[lld] ac2224c - [ELF] --exclude-libs: localize defined libcall symbols referenced by lto.tmp

[Fangrui Song via llvm-commits]

Author: Fangrui Song
Date: 2021-01-11T09:33:22-08:00
New Revision: ac2224c02282039f41294842396cbbe47ea29a23

URL: https://github.com/llvm/llvm-project/commit/ac2224c02282039f41294842396cbbe47ea29a23
DIFF: https://github.com/llvm/llvm-project/commit/ac2224c02282039f41294842396cbbe47ea29a23.diff

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

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.

Using VER_NDX_LOCAL is an implementation detail of `--exclude-libs`, it does not
necessarily tie to the "localize" behavior.  `local:` patterns in a version
script can be omitted.
The `symbol ... has undefined version ...` error should not be exempted.
Ideally we should error as GNU ld does. https://issuetracker.google.com/issues/73020933

Reviewed By: psmith

Differential Revision: https://reviews.llvm.org/D94280

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

Modified: 
    lld/ELF/Driver.cpp

Removed: 
    


################################################################################
diff  --git a/lld/ELF/Driver.cpp b/lld/ELF/Driver.cpp
index 5cc32f81c2ec..e1395a568ea2 100644
--- a/lld/ELF/Driver.cpp
+++ b/lld/ELF/Driver.cpp
@@ -2146,7 +2146,11 @@ template <class ELFT> void LinkerDriver::link(opt::InputArgList &args) {
   // 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);
 
@@ -2179,6 +2183,11 @@ template <class ELFT> void LinkerDriver::link(opt::InputArgList &args) {
   // 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())

diff  --git a/lld/test/ELF/lto/exclude-libs-libcall.ll b/lld/test/ELF/lto/exclude-libs-libcall.ll
new file mode 100644
index 000000000000..ece587f1c4da
--- /dev/null
+++ b/lld/test/ELF/lto/exclude-libs-libcall.ll
@@ -0,0 +1,28 @@
+; REQUIRES: x86
+; 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: