All data structures that the file format defines follow the
"natural" size and alignment guidelines for the relevant class.
If necessary, data structures contain explicit padding to ensure
4-byte alignment for 4-byte objects, to force structure sizes to
a multiple of 4, and so on.
But since aligment is implementation defined I imagine that is not a good
pratice suppose that the structures are allways packed.
For example, the following (pseudocode) can falls in some systems/compilers:
unsigned char e_ident[EI_NIDENT]; // Supposing that sizeof(unsigned char) == sizeof(uint8_t)
Elf32_Ehdr *ehdr;
// First read the e_ident
fread(e_ident, EI_NIDENT, 1, file_ptr);
// Now read the ELF header
if(e_ident[EI_CLASS] == ELFCLASS32){
ehdr = malloc(sizeof(Elf32_Ehdr));
memcpy(ehdr->e_ident, e_ident, EI_NIDENT);
fread(&(ehdr->e_type), sizeof(uint8_t), sizeof(Elf32_Ehdr) - (size_t)EI_NIDENT, file_ptr);
}
On negative answer for the main question, there is some portable way to ensure that elf.h structures are packed?
NOTE: I'm using the elf.h from musl.
