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DynamicLoader: Don't use LibELF to do the initial relocations

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Using LibELF to do the initial relocations doesn't work when building
SerenityOS with Clang. We seem to be accessing a global symbol that
hasn't been relocated yet somewhere along the path to
ELF::DynamicObject::create().
This commit is contained in:
Gunnar Beutner 2021-07-06 10:17:11 +02:00 committed by Andreas Kling
parent c351b4ad0d
commit 4591c00328
Notes: sideshowbarker 2024-07-18 10:15:09 +09:00 
Author: https://github.com/gunnarbeutner
Commit: https://github.com/SerenityOS/serenity/commit/4591c003287
Pull-request: https://github.com/SerenityOS/serenity/pull/8487
1 changed files with 25 additions and 7 deletions
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32
Userland/DynamicLoader/main.cpp
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@ -46,17 +46,35 @@ static void perform_self_relocations(auxv_t* auxvp)
if (!dynamic_section_addr)
exit(1);
auto dynamic_object = ELF::DynamicObject::create({}, (VirtualAddress(base_address)), (VirtualAddress(dynamic_section_addr)));
FlatPtr relocation_section_addr = 0;
size_t relocation_table_size = 0;
size_t relocation_count = 0;
auto* dyns = reinterpret_cast<const ElfW(Dyn)*>(dynamic_section_addr);
for (unsigned i = 0;; ++i) {
auto& dyn = dyns[i];
if (dyn.d_tag == DT_NULL)
break;
if (dyn.d_tag == DT_REL || dyn.d_tag == DT_RELA)
relocation_section_addr = base_address + dyn.d_un.d_ptr;
else if (dyn.d_tag == DT_RELCOUNT || dyn.d_tag == DT_RELACOUNT)
relocation_count = dyn.d_un.d_val;
else if (dyn.d_tag == DT_RELSZ || dyn.d_tag == DT_RELASZ)
relocation_table_size = dyn.d_un.d_val;
}
if (!relocation_section_addr || !relocation_table_size || !relocation_count)
exit(1);
dynamic_object->relocation_section().for_each_relocation([base_address](auto& reloc) {
auto relocation_entry_size = relocation_table_size / relocation_count;
for (unsigned i = 0; i < relocation_count; ++i) {
size_t offset_in_section = i * relocation_entry_size;
auto* relocation = (ElfW(Rela)*)(relocation_section_addr + offset_in_section);
#if ARCH(I386)
VERIFY(reloc.type() == R_386_RELATIVE);
VERIFY(ELF32_R_TYPE(relocation->r_info) == R_386_RELATIVE);
#else
VERIFY(reloc.type() == R_X86_64_RELATIVE);
VERIFY(ELF64_R_TYPE(relocation->r_info) == R_X86_64_RELATIVE);
#endif
*(FlatPtr*)reloc.address().as_ptr() += base_address;
});
*(FlatPtr*)(base_address + relocation->r_offset) += base_address;
}
}
static void display_help()