[PATCH] D92151: [MC] Set the unique id of .stack_sizes to the associated .text section's

Fangrui Song via Phabricator via llvm-commits llvm-commits at lists.llvm.org
Wed Nov 25 21:13:37 PST 2020

MaskRay created this revision.
MaskRay added reviewers: grimar, rahmanl, tmsriram.
Herald added subscribers: llvm-commits, pengfei, hiraditya.
Herald added a project: LLVM.
MaskRay requested review of this revision.

Similar to D92113 <https://reviews.llvm.org/D92113>. Currently `clang -fstack-size-section
-fno-unique-section-names` sets the linked-to symbol to the first
`.text`, which is:

- incorrect for COMDAT sections
- inferior for non-COMDAT sections in -ffunction-sections mode (poor

--gc-sections: .stack_sizes cannot be separately discarded)

Note, if the section symbol can be referenced in more places (if the
function begin symbol does not apply), we probably should consider
defining a different BeginSymbol for sections with ",unique" linkage.

  rG LLVM Github Monorepo



Index: llvm/test/CodeGen/X86/stack-size-section-function-sections.ll
--- llvm/test/CodeGen/X86/stack-size-section-function-sections.ll
+++ llvm/test/CodeGen/X86/stack-size-section-function-sections.ll
@@ -1,14 +1,23 @@
-; RUN: llc < %s -mtriple=x86_64-linux -stack-size-section -function-sections | FileCheck %s
+; RUN: llc < %s -mtriple=x86_64-linux -stack-size-section -function-sections | \
+; RUN:   FileCheck %s --check-prefix=UNIQ
+; RUN: llc < %s -mtriple=x86_64-linux -stack-size-section -function-sections -unique-section-names=0 | \
+; RUN:   FileCheck %s --check-prefix=NOUNIQ
 ; Check we add SHF_LINK_ORDER for .stack_sizes and link it with the corresponding .text sections.
-; CHECK: .section        .text._Z3barv,"ax", at progbits
-; CHECK: .section        .stack_sizes,"o", at progbits,.text._Z3barv{{$}}
-; CHECK: .section        .text._Z3foov,"ax", at progbits
-; CHECK: .section        .stack_sizes,"o", at progbits,.text._Z3foov{{$}}
+; UNIQ:   .section        .text._Z3barv,"ax", at progbits{{$}}
+; UNIQ:   .section        .stack_sizes,"o", at progbits,.text._Z3barv{{$}}
+; UNIQ:   .section        .text._Z3foov,"ax", at progbits{{$}}
+; UNIQ:   .section        .stack_sizes,"o", at progbits,.text._Z3foov{{$}}
+; NOUNIQ: .section        .text,"ax", at progbits,unique,1
+; NOUNIQ: .section        .stack_sizes,"o", at progbits,.text,unique,1
+; NOUNIQ: .section        .text,"ax", at progbits,unique,2
+; NOUNIQ: .section        .stack_sizes,"o", at progbits,.text,unique,2
 ; Check we add .stack_size section to a COMDAT group with the corresponding .text section if such a COMDAT exists.
-; CHECK: .section        .text._Z4fooTIiET_v,"axG", at progbits,_Z4fooTIiET_v,comdat
-; CHECK: .section        .stack_sizes,"Go", at progbits,_Z4fooTIiET_v,comdat,.text._Z4fooTIiET_v{{$}}
+; UNIQ:   .section        .text._Z4fooTIiET_v,"axG", at progbits,_Z4fooTIiET_v,comdat{{$}}
+; UNIQ:   .section        .stack_sizes,"Go", at progbits,_Z4fooTIiET_v,comdat,.text._Z4fooTIiET_v{{$}}
+; NOUNIQ: .section        .text,"axG", at progbits,_Z4fooTIiET_v,comdat,unique,3
+; NOUNIQ: .section        .stack_sizes,"Go", at progbits,_Z4fooTIiET_v,comdat,.text,unique,3
 $_Z4fooTIiET_v = comdat any
Index: llvm/lib/MC/MCObjectFileInfo.cpp
--- llvm/lib/MC/MCObjectFileInfo.cpp
+++ llvm/lib/MC/MCObjectFileInfo.cpp
@@ -997,7 +997,7 @@
   return Ctx->getELFSection(".stack_sizes", ELF::SHT_PROGBITS, Flags, 0,
-                            GroupName, MCSection::NonUniqueID,
+                            GroupName, ElfSec.getUniqueID(),

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