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LibELF: Make symbol lookup functions return Optional<Symbol>

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It was very confusing how these functions used the "undefined" state
of Symbol to signal lookup failure. Let's use Optional<T> to make things
a bit more understandable.
This commit is contained in:
Andreas Kling 2021-02-20 23:12:00 +01:00
parent 46c3ff2acf
commit 1997d5de1a
3 changed files with 24 additions and 24 deletions
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7
Userland/Libraries/LibELF/DynamicLoader.cpp
View file

@ -140,11 +140,12 @@ bool DynamicLoader::validate()
void* DynamicLoader::symbol_for_name(const StringView& name) void* DynamicLoader::symbol_for_name(const StringView& name)
{ {
auto symbol = m_dynamic_object->hash_section().lookup_symbol(name); auto result = m_dynamic_object->hash_section().lookup_symbol(name);
if (!result.has_value())
return nullptr;
auto symbol = result.value();
if (symbol.is_undefined()) if (symbol.is_undefined())
return nullptr; return nullptr;
return m_dynamic_object->base_address().offset(symbol.value()).as_ptr(); return m_dynamic_object->base_address().offset(symbol.value()).as_ptr();
} }

33
Userland/Libraries/LibELF/DynamicObject.cpp
View file

@ -278,17 +278,15 @@ u32 DynamicObject::HashSection::calculate_gnu_hash(const StringView& name)
return hash; return hash;
} }
auto DynamicObject::HashSection::lookup_symbol(const StringView& name) const -> Symbol auto DynamicObject::HashSection::lookup_symbol(const StringView& name) const -> Optional<Symbol>
{ {
return (this->*(m_lookup_function))(name); return (this->*(m_lookup_function))(name);
} }
DynamicObject::Symbol DynamicObject::HashSection::lookup_elf_symbol(const StringView& name) const auto DynamicObject::HashSection::lookup_elf_symbol(const StringView& name) const -> Optional<Symbol>
{ {
u32 hash_value = calculate_elf_hash(name); u32 hash_value = calculate_elf_hash(name);
u32* hash_table_begin = (u32*)address().as_ptr(); u32* hash_table_begin = (u32*)address().as_ptr();
size_t num_buckets = hash_table_begin[0]; size_t num_buckets = hash_table_begin[0];
// This is here for completeness, but, since we're using the fact that every chain // This is here for completeness, but, since we're using the fact that every chain
@ -307,10 +305,10 @@ DynamicObject::Symbol DynamicObject::HashSection::lookup_elf_symbol(const String
return symbol; return symbol;
} }
} }
return Symbol::create_undefined(m_dynamic); return {};
} }
DynamicObject::Symbol DynamicObject::HashSection::lookup_gnu_symbol(const StringView& name) const auto DynamicObject::HashSection::lookup_gnu_symbol(const StringView& name) const -> Optional<Symbol>
{ {
// Algorithm reference: https://ent-voy.blogspot.com/2011/02/ // Algorithm reference: https://ent-voy.blogspot.com/2011/02/
// TODO: Handle 64bit bloomwords for ELF_CLASS64 // TODO: Handle 64bit bloomwords for ELF_CLASS64
@ -334,19 +332,17 @@ DynamicObject::Symbol DynamicObject::HashSection::lookup_gnu_symbol(const String
BloomWord hash2 = hash1 >> shift2; BloomWord hash2 = hash1 >> shift2;
const BloomWord bitmask = (1 << (hash1 % bloom_word_size)) | (1 << (hash2 % bloom_word_size)); const BloomWord bitmask = (1 << (hash1 % bloom_word_size)) | (1 << (hash2 % bloom_word_size));
if ((bloom_words[(hash1 / bloom_word_size) & num_maskwords_bitmask] & bitmask) != bitmask) { if ((bloom_words[(hash1 / bloom_word_size) & num_maskwords_bitmask] & bitmask) != bitmask)
return Symbol::create_undefined(m_dynamic); return {};
}
size_t current_sym = buckets[hash1 % num_buckets]; size_t current_sym = buckets[hash1 % num_buckets];
if (current_sym == 0) { if (current_sym == 0)
return Symbol::create_undefined(m_dynamic); return {};
}
const u32* current_chain = &chains[current_sym - num_omitted_symbols]; const u32* current_chain = &chains[current_sym - num_omitted_symbols];
for (hash1 &= ~1;; ++current_sym) { for (hash1 &= ~1;; ++current_sym) {
hash2 = *(current_chain++); hash2 = *(current_chain++);
const auto symbol = m_dynamic.symbol(current_sym); auto symbol = m_dynamic.symbol(current_sym);
if ((hash1 == (hash2 & ~1)) && name == symbol.name()) { if ((hash1 == (hash2 & ~1)) && name == symbol.name()) {
dbgln_if(DYNAMIC_LOAD_DEBUG, "Returning GNU dynamic symbol with index {} for {}: {}", current_sym, symbol.name(), symbol.address().as_ptr()); dbgln_if(DYNAMIC_LOAD_DEBUG, "Returning GNU dynamic symbol with index {} for {}: {}", current_sym, symbol.name(), symbol.address().as_ptr());
return symbol; return symbol;
@ -356,7 +352,7 @@ DynamicObject::Symbol DynamicObject::HashSection::lookup_gnu_symbol(const String
} }
} }
return Symbol::create_undefined(m_dynamic); return {};
} }
StringView DynamicObject::symbol_string_table_string(Elf32_Word index) const StringView DynamicObject::symbol_string_table_string(Elf32_Word index) const
@ -464,10 +460,13 @@ static const char* name_for_dtag(Elf32_Sword d_tag)
Optional<DynamicObject::SymbolLookupResult> DynamicObject::lookup_symbol(const StringView& name) const Optional<DynamicObject::SymbolLookupResult> DynamicObject::lookup_symbol(const StringView& name) const
{ {
auto res = hash_section().lookup_symbol(name); auto result = hash_section().lookup_symbol(name);
if (res.is_undefined()) if (!result.has_value())
return {}; return {};
return SymbolLookupResult { res.value(), (FlatPtr)res.address().as_ptr(), res.bind(), this }; auto symbol = result.value();
if (symbol.is_undefined())
return {};
return SymbolLookupResult { symbol.value(), symbol.address().get(), symbol.bind(), this };
} }
NonnullRefPtr<DynamicObject> DynamicObject::create(VirtualAddress base_address, VirtualAddress dynamic_section_address) NonnullRefPtr<DynamicObject> DynamicObject::create(VirtualAddress base_address, VirtualAddress dynamic_section_address)

8
Userland/Libraries/LibELF/DynamicObject.h
View file

@ -219,16 +219,16 @@ public:
} }
} }
Symbol lookup_symbol(const StringView& name) const; Optional<Symbol> lookup_symbol(const StringView& name) const;
private: private:
static u32 calculate_elf_hash(const StringView& name); static u32 calculate_elf_hash(const StringView& name);
static u32 calculate_gnu_hash(const StringView& name); static u32 calculate_gnu_hash(const StringView& name);
DynamicObject::Symbol lookup_elf_symbol(const StringView& name) const; Optional<Symbol> lookup_elf_symbol(const StringView& name) const;
DynamicObject::Symbol lookup_gnu_symbol(const StringView& name) const; Optional<Symbol> lookup_gnu_symbol(const StringView& name) const;
typedef DynamicObject::Symbol (HashSection::*LookupFunction)(const StringView&) const; typedef Optional<Symbol> (HashSection::*LookupFunction)(const StringView&) const;
LookupFunction m_lookup_function {}; LookupFunction m_lookup_function {};
}; };