[MC][X86] Allow SHT_PROGBITS for .eh_frame on x86-64

GNU as emits SHT_PROGBITS .eh_frame by default for .cfi_* directives.
We follow x86-64 psABI and use SHT_X86_64_UNWIND for .eh_frame

Don't error for SHT_PROGBITS .eh_frame on x86-64.
This keeps compatibility with `.section .eh_frame,"a",@progbits` in existing assembly files.

See https://groups.google.com/d/msg/x86-64-abi/7sr4E6THl3g/zUU2UPHOAQAJ
for more discussions.

Reviewed By: joerg

Differential Revision: https://reviews.llvm.org/D76151

Author: MaskRay

llvm/lib/MC/MCParser/ELFAsmParser.cpp

@@ -637,7 +637,11 @@ bool ELFAsmParser::ParseSectionArguments(bool IsPush, SMLoc loc) {
   MCSectionELF *Section = getContext().getELFSection(
       SectionName, Type, Flags, Size, GroupName, UniqueID, LinkedToSym);
   getStreamer().SwitchSection(Section, Subsection);
-  if (Section->getType() != Type)
+  // x86-64 psABI names SHT_X86_64_UNWIND as the canonical type for .eh_frame,
+  // but GNU as emits SHT_PROGBITS .eh_frame for .cfi_* directives. Don't error
+  // for SHT_PROGBITS .eh_frame
+  if (Section->getType() != Type &&
+      !(SectionName == ".eh_frame" && Type == ELF::SHT_PROGBITS))
     Error(loc, "changed section type for " + SectionName + ", expected: 0x" +
                    utohexstr(Section->getType()));
   if (Section->getFlags() != Flags)

llvm/test/MC/ELF/section-type-changed.s

@@ -9,3 +9,11 @@
 .pushsection .foo,"a",@nobits
 
 .pushsection .foo,"a",@progbits
+
+## GNU as emits SHT_PROGBITS .eh_frame for .cfi_* directives. Don't error.
+.section .eh_frame,"a",@progbits
+.section .eh_frame,"a",@unwind
+.pushsection .eh_frame,"a",@progbits
+
+# CHECK: {{.*}}.s:[[# @LINE+1]]:1: error: changed section type for .eh_frame, expected: 0x70000001
+.section .eh_frame,"a",@nobits