implement dl_iterate_phdr

[X512]

This is hrev53903.

dl_iterate_phdr is required for Mesa graphics drivers.

Required declarations are already present at ​https://git.haiku-os.org/haiku/tree/headers/compatibility/bsd/sys/link_elf.h.

[return_0e]

But dl_iterate_phdr isn't part of the POSIX standard. If we do end up implementing this, We probably would need to place the implementation under src/libs/bsd rather than in libroot.

[waddlesplash]

The dl_iterate_phdr() function allows an application to inquire at run time to find out which shared objects it has loaded.

I think you can rather easily implement this using Haiku's get_next_image_info. Indeed, it sounds like a good candidate to put into libbsd.

Musl's implementation, for reference: ​https://github.com/rofl0r/musl/blob/master/src/ldso/dl_iterate_phdr.c

[X512]

Also needed for LLVM libunwind. It is used to get unwind tables from ELF program header table (PT_GNU_EH_FRAME).

[X512]

I think you can rather easily implement this using Haiku's get_next_image_info.

No, it can't. dl_iterate_phdr allows go get image base and ELF program header table.

[X512]

runtime_loader currently don't save ELF header and program header table in ​image_t. image_t should be changed or dl_iterate_phdr implementation should read ELF file on each call.

Also image_t have no meaningful image base. It use regions that can be loaded at arbitrary addresses, possibly in different order than described in program header table. So formula addr == info->dlpi_addr + info->dlpi_phdr[x].p_vaddr; described in ​documentation may not work.