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LibC+LibELF: Pass information from linker via magic lookup

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This works by defining a set of weak symbols in dynamic linker whose
value would be provided by it. This has the same effect as preloading
library that magically knows right addresses of functions shared between
dynamic linker and LibC.

We were previously passing the same information by rewriting values
based on hardcoded library name, so the new approach seems a little
nicer to me.
This commit is contained in:
Dan Klishch 2024-01-20 16:20:42 -05:00 • committed by Andrew Kaster
parent a17041fe7f
commit 982799f7a0
6 changed files with 59 additions and 71 deletions
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8
Userland/Libraries/LibC/dlfcn.cpp
View file

@ -11,10 +11,10 @@
#include <string.h>
// These are filled in by the dynamic loader.
DlCloseFunction __dlclose;
DlOpenFunction __dlopen;
DlSymFunction __dlsym;
DlAddrFunction __dladdr;
[[gnu::weak]] DlCloseFunction __dlclose;
[[gnu::weak]] DlOpenFunction __dlopen;
[[gnu::weak]] DlSymFunction __dlsym;
[[gnu::weak]] DlAddrFunction __dladdr;
// FIXME: use thread_local and a String once TLS works
#ifdef NO_TLS

4
Userland/Libraries/LibC/libcinit.cpp
View file

@ -17,8 +17,8 @@ int errno_storage;
#else
__thread int errno_storage;
#endif
char** environ;
bool __environ_is_malloced;
[[gnu::weak]] char** environ;
bool __environ_is_malloced = false;
bool __stdio_is_initialized;
void* __auxiliary_vector;

2
Userland/Libraries/LibC/link.cpp
View file

@ -12,7 +12,7 @@ extern "C" {
using DlIteratePhdrCallbackFunction = int (*)(struct dl_phdr_info*, size_t, void*);
using DlIteratePhdrFunction = int (*)(DlIteratePhdrCallbackFunction, void*);
DlIteratePhdrFunction __dl_iterate_phdr;
[[gnu::weak]] DlIteratePhdrFunction __dl_iterate_phdr;
int dl_iterate_phdr(int (*callback)(struct dl_phdr_info* info, size_t size, void* data), void* data)
{

4
Userland/Libraries/LibC/ssp.cpp
View file

@ -18,8 +18,8 @@
extern "C" {
extern uintptr_t __stack_chk_guard;
// Initialized in `initialize_libc` (we leave a placeholder value here before initialization).
__attribute__((used)) uintptr_t __stack_chk_guard = (uintptr_t)0xc6c7c8c9;
// Populated by DynamicLinker in shared executables.
[[gnu::weak]] uintptr_t __stack_chk_guard = (uintptr_t)0xc6c7c8c9;
__attribute__((noreturn)) void __stack_chk_fail()
{

2
Userland/Libraries/LibC/stdlib.cpp
View file

@ -345,7 +345,7 @@ static T c_str_to_floating_point(char const* str, char** endptr)
extern "C" {
void (*__call_fini_functions)();
[[gnu::weak]] void (*__call_fini_functions)();
void exit(int status)
{