Change section flag character for SHF_LINK_ORDER to "o"

[eugenis]

Summary

GAS uses "m" as a compatibility alias for "M" (SHF_MERGE).

"o" is free, except on ia64, where it already means SHF_LINK_ORDER.

[pcc]

Looks reasonable, but Rafael should take a look as well.

Please also update docs/Extensions.rst. I know that you are working on adding this feature to GNU as, but we should probably keep the extension docs up to date until that change lands.

[eugenis]

Docs updated.

[• rafael]

LGTM

[eugenis]

r299479
Thanks!

docs/Extensions.rst

.. code-block:: gas
 
   .section  .text,"ax",@progbits,unique,2
         nop
 
 
 The unique number is not present in the resulting object at all. It is just used
 in the assembler to differentiate the sections.
 
-The 'm' flag is mapped to SHF_LINK_ORDER. If it is present, a symbol
+The 'o' flag is mapped to SHF_LINK_ORDER. If it is present, a symbol
 must be given that identifies the section to be placed is the
 .sh_link.
 
 .. code-block:: gas
 
         .section .foo,"a",@progbits
         .Ltmp:
-        .section .bar,"am",@progbits,.Ltmp
+        .section .bar,"ao",@progbits,.Ltmp
 
 which is equivalent to just
 
 .. code-block:: gas
 
         .section .foo,"a",@progbits
-        .section .bar,"am",@progbits,.foo
+        .section .bar,"ao",@progbits,.foo
 
 
 Target Specific Behaviour
 =========================
 
 X86
 ---
 

lib/MC/MCParser/ELFAsmParser.cpp

case 'e':
       flags |= ELF::SHF_EXCLUDE;
       break;
     case 'x':
       flags |= ELF::SHF_EXECINSTR;
       break;
     case 'w':
       flags |= ELF::SHF_WRITE;
       break;
-    case 'm':
+    case 'o':
       flags |= ELF::SHF_LINK_ORDER;
       break;
     case 'M':
       flags |= ELF::SHF_MERGE;
       break;
     case 'S':
       flags |= ELF::SHF_STRINGS;
       break;

lib/MC/MCSectionELF.cpp

if (Flags & ELF::SHF_WRITE)
     OS << 'w';
   if (Flags & ELF::SHF_MERGE)
     OS << 'M';
   if (Flags & ELF::SHF_STRINGS)
     OS << 'S';
   if (Flags & ELF::SHF_TLS)
     OS << 'T';
   if (Flags & ELF::SHF_LINK_ORDER)
-    OS << 'm';
+    OS << 'o';
 
   // If there are target-specific flags, print them.
   Triple::ArchType Arch = T.getArch();
   if (Arch == Triple::xcore) {
     if (Flags & ELF::XCORE_SHF_CP_SECTION)
       OS << 'c';
     if (Flags & ELF::XCORE_SHF_DP_SECTION)
       OS << 'd';

test/CodeGen/X86/elf-associated.ll

 ; RUN: llc -data-sections=1 -mtriple x86_64-pc-linux-gnu < %s | FileCheck %s
 ; RUN: llc -data-sections=0 -mtriple x86_64-pc-linux-gnu < %s | FileCheck %s
 
 @a = global i32 1
 @b = global i32 2, !associated !0
 !0 = !{i32* @a}
-; CHECK-DAG: .section .data.b,"awm",@progbits,a
+; CHECK-DAG: .section .data.b,"awo",@progbits,a
 
 ; Loop is OK. Also, normally -data-sections=0 would place @c and @d in the same section. !associated prevents that.
 @c = global i32 2, !associated !2
 @d = global i32 2, !associated !1
 !1 = !{i32* @c}
 !2 = !{i32* @d}
-; CHECK-DAG: .section .data.c,"awm",@progbits,d
-; CHECK-DAG: .section .data.d,"awm",@progbits,c
+; CHECK-DAG: .section .data.c,"awo",@progbits,d
+; CHECK-DAG: .section .data.d,"awo",@progbits,c
 
 ; BSS is OK.
 @e = global i32 0
 @f = global i32 0, !associated !3
 @g = global i32 1, !associated !3
 !3 = !{i32* @e}
-; CHECK-DAG: .section .bss.f,"awm",@nobits,e
-; CHECK-DAG: .section .data.g,"awm",@progbits,e
+; CHECK-DAG: .section .bss.f,"awo",@nobits,e
+; CHECK-DAG: .section .data.g,"awo",@progbits,e
 
