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[ELF] - Resolve references properly when using .symver directive 

This is PR28414. 
Previously LLD was unable to link following:
(failed with undefined symbol bar)

```
Version script:
SOME_VERSION { global: *; };

.global _start
.global bar
.symver _start, bar@@SOME_VERSION
_start:
  jmp bar
```

Manual has next description:
//
.symver name, name2@@nodename
In this case, the symbol name must exist and be defined within the file being assembled. It is similar to name2@nodename. 
**The difference is name2@@nodename will also be used to resolve references to name2 by the linker**
https://sourceware.org/binutils/docs/as/Symver.html
//

Patch implements that. If we have name@@ver symbol and name is undefined, 
name@@ver is used to resolve references to name.

Differential revision: https://reviews.llvm.org/D33680

llvm-svn: 306813
This commit is contained in:
George Rimar 2017-06-30 10:19:54 +00:00
parent d8508b0af3
commit aad84e2ee2
2 changed files with 31 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

24
lld/ELF/SymbolTable.cpp
View File

@ -712,15 +712,31 @@ void SymbolTable<ELFT>::assignWildcardVersion(SymbolVersion Ver,
B->symbol()->VersionId = VersionId;
}
static bool isDefaultVersion(SymbolBody *B) {
return B->isInCurrentDSO() && B->getName().find("@@") != StringRef::npos;
}
// This function processes version scripts by updating VersionId
// member of symbols.
template <class ELFT> void SymbolTable<ELFT>::scanVersionScript() {
// Symbol themselves might know their versions because symbols
// can contain versions in the form of <name>@<version>.
// Let them parse their names.
if (!Config->VersionDefinitions.empty())
for (Symbol *Sym : SymVector)
Sym->body()->parseSymbolVersion();
// Let them parse and update their names to exclude version suffix.
for (Symbol *Sym : SymVector) {
SymbolBody *Body = Sym->body();
bool IsDefault = isDefaultVersion(Body);
Body->parseSymbolVersion();
if (!IsDefault)
continue;
// <name>@@<version> means the symbol is the default version. If that's the
// case, the symbol is not used only to resolve <name> of version <version>
// but also undefined unversioned symbols with name <name>.
SymbolBody *S = find(Body->getName());
if (S && S->isUndefined())
S->copy(Body);
}
// Handle edge cases first.
handleAnonymousVersion();

11
lld/test/ELF/version-script-symver.s Normal file
View File

@ -0,0 +1,11 @@
# REQUIRES: x86
# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
# RUN: echo "VERSION { global: *; };" > %t.map
# RUN: ld.lld %t.o --version-script %t.map -o %t
.global _start
.global bar
.symver _start, bar@@VERSION
_start:
jmp bar