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LibELF: Don't recompute the same ELF hashes over and over

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When performing a global symbol lookup, we were recomputing the symbol
hashes once for every dynamic object searched. The hash function was
at the very top of a profile (15%) of program startup.

With this change, the hash function is no longer visible among the top
stacks in the profile. :^)
This commit is contained in:
Andreas Kling 2021-02-23 18:44:09 +01:00
parent af6a633468
commit d6af3302e8
4 changed files with 29 additions and 27 deletions
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27
Userland/Libraries/LibELF/DynamicObject.h
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@ -184,27 +184,22 @@ public:
public:
HashSection(const Section& section, HashType hash_type)
: Section(section.m_dynamic, section.m_section_offset, section.m_section_size_bytes, section.m_entry_size, section.m_name)
, m_hash_type(hash_type)
{
switch (hash_type) {
case HashType::SYSV:
m_lookup_function = &HashSection::lookup_elf_symbol;
break;
case HashType::GNU:
m_lookup_function = &HashSection::lookup_gnu_symbol;
break;
default:
ASSERT_NOT_REACHED();
}
}
Optional<Symbol> lookup_symbol(const StringView& name) const;
Optional<Symbol> lookup_symbol(const StringView& name, u32 gnu_hash, u32 sysv_hash) const
{
if (m_hash_type == HashType::SYSV)
return lookup_elf_symbol(name, sysv_hash);
return lookup_gnu_symbol(name, gnu_hash);
}
private:
Optional<Symbol> lookup_elf_symbol(const StringView& name) const;
Optional<Symbol> lookup_gnu_symbol(const StringView& name) const;
Optional<Symbol> lookup_elf_symbol(const StringView& name, u32 hash) const;
Optional<Symbol> lookup_gnu_symbol(const StringView& name, u32 hash) const;
typedef Optional<Symbol> (HashSection::*LookupFunction)(const StringView&) const;
LookupFunction m_lookup_function {};
HashType m_hash_type {};
};
unsigned symbol_count() const { return m_symbol_count; }
@ -256,7 +251,9 @@ public:
unsigned bind { STB_LOCAL };
const ELF::DynamicObject* dynamic_object { nullptr }; // The object in which the symbol is defined
};
Optional<SymbolLookupResult> lookup_symbol(const StringView& name) const;
Optional<SymbolLookupResult> lookup_symbol(const StringView& name, u32 gnu_hash, u32 sysv_hash) const;
// Will be called from _fixup_plt_entry, as part of the PLT trampoline
VirtualAddress patch_plt_entry(u32 relocation_offset);