获取ELF文件信息

Question

ok... so im suppose to write a program that prints all of the sections name in an elf file using only mmap (thats not important...)

so what i did so far is this - maped the file into the stat structure = map_start = mmap(0, fd_stat.st_size, PROT_READ | PROT_WRITE , MAP_SHARED, fd, 0)) <0 )

casted it into the write format from the starting point i got = header = (Elf32_Ehdr *) map_start;

gotten the section header offset from the file = secoff = header->e_shoff;

now - i know i need to go to the map_start+secoff location - that will give me the section table, and the sh_name will give me an index for the string table...

how to i go to the sting table? how is it represented? how do i use it? and is the value in sh_name the index in the string table (if it is represented as an array) , or an offset..

anyway - lets say i want to print the first two section's name - how do i do it givven the code i wrote above help please?

Answer 1

header = (Elf32_Ehdr *) map_start;
secoff = header->e_shoff;

This is probably wrong. Unless the Elf32_Ehdr structure is explicitly declared __attribute__((packed)) , the compiler will eventually insert padding between the members of the structure, so sizeof(Elf32_Ehdr) != (the actual size of an ELF header section) . Why not simply use the libelf accessor functions instead?

Update: if you're not allowed to use accessor functions, you'll have to do something like this:

Elf32_Ehdr hdr;
memcpy(&hdr.e_ident, map_start + 0, EI_NIDENT);
memcpy(&hdr.e.type, map_start + 0 + sizeof(Elf32_half), sizeof(Elf32_Half));

et cetera.