I have problem with Binary open file in c++/cli. How to open the whole file and save the contest of the file to the array ^.
A typical method for reading the contest [sic] of a Binarny [sic] file is to:
1. Determine the length of the file.
2. Allocate dynamic memory for the file.
3. Block read the file, in binary mode, into memory.
Some operating systems may have a memory map capability. This allows a file to be treated as an array. The OS is in charge of reading the file into memory. It may read the entire file, or it may read pages as necessary (on demand).
See std::ifstream::read, std::ifstream::seekg and std::ifstream::tellg.
I am basically following up on core dump note section. I didn't post that question but I am trying to do the same thing: write a program to create core dump file from scratch; except that I am trying to do that for a custom, single threaded firmware running on embedded ARM processor.
I am also referring to Google coredumper source to understand how corefiles are usually created. So far I have successfully created a core file with a PT_NOTE and a PT_LOAD program headers which is read by GDB.
Note that, I am trying to create this core file for a custom firmware and this is not Linux environment. My question is regarding PT_LOAD program headers. From what I understood, I just need to create as many PT_LOAD program headers as active threads (for which core needs to be created) with headers representing each thread's memory mappings. Since my firmware is single threaded, I created only one PT_LOAD program header with memory mapping being address values on stack.
When I load up ELF image of the firmware with this newly created core file, GDB prints registers accurately with "info reg". GDB also identifies PC (program counter) value and displays the symbol accurately. It, however, cannot display remaining frames from stack ("bt" doesn't work). It complains that it "Cannot access memory at address (SP+4)".
I've already provided firmware's stack mappings in the core file and GDB should have been able to read at address (SP+4). Note that, I can examine the value at (SP+4) with "x 0x(SP+4)".
Can anyone tell me what am I missing here?
Thanks
I figured this out. Apparently, contents of the PT_LOAD program header - stack mappings - were not complete. The problem was that it needed entire mapping of the one thread that is running. After I included contents of entire CPU SRAM, GDB "bt" and all other commands worked just fine.
Also, from what I understood, the executable has address to all variables and core file has run-time values for those variables. So if any of the symbols are memory (RAM) resident then a separate PT_LOAD program header with RAM mapping should be added. After that GDB should be able to print runtime value of those variable accurately. Without the mapping, the value of the variable would be 0 (as shown by GDB).
I need to find the size of a directory (and its sub-directories). I can do this by iterating through the directory tree and summing up the file sizes etc. There are many examples on the internet but it's a somewhat tedious and slow process, particularly when looking at exceptionally large directory structures.
I notice that Apple's Finder application can instantly display a directory size for any given directory. This implies that the operating system is maintaining this information in real time. However, I've been unable to determine how to access this information. Does anyone know where this information is stored and if it can be retrieved by an Objective-C application?
IIRC Finder iterates too. In the old days, it used to use FSGetCatalogInfo (an old File Manager call) to do this quickly. I think there's a newer POSIX call for that these days that's the fastest, lowest-level API for this, especially if you're not interested in all the other info besides the size and really need blazing speed over easily maintainable code.
That said, if it is cached somewhere in a publicly accessible place, it is probably Spotlight. Have you checked whether the spotlight info for a folder includes its size?
PS - One important thing to remember when determining the size of a file: Mac files can have two "forks", the data fork, and the resource fork (where e.g. Finder keeps the info if you override a particular file to open with another application than the default for its file type, and custom icons assigned to files). So make sure you add up both forks' sizes, or your measurements will be off.
I've been reading ELF standard here. From what I understand, each ELF contains ELF header, program headers (why more than one?) and section headers. Can anyone please explain:
How are ELF files generated? is it the compiler responsibility?
What are sections and why do we need them?
What are program headers and why do we need them?
Inside program headers, what's the meaning of the fields p_vaddr and p_paddr?
Does each section have it's own section header?
Alternatively, does any one have a link to a more friendly documenation of ELF?
How are ELF files generated? is it the compiler responsibility?
They can be generated by a compiler, an assembler, or any other tool that can generate them. Even your own program you wrote for generating ELF files ;) They're just streams of bytes after all, so they can be generated by just writing bytes into a file in binary mode. You can do that too.
What are sections and why do we need them?
ELF files are subdivided into sections. Sections are the smallest continuous regions in the file. You can think of them as pages in an organizer, each with its own name and type that describes what does it contain inside. Linkers use this information to combine different parts of the program coming from different modules into one executable file or a library, by merging sections of the same type (gluing pages together, if you will).
In executable files, sections are optional, but they're usually there to describe what's in the file and where does it begin, and how much bytes does it take.
