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LibELF: Support relocating weak symbols against global libraries

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A strong symbol anywhere in an executable must override any
weak symbol used in any library. This means that the weak symbol
must be overridden by a strong symbol even if the strong symbol
is in a dependent library. This means we need to perform relocations
twice, and resolve weak symbols globally before attempting to resolve
them locally. Consequentially we need to defer performing any
initialisations until after we have performed the second round of
relocations.
This commit is contained in:
William Marlow 2021-01-02 00:48:19 +00:00 • committed by Andreas Kling
parent 3e815ad5b1
commit 05345fc07d
4 changed files with 189 additions and 148 deletions
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20
Libraries/LibELF/DynamicLoader.h
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@ -52,11 +52,11 @@ public:
// from the SHT_DYNAMIC in the file.
RefPtr<DynamicObject> load_from_image(unsigned flags, size_t total_tls_size);
// Stage 2 of loading: relocations and init functions
// Assumes that the program headers have been loaded and that m_dynamic_object is initialized
// Splitting loading like this allows us to use the same code to relocate a main executable as an elf binary
// Stage 2 of loading: dynamic object loading and primary relocations
bool load_stage_2(unsigned flags, size_t total_tls_size);
// Stage 3 of loading: lazy relocations and initializers
RefPtr<DynamicObject> load_stage_3(unsigned flags, size_t total_tls_size);
// Intended for use by dlsym or other internal methods
void* symbol_for_name(const char*);
@ -114,11 +114,21 @@ private:
void load_program_headers();
// Stage 2
void do_relocations(size_t total_tls_size);
void do_main_relocations(size_t total_tls_size);
// Stage 3
void do_lazy_relocations(size_t total_tls_size);
void setup_plt_trampoline();
void call_object_init_functions();
bool validate();
enum class RelocationResult : uint8_t {
Failed = 0,
Success = 1,
ResolveLater = 2,
};
RelocationResult do_relocation(size_t total_tls_size, DynamicObject::Relocation relocation);
size_t calculate_tls_size() const;
DynamicObject::SymbolLookupResult lookup_symbol(const ELF::DynamicObject::Symbol& symbol) const;
@ -141,6 +151,8 @@ private:
size_t m_tls_offset { 0 };
size_t m_tls_size { 0 };
Vector<DynamicObject::Relocation> m_unresolved_relocations;
};
template<typename F>