[lld] d098651 - [LLD] [COFF] Preserve directives and export names from LTO objects (#78802)

[via llvm-commits]

Author: Martin Storsjö
Date: 2024-01-20T16:15:44+02:00
New Revision: d0986519d58e6d71656019cfa6604efa4bf6d3e7

URL: https://github.com/llvm/llvm-project/commit/d0986519d58e6d71656019cfa6604efa4bf6d3e7
DIFF: https://github.com/llvm/llvm-project/commit/d0986519d58e6d71656019cfa6604efa4bf6d3e7.diff

LOG: [LLD] [COFF] Preserve directives and export names from LTO objects (#78802)

The export names are saved as StringRefs pointing into the COFF
directives. In the case of LTO objects, this can be memory allocated
that is owned by the LTO InputFile, which gets destructed when doing the
compilation.

In the case of LTO objects from an older version of LLVM, which require
being upgraded when loaded, the directives string gets destructed, while
when using LTO objects of a matching version (the common case), the
directives string points into memory that doesn't get destructed on LTO
compilation.

Test this by linking a bundled binary LTO object file, from an older
version of LLVM.

This fixes issue #78591, and downstream issue
https://github.com/mstorsjo/llvm-mingw/issues/392.

Added: 
    lld/test/COFF/Inputs/lto-directives.obj
    lld/test/COFF/lto-directives.test

Modified: 
    lld/COFF/InputFiles.cpp

Removed: 
    


################################################################################
diff  --git a/lld/COFF/InputFiles.cpp b/lld/COFF/InputFiles.cpp
index cd744800cb0dec..22cc0e3e5dbaf7 100644
--- a/lld/COFF/InputFiles.cpp
+++ b/lld/COFF/InputFiles.cpp
@@ -1081,7 +1081,7 @@ void BitcodeFile::parse() {
     if (objSym.isUsed())
       ctx.config.gcroot.push_back(sym);
   }
-  directives = obj->getCOFFLinkerOpts();
+  directives = saver.save(obj->getCOFFLinkerOpts());
 }
 
 void BitcodeFile::parseLazy() {

diff  --git a/lld/test/COFF/Inputs/lto-directives.obj b/lld/test/COFF/Inputs/lto-directives.obj
new file mode 100644
index 00000000000000..a413b0ab92f4e4
Binary files /dev/null and b/lld/test/COFF/Inputs/lto-directives.obj 
diff er

diff  --git a/lld/test/COFF/lto-directives.test b/lld/test/COFF/lto-directives.test
new file mode 100644
index 00000000000000..5890d426764c4e
--- /dev/null
+++ b/lld/test/COFF/lto-directives.test
@@ -0,0 +1,15 @@
+; REQUIRES: x86
+
+;; Test linking an LTO object file that contains directives. The
+;; LTO object file is built with an older toolchain, to force it
+;; to be upgraded when loaded.
+
+;; The input file is compiled from source that looks like this:
+;;   void __declspec(dllexport) entry(void) { }
+;; with this command:
+;;   clang -target x86_64-windows-msvc -c main.c -flto
+
+; RUN: lld-link /entry:entry /subsystem:console %p/Inputs/lto-directives.obj /dll /out:%t.dll
+; RUN: llvm-readobj --coff-exports %t.dll | FileCheck %s
+
+; CHECK: Name: entry