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glld/mac] Don't add names of unreferenced symbols to string table 

Before this, a hello world program would contain many many unnecessary
entries in its string table.

No behavior change, just makes the string table in the output smaller
and more like ld64's.

Differential Revision: https://reviews.llvm.org/D93711
This commit is contained in:
Nico Weber 2020-12-22 11:00:57 -05:00
parent 7ec7788ac1
commit 57ffbe020a
2 changed files with 15 additions and 13 deletions
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22
lld/MachO/SyntheticSections.cpp
View File

@ -694,6 +694,11 @@ void SymtabSection::emitStabs() {
}
void SymtabSection::finalizeContents() {
auto addSymbol = [&](std::vector<SymtabEntry> &symbols, Symbol *sym) {
uint32_t strx = stringTableSection.addString(sym->getName());
symbols.push_back({sym, strx});
};
// Local symbols aren't in the SymbolTable, so we walk the list of object
// files to gather them.
for (InputFile *file : inputFiles) {
@ -702,10 +707,8 @@ void SymtabSection::finalizeContents() {
// TODO: when we implement -dead_strip, we should filter out symbols
// that belong to dead sections.
if (auto *defined = dyn_cast<Defined>(sym)) {
if (!defined->isExternal()) {
uint32_t strx = stringTableSection.addString(sym->getName());
localSymbols.push_back({sym, strx});
}
if (!defined->isExternal())
addSymbol(localSymbols, sym);
}
}
}
@ -713,19 +716,16 @@ void SymtabSection::finalizeContents() {
// __dyld_private is a local symbol too. It's linker-created and doesn't
// exist in any object file.
if (Defined* dyldPrivate = in.stubHelper->dyldPrivate) {
uint32_t strx = stringTableSection.addString(dyldPrivate->getName());
localSymbols.push_back({dyldPrivate, strx});
}
if (Defined* dyldPrivate = in.stubHelper->dyldPrivate)
addSymbol(localSymbols, dyldPrivate);
for (Symbol *sym : symtab->getSymbols()) {
uint32_t strx = stringTableSection.addString(sym->getName());
if (auto *defined = dyn_cast<Defined>(sym)) {
assert(defined->isExternal());
externalSymbols.push_back({sym, strx});
addSymbol(externalSymbols, sym);
} else if (auto *dysym = dyn_cast<DylibSymbol>(sym)) {
if (dysym->isReferenced())
undefinedSymbols.push_back({sym, strx});
addSymbol(undefinedSymbols, sym);
}
}

6
lld/test/MachO/symtab.s
View File

@ -86,17 +86,19 @@
# CHECK-NEXT: iundefsym: 5
# CHECK-NEXT: nundefsym: 2
## Verify that the first entry in the StringTable is a space.
## Verify that the first entry in the StringTable is a space, and that
## unreferenced symbols aren't emitted.
# RUN: obj2yaml %t/test | FileCheck %s --check-prefix=YAML
# YAML: StringTable:
# YAML-NEXT: ' '
# YAML-NOT: _unreferenced
#--- libfoo.s
.globl _dynamic
_dynamic:
#--- test.s
.globl _main, _external, _external_weak
.globl _main, _external, _external_weak, _unreferenced
.data
_external: