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options/rtdl: Implement R_IRELATIVE relocation #951

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Feb 12, 2024
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options/rtdl: Implement R_IRELATIVE relocation #951

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c86c391
options/rtdl: Unify late relocation code
Qwinci Nov 19, 2023
ebe3623
options/rtdl: Implement R_IRELATIVE relocation
Qwinci Feb 4, 2024
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77 changes: 41 additions & 36 deletions options/rtdl/generic/linker.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -776,43 +776,46 @@ SharedObject::SharedObject(const char *name, const char *path,
frg::string<MemoryAllocator> { path, getAllocator() },
is_main_object, localScope, object_rts) {}

void processCopyRela(SharedObject *object, elf_rela *reloc) {
auto type = ELF_R_TYPE(reloc->r_info);
auto symbol_index = ELF_R_SYM(reloc->r_info);

if(type != R_COPY)
return;

uintptr_t rel_addr = object->baseAddress + reloc->r_offset;

auto symbol = (elf_sym *)(object->baseAddress + object->symbolTableOffset
+ symbol_index * sizeof(elf_sym));
ObjectSymbol r(object, symbol);
frg::optional<ObjectSymbol> p = Scope::resolveGlobalOrLocal(*globalScope, object->localScope, r.getString(), object->objectRts, Scope::resolveCopy);
__ensure(p);

memcpy((void *)rel_addr, (void *)p->virtualAddress(), symbol->st_size);
}

void processCopyRel(SharedObject *object, elf_rel *reloc) {
auto type = ELF_R_TYPE(reloc->r_info);
auto symbol_index = ELF_R_SYM(reloc->r_info);
void processLateRelocation(Relocation rel) {
// resolve the symbol if there is a symbol
frg::optional<ObjectSymbol> p;
if(rel.symbol_index()) {
auto symbol = (elf_sym *)(rel.object()->baseAddress + rel.object()->symbolTableOffset
+ rel.symbol_index() * sizeof(elf_sym));
ObjectSymbol r(rel.object(), symbol);

if(type != R_COPY)
return;
p = Scope::resolveGlobalOrLocal(*globalScope, rel.object()->localScope,
r.getString(), rel.object()->objectRts, Scope::resolveCopy);
}

uintptr_t rel_addr = object->baseAddress + reloc->r_offset;
switch(rel.type()) {
case R_COPY:
__ensure(p);
memcpy(rel.destination(), (void *)p->virtualAddress(), p->symbol()->st_size);
break;

auto symbol = (elf_sym *)(object->baseAddress + object->symbolTableOffset
+ symbol_index * sizeof(elf_sym));
ObjectSymbol r(object, symbol);
frg::optional<ObjectSymbol> p = Scope::resolveGlobalOrLocal(*globalScope, object->localScope, r.getString(), object->objectRts, Scope::resolveCopy);
__ensure(p);
// TODO: R_IRELATIVE also exists on other architectures but will likely need a different implementation.
#if defined(__x86_64__) || defined(__i386__)
case R_IRELATIVE: {
uintptr_t addr = rel.object()->baseAddress + rel.addend_rel();
auto* fn = reinterpret_cast<uintptr_t (*)()>(addr);
rel.relocate(fn());
} break;
#elif defined(__aarch64__)
case R_IRELATIVE: {
uintptr_t addr = rel.object()->baseAddress + rel.addend_rel();
auto* fn = reinterpret_cast<uintptr_t (*)(uint64_t)>(addr);
// TODO: the function should get passed AT_HWCAP value.
rel.relocate(fn(0));
} break;
#endif

memcpy((void *)rel_addr, (void *)p->virtualAddress(), symbol->st_size);
default:
break;
}
}

void processCopyRelocations(SharedObject *object) {
void processLateRelocations(SharedObject *object) {
frg::optional<uintptr_t> rel_offset;
frg::optional<size_t> rel_length;

Expand Down Expand Up @@ -847,12 +850,14 @@ void processCopyRelocations(SharedObject *object) {
if(rela_offset && rela_length) {
for(size_t offset = 0; offset < *rela_length; offset += sizeof(elf_rela)) {
auto reloc = (elf_rela *)(object->baseAddress + *rela_offset + offset);
processCopyRela(object, reloc);
auto r = Relocation(object, reloc);
processLateRelocation(r);
}
} else if(rel_offset && rel_length) {
for(size_t offset = 0; offset < *rel_length; offset += sizeof(elf_rel)) {
auto reloc = (elf_rel *)(object->baseAddress + *rel_offset + offset);
processCopyRel(object, reloc);
auto r = Relocation(object, reloc);
processLateRelocation(r);
}
}else{
__ensure(!rela_offset && !rela_length);
Expand Down Expand Up @@ -1315,7 +1320,7 @@ void Loader::linkObjects(SharedObject *root) {
if(object->dynamic == nullptr)
continue;

processCopyRelocations(object);
processLateRelocations(object);
}

for(auto object : _linkBfs) {
Expand Down Expand Up @@ -1476,8 +1481,8 @@ void Loader::_scheduleInit(SharedObject *object) {
}

void Loader::_processRelocations(Relocation &rel) {
// copy relocations have to be performed after all other relocations
if(rel.type() == R_COPY)
// copy and irelative relocations have to be performed after all other relocations
if(rel.type() == R_COPY || rel.type() == R_IRELATIVE)
return;

// resolve the symbol if there is a symbol
Expand Down
6 changes: 5 additions & 1 deletion options/rtdl/generic/linker.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -233,8 +233,12 @@ struct Relocation {
__builtin_unreachable();
}

void *destination() {
return reinterpret_cast<void *>(object_->baseAddress + offset_);
}

void relocate(elf_addr addr) {
auto ptr = reinterpret_cast<void *>(object_->baseAddress + offset_);
auto ptr = destination();
memcpy(ptr, &addr, sizeof(addr));
}

Expand Down
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