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llvm-project/lld/test/ELF/merge-align2.s

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[ELF] Allow placing non-string SHF_MERGE sections with different alignments into the same MergeSyntheticSection The difference from D63432/r365015 is that this patch does not place SHF_STRINGS sections with different alignments into the same MergeSyntheticSection. Doing that would: (1) create unnecessary padding and thus waste space. Add a test tail-merge-string-align2.s to check no extra padding is created. (2) make some input sections unaligned when tail merge (-O2) is enabled. The alignment of MergeTailAlignment::Builder was out of sync in D63432. MOVAPS on such unaligned strings can raise SIGSEGV. This should fix PR42289: the Linux kernel has a use case that input files have .rodata.cst32 sections with different alignments. The expectation (and what ld.bfd and gold do) is that in the -r link, there is only one .rodata.cst32 (SHF_MERGE sections with different alignments can be combined), but lld currently creates one for each different alignment. The current merging strategy: 1) Group SHF_MERGE sections by (name, sh_flags, sh_entsize and sh_addralign). Merging is performed among a group, even if -O0 is specified. 2) Create one output section for each group. This is a special case in addInputSec(). This patch changes 1) to: 1) Group SHF_MERGE sections by (name, sh_flags, sh_entsize). Merging is performed among a group, even if -O0 is specified. We will thus create just one .rodata.cst32 . This also improves merging efficiency when sections with the same name but different alignments are combined. Reviewed By: peter.smith Differential Revision: https://reviews.llvm.org/D64200 llvm-svn: 365139
2019-07-04 21:33:27 +08:00
# REQUIRES: x86
# RUN: llvm-mc -filetype=obj -triple=x86_64 %s -o %t.o
# RUN: ld.lld %t.o -o %t
# RUN: llvm-readelf -S %t | FileCheck --check-prefix=SEC %s
# RUN: llvm-readelf -x .cst8 %t | FileCheck %s
# RUN: ld.lld -O0 -r %t.o -o %t1.o
# RUN: llvm-readelf -S %t1.o | FileCheck --check-prefix=SEC %s
# RUN: llvm-readelf -x .cst8 %t1.o | FileCheck %s
## Check that if we have SHF_MERGE sections with the same name, flags and
## entsize, but different alignments, we combine them with the maximum input
## alignment as the output alignment.
# SEC: Name Type {{.*}} Size ES Flg Lk Inf Al
# SEC: .cst8 PROGBITS {{.*}} 000018 08 AM 0 0 8
# CHECK: 0x{{[0-9a-f]+}} 02000000 00000000 01000000 00000000
# CHECK-NEXT: 0x{{[0-9a-f]+}} 03000000 00000000
.section .cst8,"aM",@progbits,8,unique,0
.align 4
.quad 1
.quad 1
.section .cst8,"aM",@progbits,8,unique,1
.align 4
.quad 1
.quad 2
.section .cst8,"aM",@progbits,8,unique,2
.align 8
.quad 1
.quad 3