[llvm] 4b1e3d1 - [gold] Ignore bitcode from sections inside object files
Tom Stellard via llvm-commits
llvm-commits at lists.llvm.org
Thu Jul 14 14:46:44 PDT 2022
Author: Tom Stellard
Date: 2022-07-14T14:46:15-07:00
New Revision: 4b1e3d19370694dd2b2c04a5945f3f9e43917456
URL: https://github.com/llvm/llvm-project/commit/4b1e3d19370694dd2b2c04a5945f3f9e43917456
DIFF: https://github.com/llvm/llvm-project/commit/4b1e3d19370694dd2b2c04a5945f3f9e43917456.diff
LOG: [gold] Ignore bitcode from sections inside object files
-fembed-bitcode will put bitcode into special sections within object
files, but this is not meant to be used by LTO, so the gold plugin
should ignore it.
https://github.com/llvm/llvm-project/issues/47216
Reviewed By: tejohnson, MaskRay
Differential Revision: https://reviews.llvm.org/D116995
Added:
llvm/test/tools/gold/X86/Inputs/bcsection-lib.ll
Modified:
llvm/docs/BitCodeFormat.rst
llvm/docs/GoldPlugin.rst
llvm/docs/ReleaseNotes.rst
llvm/test/tools/gold/X86/Inputs/bcsection.s
llvm/test/tools/gold/X86/bcsection.ll
llvm/tools/gold/gold-plugin.cpp
Removed:
################################################################################
diff --git a/llvm/docs/BitCodeFormat.rst b/llvm/docs/BitCodeFormat.rst
index 56268f1523cc4..d581e18d6daaa 100644
--- a/llvm/docs/BitCodeFormat.rst
+++ b/llvm/docs/BitCodeFormat.rst
@@ -475,7 +475,8 @@ formats. This wrapper format is useful for accommodating LTO in compilation
pipelines where intermediate objects must be native object files which contain
metadata in other sections.
-Not all tools support this format.
+Not all tools support this format. For example, lld and the gold plugin will
+ignore these sections when linking object files.
.. _encoding of LLVM IR:
diff --git a/llvm/docs/GoldPlugin.rst b/llvm/docs/GoldPlugin.rst
index ce310bc2cf3c0..07d2fc203eba5 100644
--- a/llvm/docs/GoldPlugin.rst
+++ b/llvm/docs/GoldPlugin.rst
@@ -17,6 +17,10 @@ and above also supports LTO via plugins. However, usage of the LLVM
gold plugin with ld.bfd is not tested and therefore not officially
supported or recommended.
+As of LLVM 15, the gold plugin will ignore bitcode from the ``.llvmbc``
+section inside of ELF object files. However, LTO with bitcode files
+is still supported.
+
.. _`gold linker`: http://sourceware.org/binutils
.. _`GCC LTO`: http://gcc.gnu.org/wiki/LinkTimeOptimization
.. _`gold plugin interface`: http://gcc.gnu.org/wiki/whopr/driver
diff --git a/llvm/docs/ReleaseNotes.rst b/llvm/docs/ReleaseNotes.rst
index f9fc516aa433a..3f83671c6c6b0 100644
--- a/llvm/docs/ReleaseNotes.rst
+++ b/llvm/docs/ReleaseNotes.rst
@@ -251,6 +251,9 @@ Changes to the LLVM tools
* :doc:`llvm-objcopy <CommandGuide/llvm-objcopy>` has removed support for the legacy ``zlib-gnu`` format.
* :doc:`llvm-objcopy <CommandGuide/llvm-objcopy>` now allows ``--set-section-flags src=... --rename-section src=tst``.
``--add-section=.foo1=... --rename-section=.foo1=.foo2`` now adds ``.foo1`` instead of ``.foo2``.