What are program headers and why do we need them?
They're mostly for making executable files. In order to run a program, sections aren't enough, because you have to specify not only what's there in the file, but also where should it be loaded into memory in the running process. Program headers are just for that purpose: they describe segments, which are regions of memory in the running process, with different access privileges & stuff.
Each program header describes one segment. It tells the loader where should it load a certain region in the file into memory and what permissions should it set for that region (e.g. should it be allowed to execute code from it? should it be writable or just for reading?)
Segments can be further subdivided into sections. For example, if you have to specify that your code segment is further subdivided into code and static read-only strings for the messages the program displays. Or that your data segment is subdivided into funky data and hardcore data :J It's for you to decide.
In executable files, sections are optional, but it's nice to have them, because they describe what's in the file and allow for dumping selected parts of it (e.g. with the objdump tool). Sometimes they are needed, though, for storing dynamic linking information, symbol tables, debugging information, stuff like that.
Inside program headers, what's the meaning of the fields p_vaddr and p_paddr?
Those are the addresses at which the data in the file will be loaded. They map the contents of the file into their corresponding memory locations. The first one is a virtual address, the second one is physical address.
Physical addresses are the "raw" memory addresses. On modern operating systems, those are no longer used in the userland. Instead, userland programs use virtual addresses. The operating system deceives the userland program that it is alone in memory, and that the entire address space is available for it. Under the hood, the operating system maps those virtual addresses to physical ones in the actual memory, and it does it transparently to the program.
Of course, not every address in the virtual address space is available at the same time. There are limitations imposed by the actual physical memory available. So the operating system just maps the memory for the segments the program actually uses (here's where the "segments" part from the ELF file's program headers comes into play). If the process tries to access some unmapped memory, the operating system steps in and says, "sorry, chap, this memory doesn't belong to you". (The program can address it, but it cannot access it.)
Does each section have it's own section header?
Yes. If it doesn't have an entry in the Section Headers Table, it's not a section :q Because they only way to tell if some part of the file is a section, is by looking in to the Section Headers Table which tells you what sections are defined in the file and where you can find them.
You can think of the Section Headers Table as a table of contents in a book. Without the table of contents, there aren't any chapters after all, because they're not listed anywhere. The book may have headings, but the content is not subdivided into logical chapters that can be found through the table of contents. Same goes with sections in ELF files: there can be some regions of data, but you can't tell without the "table of contents" which is the SHT.
This link includes a better explaination.
How are ELF files generated? is it the compiler responsibility?*
It is architecture dependent.
What are sections and why do we need them?
Different section have different information such as code, initialized data, uninitialized data etc. These information will be used by the compiler and linker.
What are program headers and why do we need them?
Program headers are used by the operating system when it loads the executable. These headers contains information about the segments (contiguous memory block with some permissions) such as which parts needs to be loaded, interpreter infor etc.
Inside program headers, what's the meaning of the fields p_vaddr and p_paddr?
In general virtual address and the physical address are same. But could be different depends on the system.
Does each section have it's own section header?
yes. Each section have a section header entry at section header table.
This is the best documentation I've found: http://www.skyfree.org/linux/references/ELF_Format.pdf
Each section has only one section header, but there can be section headers without sections
2 - There are many different sections, ex: relocation section recoeds many infomation for relocation symbol. I use the infomation to load a elf object and run/relocate the object.
Antoher example: debug section records debug information, gdb use the data for showing debug message.
Symbol section records symbol information.
3 - programming header used by loader, loader loads a elf execute file by looking up programming header.
OK, I'm working on a project right now and I need to create a graphic library.
The game I'm experimenting with is an RPG; this project is expected to contain many big graphic files to use and I would prefer not to load everything into memory at once, like I've done before with other smaller projects.
So, does anyone have experience with libraries such as this one? Here's what I've came up with:
Have graphic library files and paths in an XML file
Each entry in the XML file would be designated "PERMANENT" or "TEMPORARY", with perm. being that once loaded it stays in memory and won't be cleared (like menu-graphics)
The library that the XML file loads into would have a CLEAR command, that clears out all non-PERMANENT graphics
I have experience throwing everything into memory at startup, and with running the program running with the assumption that all necessary graphics are currently in memory. Are there any other considerations I might need to think about?
Ideally everything would be temporary and you would have a sensible evict function that chooses the right objects to victimize (based on access patterns) when your program decides it needs more memory.
There'll be some minimum amount of RAM your game needs to run, otherwise stuff will be constantly swapping, but this approach does mean you're not dumping objects marked TEMPORARY that you will just need to reload next frame because you happen to be using it currently.