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

[MaskRay]

Summary

Similar to 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.

[grimar]

I've added @jhenderson. who might be interested in .stack_sizes related changes too I guess.

[jhenderson]

Thanks, LGTM too. Honestly, I'm slightly surprised this wasn't already the case. I guess no-unique-section-names hasn't been widely used in practice.

[grimar]

LGTM

[MaskRay]

In D92151#2417868, @jhenderson wrote:

Thanks, LGTM too. Honestly, I'm slightly surprised this wasn't already the case. I guess no-unique-section-names hasn't been widely used in practice.

It hasn't been widely used in practice. GCC does not support -fno-unique-section-names (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95095)

llvm/lib/MC/MCObjectFileInfo.cpp

MCObjectFileInfo::getStackSizesSection(const MCSection &TextSec) const {
   unsigned Flags = ELF::SHF_LINK_ORDER;
   StringRef GroupName;
   if (const MCSymbol *Group = ElfSec.getGroup()) {
     GroupName = Group->getName();
     Flags |= ELF::SHF_GROUP;
   }
 
   return Ctx->getELFSection(".stack_sizes", ELF::SHT_PROGBITS, Flags, 0,
-                            GroupName, MCSection::NonUniqueID,
+                            GroupName, ElfSec.getUniqueID(),
                             cast<MCSymbolELF>(TextSec.getBeginSymbol()));
 }
 
 MCSection *
 MCObjectFileInfo::getBBAddrMapSection(const MCSection &TextSec) const {
   if (Env != IsELF)
     return nullptr;
 

llvm/test/CodeGen/X86/stack-size-section-function-sections.ll

-; 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",@progbits
-; CHECK: .section        .stack_sizes,"o",@progbits,.text._Z3barv{{$}}
-; CHECK: .section        .text._Z3foov,"ax",@progbits
-; CHECK: .section        .stack_sizes,"o",@progbits,.text._Z3foov{{$}}
+; UNIQ:   .section        .text._Z3barv,"ax",@progbits{{$}}
+; UNIQ:   .section        .stack_sizes,"o",@progbits,.text._Z3barv{{$}}
+; UNIQ:   .section        .text._Z3foov,"ax",@progbits{{$}}
+; UNIQ:   .section        .stack_sizes,"o",@progbits,.text._Z3foov{{$}}
+; NOUNIQ: .section        .text,"ax",@progbits,unique,1
+; NOUNIQ: .section        .stack_sizes,"o",@progbits,.text,unique,1
+; NOUNIQ: .section        .text,"ax",@progbits,unique,2
+; NOUNIQ: .section        .stack_sizes,"o",@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",@progbits,_Z4fooTIiET_v,comdat
-; CHECK: .section        .stack_sizes,"Go",@progbits,_Z4fooTIiET_v,comdat,.text._Z4fooTIiET_v{{$}}
+; UNIQ:   .section        .text._Z4fooTIiET_v,"axG",@progbits,_Z4fooTIiET_v,comdat{{$}}
+; UNIQ:   .section        .stack_sizes,"Go",@progbits,_Z4fooTIiET_v,comdat,.text._Z4fooTIiET_v{{$}}
+; NOUNIQ: .section        .text,"axG",@progbits,_Z4fooTIiET_v,comdat,unique,3
+; NOUNIQ: .section        .stack_sizes,"Go",@progbits,_Z4fooTIiET_v,comdat,.text,unique,3
 
 $_Z4fooTIiET_v = comdat any
 
 define dso_local i32 @_Z3barv() {
   ret i32 0
 }
 
 define dso_local i32 @_Z3foov() {
   %1 = call i32 @_Z4fooTIiET_v()
   ret i32 %1
 }
 
 define linkonce_odr dso_local i32 @_Z4fooTIiET_v() comdat {
   ret i32 0
 }