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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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19
Userland/Libraries/LibELF/DynamicObject.cpp
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@ -249,14 +249,8 @@ DynamicObject::RelocationSection DynamicObject::plt_relocation_section() const
return RelocationSection(Section(*this, m_plt_relocation_offset_location, m_size_of_plt_relocation_entry_list, m_size_of_relocation_entry, "DT_JMPREL"));
}
auto DynamicObject::HashSection::lookup_symbol(const StringView& name) const -> Optional<Symbol>
auto DynamicObject::HashSection::lookup_elf_symbol(const StringView& name, u32 hash_value) const -> Optional<Symbol>
{
return (this->*(m_lookup_function))(name);
}
auto DynamicObject::HashSection::lookup_elf_symbol(const StringView& name) const -> Optional<Symbol>
{
u32 hash_value = compute_sysv_hash(name);
u32* hash_table_begin = (u32*)address().as_ptr();
size_t num_buckets = hash_table_begin[0];
@ -279,7 +273,7 @@ auto DynamicObject::HashSection::lookup_elf_symbol(const StringView& name) const
return {};
}
auto DynamicObject::HashSection::lookup_gnu_symbol(const StringView& name) const -> Optional<Symbol>
auto DynamicObject::HashSection::lookup_gnu_symbol(const StringView& name, u32 hash_value) const -> Optional<Symbol>
{
// Algorithm reference: https://ent-voy.blogspot.com/2011/02/
// TODO: Handle 64bit bloomwords for ELF_CLASS64
@ -299,7 +293,7 @@ auto DynamicObject::HashSection::lookup_gnu_symbol(const StringView& name) const
const u32* const buckets = &bloom_words[num_maskwords];
const u32* const chains = &buckets[num_buckets];
BloomWord hash1 = compute_gnu_hash(name);
BloomWord hash1 = hash_value;
BloomWord hash2 = hash1 >> shift2;
const BloomWord bitmask = (1 << (hash1 % bloom_word_size)) | (1 << (hash2 % bloom_word_size));
@ -431,7 +425,12 @@ static const char* name_for_dtag(Elf32_Sword d_tag)
auto DynamicObject::lookup_symbol(const StringView& name) const -> Optional<SymbolLookupResult>
{
auto result = hash_section().lookup_symbol(name);
return lookup_symbol(name, compute_gnu_hash(name), compute_sysv_hash(name));
}
auto DynamicObject::lookup_symbol(const StringView& name, u32 gnu_hash, u32 sysv_hash) const -> Optional<SymbolLookupResult>
{
auto result = hash_section().lookup_symbol(name, gnu_hash, sysv_hash);
if (!result.has_value())
return {};
auto symbol = result.value();