[ELF] --exclude-libs: localize defined libcall symbols referenced by lto.tmp

[MaskRay]

Summary

Fixes PR48681: after LTO, lto.tmp may reference a libcall symbol not in an IR
symbol table of any bitcode file. If such a symbol is defined in an archive
matched by a --exclude-libs, we don't correctly localize the symbol.

Add another excludeLibs after compileBitcodeFiles to localize such libcall
symbols. Unfortunately we have keep the existing one for D43126.

As I understand it, using VER_NDX_LOCAL is an implementation detail of
--exclude-libs and the symbol ... has undefined version ... error should not
be exempted. Ideally we should error as GNU ld does.

[MaskRay]

Add REQUIRES

[MaskRay]

lld/test/ELF/lto/exclude-libs-libcall.ll

3

Forgot to add a comment:

lto.tmp may reference a libcall symbol not in the IR symbol table. If such a symbol is defined in an archive matched by a --exclude-libs, the symbol should be localized.

[psmith]

LGTM, may be worth waiting for any other comments.

I reported the Bionic issue mentioned in D43126 under https://issuetracker.google.com/issues/73020933 . From memory it was possible to work around the failure by providing a symbol versioning script but I wasn't able to convince the maintainer it was worthwhile. May be worth having another try?

lld/ELF/Driver.cpp

template <class ELFT> void LinkerDriver::link(opt::InputArgList &args) {
   if (errorCount())
     return;
 
   // We want to declare linker script's symbols early,
   // so that we can version them.
   // They also might be exported if referenced by DSOs.
   script->declareSymbols();
 
-  // Handle the -exclude-libs option.
+  // Handle --exclude-libs. This is before scanVersionScript() due to a
+  // workaround for Android ndk: for a defined versioned symbol in an archive
+  // without a version node in the version script, Android does not expect a
+  // 'has undefined version' error in -shared --exclude-libs=ALL mode (PR36295).
+  // GNU ld errors in this case.
   if (args.hasArg(OPT_exclude_libs))
     excludeLibs(args);
 
   // Create elfHeader early. We need a dummy section in
   // addReservedSymbols to mark the created symbols as not absolute.
   Out::elfHeader = make<OutputSection>("", 0, SHF_ALLOC);
   Out::elfHeader->size = sizeof(typename ELFT::Ehdr);
 
template <class ELFT> void LinkerDriver::link(opt::InputArgList &args) {
 
   // Do link-time optimization if given files are LLVM bitcode files.
   // This compiles bitcode files into real object files.
   //
   // With this the symbol table should be complete. After this, no new names
   // except a few linker-synthesized ones will be added to the symbol table.
   compileBitcodeFiles<ELFT>();
 
+  // Handle --exclude-libs again because lto.tmp may reference additional
+  // libcalls symbols defined in an excluded archive.
+  if (args.hasArg(OPT_exclude_libs))
+    excludeLibs(args);
+
   // Symbol resolution finished. Report backward reference problems.
   reportBackrefs();
   if (errorCount())
     return;
 
   // If -thinlto-index-only is given, we should create only "index
   // files" and not object files. Index file creation is already done
   // in addCombinedLTOObject, so we are done if that's the case.

lld/test/ELF/lto/exclude-libs-libcall.ll

+; RUN: rm -rf %t && split-file %s %t
+; RUN: llvm-as %t/a.ll -o %t/a.bc
+; RUN: llvm-mc -filetype=obj -triple=x86_64 %t/b.s -o %t/b.o
+; RUN: llvm-ar rc %t/b.a %t/b.o
+; RUN: ld.lld -shared --exclude-libs=b.a %t/a.bc %t/b.a -o %t.so -y __divti3 2>&1 | FileCheck %s --check-prefix=TRACE
+; RUN: llvm-readelf --dyn-syms %t.so | FileCheck %s
+
+; TRACE:      {{.*}}/b.a: lazy definition of __divti3
+; TRACE-NEXT: lto.tmp: reference to __divti3
+; TRACE-NEXT: {{.*}}/b.a(b.o): definition of __divti3
+
+; CHECK:     Symbol table '.dynsym' contains 2 entries:
+; CHECK-NOT: __divti3
+
+;--- a.ll
+target triple = "x86_64-unknown-linux"
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+
+define i128 @foo(i128 %x, i128 %y) {
+entry:
+  %div = sdiv i128 %x, %y
+  ret i128 %div
+}
+
+;--- b.s
+.globl __divti3
+__divti3: