sub add {
bindv(z => shift);
setv(u => getv('v')
+ getv('u')
+ getv('z')
);
unbindv();
}
sub bar {
bindv(fun => shift);
setv(u => getv('w'));
getv('fun')->(getv('v'));
unbindv();
}
sub foo {
bindv(x => shift,
w => shift,
);
setv(v => getv('x'));
bar( \&add );
unbindv(2);
}
foo( getv('u'), 13);
print "u: ", getv('u'), "\n";
The result is u=97
Nevertheless, this constant traversal of the binding stack is costly : 0(n) complexity !
Shallow binding brings a wonderful O(1) enhanced performance over the previous implementation !
Shallow binding is improving the former mechanism by assigning each variable its own "cell", storing the value of the variable within the cell.
The value of a given variable is simply retrieved from the variable's
cell (using a hash table on variable names, we achieve a
0(1) complexity for accessing variable's values!)
Updating the variable's value is simply storing the value into the
variable's cell.
Creating a new binding (entering subs) works by pushing the old value
of the variable (a previous binding) onto the stack, and storing the
new local value in the value cell.
Eliminating a binding (leaving subs) works by popping the old value
off the stack into the variable's value cell.
Please see the the code below for a trivial Perl implementation of shallow-binding dynamic scope.
use strict;
use warnings;
our $u = 42;
our $v = 69;
our $w = 17;
our $z;
our $fun;
our $x;
sub add {
local $z = shift;
$u = $v + $u + $z;
}
sub bar {
local $fun = shift;
$u = $w;
$fun->($v);
}
sub foo {
local $x = shift;
local $w = shift;
$v = $x;
bar( \&add );
}
foo($u,13);
print "u: $u\n";
As you shall see, the result is still u=97
As a conclusion, remember two things :
shallow binding produces the same results as deep binding, but runs faster, since there is never a need to search for a binding.
The problem is not shallow binding versus deep binding versus
static binding BUT lexical scope versus dynamic scope (implemented either with deep or shallow binding).