 ; Explicit sections.
 @h = global i32 1, section "aaa"
 @i = global i32 1, section "bbb", !associated !4
 @j = global i32 1, section "bbb", !associated !4
 @k = global i32 1, !associated !4
 !4 = !{i32* @h}
 ; CHECK-DAG: .section aaa,"aw",@progbits
-; CHECK-DAG: .section bbb,"awm",@progbits,h,unique,1
-; CHECK-DAG: .section bbb,"awm",@progbits,h,unique,2
-; CHECK-DAG: .section .data.k,"awm",@progbits,h
+; CHECK-DAG: .section bbb,"awo",@progbits,h,unique,1
+; CHECK-DAG: .section bbb,"awo",@progbits,h,unique,2
+; CHECK-DAG: .section .data.k,"awo",@progbits,h
 
 ; Non-GlobalObject metadata.
 @l = global i32 1, section "ccc", !associated !5
 !5 = !{i32* null}
 ; CHECK-DAG: .section ccc,"aw",@progbits

test/MC/ELF/section-metadata-err1.s

 // RUN: not llvm-mc -triple x86_64-pc-linux-gnu %s -o - 2>&1 | FileCheck %s
 
 // CHECK: error: symbol is not in a section: foo
 
-        .section .shf_metadata,"am",@progbits,foo
+        .section .shf_metadata,"ao",@progbits,foo

test/MC/ELF/section-metadata-err2.s

 // RUN: not llvm-mc -triple x86_64-pc-linux-gnu %s -o - 2>&1 | FileCheck %s
 
 // CHECK: error: symbol is not in a section: foo
 
         .quad foo
-        .section .shf_metadata,"am",@progbits,foo
+        .section .shf_metadata,"ao",@progbits,foo

test/MC/ELF/section-metadata-err3.s

 // RUN: not llvm-mc -triple x86_64-pc-linux-gnu %s -o - 2>&1 | FileCheck %s
 
 // CHECK: error: symbol is not in a section: foo
 
         foo = 42
-        .section .shf_metadata,"am",@progbits,foo
+        .section .shf_metadata,"ao",@progbits,foo

test/MC/ELF/section-metadata-err4.s

 // RUN: not llvm-mc -triple x86_64-pc-linux-gnu %s -o - 2>&1 | FileCheck %s
 
 // CHECK: error: expected metadata symbol
 
-        .section .shf_metadata,"am",@progbits
+        .section .shf_metadata,"ao",@progbits

test/MC/ELF/section.s

.section .shf_metadata_target1, "a"
         .quad 0
 .section .shf_metadata_target2, "a", @progbits, unique, 1
 .Lshf_metadata_target2_1:
         .quad 0
 .section .shf_metadata_target2, "a", @progbits, unique, 2
 .Lshf_metadata_target2_2:
         .quad 0
 
-.section .shf_metadata1,"am",@progbits,.Lshf_metadata_target2_1
-.section .shf_metadata2,"am",@progbits,.Lshf_metadata_target2_2
-.section .shf_metadata3,"am",@progbits,.shf_metadata_target1
-// ASM: .section .shf_metadata1,"am",@progbits,.Lshf_metadata_target2_1
-// ASM: .section .shf_metadata2,"am",@progbits,.Lshf_metadata_target2_2
-// ASM: .section .shf_metadata3,"am",@progbits,.shf_metadata_target1
+.section .shf_metadata1,"ao",@progbits,.Lshf_metadata_target2_1
+.section .shf_metadata2,"ao",@progbits,.Lshf_metadata_target2_2
+.section .shf_metadata3,"ao",@progbits,.shf_metadata_target1
+// ASM: .section .shf_metadata1,"ao",@progbits,.Lshf_metadata_target2_1
+// ASM: .section .shf_metadata2,"ao",@progbits,.Lshf_metadata_target2_2
+// ASM: .section .shf_metadata3,"ao",@progbits,.shf_metadata_target1
 
 // CHECK:      Section {
 // CHECK:        Index: 22
 // CHECK-NEXT:   Name: .shf_metadata_target1
 
 // CHECK:      Section {
 // CHECK:        Index: 23
 // CHECK-NEXT:   Name: .shf_metadata_target2