[llvm] 82d0749 - [TargetLoweringObjectFileImpl] Make .llvmbc and .llvmcmd non-SHF_ALLOC

[Fangrui Song via llvm-commits]

Author: Fangrui Song
Date: 2020-08-25T13:37:29-07:00
New Revision: 82d0749749fafb0303414131dc570781376fdcfb

URL: https://github.com/llvm/llvm-project/commit/82d0749749fafb0303414131dc570781376fdcfb
DIFF: https://github.com/llvm/llvm-project/commit/82d0749749fafb0303414131dc570781376fdcfb.diff

LOG: [TargetLoweringObjectFileImpl] Make .llvmbc and .llvmcmd non-SHF_ALLOC

There are two ways .llvmbc can be produced:

* clang -c -fembed-bitcode=all (which also produces .llvmcmd)
* LTO backend: ld.lld -mllvm -lto-embed-bitcode or -plugin-opt=-lto-embed-bitcode

.llvmbc and .llvmcmd have the SHF_ALLOC flag, so they can be dropped by
--gc-sections.

This patch sets SectionKind::Metadata to drop the SHF_ALLOC flag. This
is conceptually correct: the two sections are not part of the process
image, so SHF_ALLOC is not appropriate.

`test/LTO/X86/embed-bitcode.ll`: changed `llvm-objcopy -O binary --only-section` to
`llvm-objcopy --dump-section`. `-O binary` does not dump non-SHF_ALLOC sections.

Reviewed By: tejohnson

Differential Revision: https://reviews.llvm.org/D86374

Added: 
    llvm/test/CodeGen/X86/embed-bitcode.ll

Modified: 
    llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
    llvm/test/LTO/X86/embed-bitcode.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
index 4c3e6cce7836..c2ea5d9b860a 100644
--- a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
@@ -436,7 +436,8 @@ static SectionKind getELFKindForNamedSection(StringRef Name, SectionKind K) {
   if (Name == getInstrProfSectionName(IPSK_covmap, Triple::ELF,
                                       /*AddSegmentInfo=*/false) ||
       Name == getInstrProfSectionName(IPSK_covfun, Triple::ELF,
-                                      /*AddSegmentInfo=*/false))
+                                      /*AddSegmentInfo=*/false) ||
+      Name == ".llvmbc" || Name == ".llvmcmd")
     return SectionKind::getMetadata();
 
   if (Name.empty() || Name[0] != '.') return K;

diff  --git a/llvm/test/CodeGen/X86/embed-bitcode.ll b/llvm/test/CodeGen/X86/embed-bitcode.ll
new file mode 100644
index 000000000000..00dd7ef17d56
--- /dev/null
+++ b/llvm/test/CodeGen/X86/embed-bitcode.ll
@@ -0,0 +1,10 @@
+; RUN: llc -filetype=obj -mtriple=x86_64 %s -o %t
+; RUN: llvm-readelf -S %t | FileCheck %s
+
+; CHECK:      .text    PROGBITS 0000000000000000 [[#%x,OFF:]] 000000 00 AX 0
+; CHECK-NEXT: .llvmbc  PROGBITS 0000000000000000 [[#%x,OFF:]] 000004 00    0
+; CHECK-NEXT: .llvmcmd PROGBITS 0000000000000000 [[#%x,OFF:]] 000005 00    0
+
+ at llvm.embedded.module = private constant [4 x i8] c"BC\C0\DE", section ".llvmbc"
+ at llvm.cmdline = private constant [5 x i8] c"-cc1\00", section ".llvmcmd"
+ at llvm.compiler.used = appending global [2 x i8*] [i8* getelementptr inbounds ([4 x i8], [4 x i8]* @llvm.embedded.module, i32 0, i32 0), i8* getelementptr inbounds ([5 x i8], [5 x i8]* @llvm.cmdline, i32 0, i32 0)], section "llvm.metadata"

diff  --git a/llvm/test/LTO/X86/embed-bitcode.ll b/llvm/test/LTO/X86/embed-bitcode.ll
index f57ea1fa32ae..151f27f55eef 100644
--- a/llvm/test/LTO/X86/embed-bitcode.ll
+++ b/llvm/test/LTO/X86/embed-bitcode.ll
@@ -10,11 +10,11 @@
 
 ; RUN: llvm-lto2 run -r %t1.o,_start,px -r %t2.o,foo,px -r %t3.o,bar,px -r %t2.o,bar,lx -lto-embed-bitcode -o %t3 %t1.o %t2.o %t3.o
 ; RUN: llvm-readelf -S %t3.0 | FileCheck %s --check-prefix=CHECK-ELF
-; RUN: llvm-objcopy -O binary -j .llvmbc %t3.0 %t-embedded.bc
+; RUN: llvm-objcopy --dump-section=.llvmbc=%t-embedded.bc %t3.0 /dev/null
 ; RUN: llvm-dis %t-embedded.bc -o - | FileCheck %s --check-prefix=CHECK-LL
 
-; CHECK-ELF: .text
-; CHECK-ELF: .llvmbc
+; CHECK-ELF:      .text   PROGBITS 0000000000000000 [[#%x,OFF:]] [[#%x,SIZE:]] 00 AX 0
+; CHECK-ELF-NEXT: .llvmbc PROGBITS 0000000000000000 [[#%x,OFF:]] [[#%x,SIZE:]] 00    0
 
 ; CHECK-LL: @_start
 ; CHECK-LL: @foo