Format of 64 bit symbol table entry in ELF - elf

Question

So I am trying to learn about the ELF by taking a close look how everything relates and can't understand why the symbol table entries are the size they are.
When I run readelf -W -S tiny.o I get:
Section Headers:
[Nr] Name Type Address Off Size ES Flg Lk Inf Al
[ 0] NULL 0000000000000000 000000 000000 00 0 0 0
[ 1] .bss NOBITS 0000000000000000 000200 000001 00 WA 0 0 4
[ 2] .text PROGBITS 0000000000000000 000200 00002a 00 AX 0 0 16
[ 3] .shstrtab STRTAB 0000000000000000 000230 000031 00 0 0 1
[ 4] .symtab SYMTAB 0000000000000000 000270 000090 18 5 5 4
[ 5] .strtab STRTAB 0000000000000000 000300 000015 00 0 0 1
[ 6] .rela.text RELA 0000000000000000 000320 000030 18 4 2 4
Which shows the symbol table having 0x18 or 24 bytes per entry and a total size of (0x300-0x270) or 0x90 giving us 6 entries.
This matches with what readelf -W -s tiny.o says:
Symbol table '.symtab' contains 6 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND
1: 0000000000000000 0 FILE LOCAL DEFAULT ABS tiny.asm
2: 0000000000000000 0 SECTION LOCAL DEFAULT 1
3: 0000000000000000 0 SECTION LOCAL DEFAULT 2
4: 0000000000000000 0 NOTYPE LOCAL DEFAULT 1 str
5: 0000000000000000 0 NOTYPE GLOBAL DEFAULT 2 _start
So clearly the 24 bytes size is correct, but that would correspond to a 32 bit table entry as decribed in this 32 bit spec.
Given that I am on a 64 bit system and the ELF file is 64 bit I would expect the entry to be as decribed in this 64 bit spec.
Upon looking at a hex dump of the file, I found that the layout of the fields in the file seems to be according to this 64 bit pattern.
So then why is the ELF file seemingly using undersized symbol table entries despite using the 64 bit layout and being a 64 bit file?

Answer 1

So then why is the ELF file seemingly using undersized symbol table entries
What makes you believe they are undersized?
In Elf64_Sym, we have:
int st_name
char st_info
char st_other
short st_shndx
<--- 8 bytes
long st_value
<--- 8 bytes
long st_size
<--- 8 bytes.
That's 24 bytes total, exactly as you'd expect.
To convince yourself that everything is in order, compile this program:
#include <elf.h>
#include <stdio.h>
int main()
{
Elf64_Sym s64;
Elf32_Sym s32;
printf("%zu %zu\n", sizeof(s32), sizeof(s64));
return 0;
}
Running it produces 16 24. You can also run it under GDB, and look at offsets of various fields, e.g.
(gdb) p (char*)&s64.st_value - (char*)&s64
$1 = 8
(gdb) p (char*)&s64.st_size - (char*)&s64
$2 = 16