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

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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
This commit is contained in:
Fangrui Song 2020-08-25 13:37:29 -07:00 committed by Fangrui Song
parent d984833f21
commit 0c234a7fc0
3 changed files with 15 additions and 4 deletions
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3
lib/CodeGen/TargetLoweringObjectFileImpl.cpp
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@ -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;

10
test/CodeGen/X86/embed-bitcode.ll Normal file
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@ -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
@llvm.embedded.module = private constant [4 x i8] c"BC\C0\DE", section ".llvmbc"
@llvm.cmdline = private constant [5 x i8] c"-cc1\00", section ".llvmcmd"
@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"

6
test/LTO/X86/embed-bitcode.ll
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@ -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