[PATCH] D95730: [MC] Support SHF_GNU_RETAIN as section flag 'R'

[Fangrui Song via Phabricator via llvm-commits]

MaskRay created this revision.
MaskRay added reviewers: arichardson, grimar, jhenderson, jrtc27.
Herald added subscribers: hiraditya, krytarowski.
MaskRay requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

GNU as sets EI_OSABI to ELFOSABI_GNU when SHF_GNU_RETAIN is used, even on
FreeBSD.

GNU ld respects SHF_GNU_RETAIN only for ELFOSABI_FREEBSD/ELFOSABI_GNU.
https://sourceware.org/bugzilla/show_bug.cgi?id=27282

MC doesn't set ELFOSABI_GNU for SHF_GNU_RETAIN/STB_GNU_UNIQUE/STT_GNU_IFUNC.
MC assembled object files do not have special semantics in GNU ld.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D95730

Files:
  llvm/lib/MC/MCParser/ELFAsmParser.cpp
  llvm/lib/MC/MCSectionELF.cpp
  llvm/test/MC/ELF/section-gnu.s


Index: llvm/test/MC/ELF/section-gnu.s
===================================================================
--- /dev/null
+++ llvm/test/MC/ELF/section-gnu.s
@@ -0,0 +1,16 @@
+# RUN: llvm-mc -triple=x86_64 %s | FileCheck %s --check-prefix=ASM
+# RUN: llvm-mc -filetype=obj -triple=x86_64 %s | llvm-readobj -hS - | FileCheck %s --check-prefix=OBJ
+
+# ASM: .section retain,"aR", at progbits
+
+## Note: GNU as sets OSABI to GNU.
+# OBJ:      OS/ABI: SystemV (0x0)
+
+# OBJ:      Name: retain
+# OBJ-NEXT: Type: SHT_PROGBITS
+# OBJ-NEXT: Flags [
+# OBJ-NEXT:   SHF_ALLOC
+# OBJ-NEXT:   SHF_GNU_RETAIN
+# OBJ-NEXT: ]
+
+.section retain,"aR", at progbits
Index: llvm/lib/MC/MCSectionELF.cpp
===================================================================
--- llvm/lib/MC/MCSectionELF.cpp
+++ llvm/lib/MC/MCSectionELF.cpp
@@ -102,6 +102,8 @@
     OS << 'T';
   if (Flags & ELF::SHF_LINK_ORDER)
     OS << 'o';
+  if (Flags & ELF::SHF_GNU_RETAIN)
+    OS << 'R';
 
   // If there are target-specific flags, print them.
   Triple::ArchType Arch = T.getArch();
Index: llvm/lib/MC/MCParser/ELFAsmParser.cpp
===================================================================
--- llvm/lib/MC/MCParser/ELFAsmParser.cpp
+++ llvm/lib/MC/MCParser/ELFAsmParser.cpp
@@ -326,6 +326,9 @@
     case 'G':
       flags |= ELF::SHF_GROUP;
       break;
+    case 'R':
+      flags |= ELF::SHF_GNU_RETAIN;
+      break;
     case '?':
       *UseLastGroup = true;
       break;


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