+* The LLVM gold plugin now ignores bitcode from the ``.llvmbc`` section of ELF
+ files when doing LTO. https://github.com/llvm/llvm-project/issues/47216
+>>>>>>> bbd6f1cd6d16... [gold] Ignore bitcode from sections inside object files
Changes to LLDB
---------------------------------
diff --git a/llvm/test/tools/gold/X86/Inputs/bcsection-lib.ll b/llvm/test/tools/gold/X86/Inputs/bcsection-lib.ll
new file mode 100644
index 0000000000000..ef3557c19cdc6
--- /dev/null
+++ b/llvm/test/tools/gold/X86/Inputs/bcsection-lib.ll
@@ -0,0 +1,6 @@
+declare void @elf_func()
+
+define i32 @lib_func() {
+ call void @elf_func()
+ ret i32 0
+}
diff --git a/llvm/test/tools/gold/X86/Inputs/bcsection.s b/llvm/test/tools/gold/X86/Inputs/bcsection.s
index ede1e5c532dd1..c523612563b44 100644
--- a/llvm/test/tools/gold/X86/Inputs/bcsection.s
+++ b/llvm/test/tools/gold/X86/Inputs/bcsection.s
@@ -1,2 +1,7 @@
+.global elf_func
+
+elf_func:
+ ret
+
.section .llvmbc
.incbin "bcsection.bc"
diff --git a/llvm/test/tools/gold/X86/bcsection.ll b/llvm/test/tools/gold/X86/bcsection.ll
index 6d3481f8f9665..09882d83fe917 100644
--- a/llvm/test/tools/gold/X86/bcsection.ll
+++ b/llvm/test/tools/gold/X86/bcsection.ll
@@ -2,16 +2,29 @@
; RUN: llvm-as -o %t/bcsection.bc %s
; RUN: llvm-mc -I=%t -filetype=obj -triple=x86_64-unknown-unknown -o %t/bcsection.bco %p/Inputs/bcsection.s
-; RUN: llvm-nm --no-llvm-bc %t/bcsection.bco 2>&1 | FileCheck %s -check-prefix=NO-SYMBOLS
-; NO-SYMBOLS: no symbols
+; RUN: llc -filetype=obj -mtriple=x86_64-unknown-unknown -o %t/bcsection-lib.o %p/Inputs/bcsection-lib.ll
-; RUN: %gold -r -o %t/bcsection.o -m elf_x86_64 -plugin %llvmshlibdir/LLVMgold%shlibext %t/bcsection.bco
-; RUN: llvm-nm --no-llvm-bc %t/bcsection.o | FileCheck %s
+; RUN: %gold -shared --no-undefined -o %t/bcsection.so -m elf_x86_64 -plugin %llvmshlibdir/LLVMgold%shlibext %t/bcsection.bco %t/bcsection-lib.o
+
+; This test checks that the gold plugin does not attempt to use the bitcode
+; in the .llvmbc section for LTO. bcsection-lib.o calls a function that is
+; present the symbol table of bcsection.bco, but not included in the embedded
+; bitcode. If the linker were to use the bitcode, then the symbols in the
+; symbol table of bcsection.bco will be ignored and the link will fail.
+;
+; bcsection.bco:
+; .text:
+; elf_func
+; .llvmbc:
+; bitcode_func
+;
+; bcsection-lib.o:
+; calls elf_func()
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-unknown"
; CHECK: main
-define i32 @main() {
+define i32 @bitcode_func() {
ret i32 0
}
diff --git a/llvm/tools/gold/gold-plugin.cpp b/llvm/tools/gold/gold-plugin.cpp
index 9a0264d0c1dd1..f1b457bb4f5ba 100644
--- a/llvm/tools/gold/gold-plugin.cpp
+++ b/llvm/tools/gold/gold-plugin.cpp
@@ -542,6 +542,14 @@ static ld_plugin_status claim_file_hook(const ld_plugin_input_file *file,
BufferRef = Buffer->getMemBufferRef();
}
+ // Only use bitcode files for LTO. InputFile::create() will load bitcode
+ // from the .llvmbc section within a binary object, this bitcode is typically
+ // generated by -fembed-bitcode and is not to be used by LLVMgold.so for LTO.
+ if (identify_magic(BufferRef.getBuffer()) != file_magic::bitcode) {
+ *claimed = 0;
+ return LDPS_OK;
+ }
+
*claimed = 1;
Expected<std::unique_ptr<InputFile>> ObjOrErr = InputFile::create(BufferRef);
More information about the llvm-commits
mailing list