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LibELF: Support weak symbols when using BIND_NOW

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When using BIND_NOW (e.g. via -Wl,-z,now) we would fail to load ELF
images while doing relocations when we encounter a weak symbol. Instead
we should just patch the PLT entry with a null pointer.

This can be reproduced with:

$ cat test.cpp
int main()
{
    std::cout << "Hello World!" << std::endl;
}
$ g++ -o test -Wl,-z,now test.cpp
$ ./test
did not find symbol while doing relocations for library test: _ITM_RU1
This commit is contained in:
Gunnar Beutner 2021-05-31 11:39:00 +02:00 • committed by Linus Groh
parent 26cb64573c
commit 73b9cfac1b
1 changed files with 4 additions and 2 deletions
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6
Userland/Libraries/LibELF/DynamicObject.cpp
View file

@ -454,13 +454,15 @@ VirtualAddress DynamicObject::patch_plt_entry(u32 relocation_offset)
auto symbol = relocation.symbol(); auto symbol = relocation.symbol();
u8* relocation_address = relocation.address().as_ptr(); u8* relocation_address = relocation.address().as_ptr();
VirtualAddress symbol_location;
auto result = DynamicLoader::lookup_symbol(symbol); auto result = DynamicLoader::lookup_symbol(symbol);
if (!result.has_value()) { if (result.has_value()) {
symbol_location = result.value().address;
} else if (symbol.bind() != STB_WEAK) {
dbgln("did not find symbol while doing relocations for library {}: {}", m_filename, symbol.name()); dbgln("did not find symbol while doing relocations for library {}: {}", m_filename, symbol.name());
VERIFY_NOT_REACHED(); VERIFY_NOT_REACHED();
} }
auto symbol_location = result.value().address;
dbgln_if(DYNAMIC_LOAD_DEBUG, "DynamicLoader: Jump slot relocation: putting {} ({}) into PLT at {}", symbol.name(), symbol_location, (void*)relocation_address); dbgln_if(DYNAMIC_LOAD_DEBUG, "DynamicLoader: Jump slot relocation: putting {} ({}) into PLT at {}", symbol.name(), symbol_location, (void*)relocation_address);
*(FlatPtr*)relocation_address = symbol_location.get(); *(FlatPtr*)relocation_address = symbol_location.get();