[MC][COFF] Add COFF section flag "Info"

[bcl5980]

Summary

For now, we have not parse section flag Info in asm file. When we emit a section with info flag to asm, then compile asm to obj we will lose the Info flag for the section.
The motivation of this change is ARM64EC's hybmp$x section. If we lose the Info flag MSVC link will report a warning:
warning LNK4078: multiple '.hybmp' sections found with different attributes

[bcl5980]

Fix test.

[bcl5980]

Fix tests failure

[efriedma]

LGTM

[mstorsjo]

llvm/test/MC/COFF/section.s

40

Is this a section flag that GNU as also supports, or is this flag a new invention (which hopefully doesn’t collide with something elder in GNU as)?

[efriedma]

Actually, hmm, looking at this again, I think binutils uses "e" for this flag.

[bcl5980]

In D136125#3865895, @efriedma wrote:

Actually, hmm, looking at this again, I think binutils uses "e" for this flag.

It looks in llvm-nm, it use "i" for the flag.
https://github.com/llvm/llvm-project/blob/67957368ae9776ec25db80c69f772e40c75ed690/llvm/tools/llvm-nm/llvm-nm.cpp#L941

[efriedma]

So does binutils nm. But binutils as expects "e".

[bcl5980]

In D136125#3866684, @efriedma wrote:

So does binutils nm. But binutils as expects "e".

Can you provider some detail link for that? I try to search IMAGE_SCN_LNK_INFO in git://sourceware.org/git/binutils-gdb.git, but haven't find anything.

[efriedma]

Oh, sorry, I got confused. binutils apparently treats "e" as an alias for "n".

"i" doesn't appear to conflict with any existing usage, so should be fine.

[MaskRay]

llvm/test/MC/COFF/section.s

40

How can I configure binutils for Windows to check this?

[efriedma]

llvm/test/MC/COFF/section.s

40

Not sure what exactly you're asking, but possible answers:

• mingw gcc/binutils binary packages are widely available; you don't need to try to build it yourself.
• binutils source code does not refer to IMAGE_SCN_LNK_INFO anywhere relevant, and none of the documented flags produce it.
• binutils currently produces an error message if you try to use "i".

[mstorsjo]

llvm/test/MC/COFF/section.s

40

Debian/Ubuntu based linux distros provide binutils targeting mingw in packages named e.g. binutils-mingw-w64-x86-64 (and full toolchains pulled in by e.g. gcc-mingw-w64-x86-64). And you can build binutils yourself with e.g. ../binutils-gdb/configure --target=x86_64-w64-mingw32 --disable-werror --disable-gdb.

llvm/lib/MC/MCParser/COFFAsmParser.cpp

if (Flags & COFF::IMAGE_SCN_MEM_READ &&
       (Flags & COFF::IMAGE_SCN_MEM_WRITE) == 0)
     return SectionKind::getReadOnly();
   return SectionKind::getData();
 }
 
 bool COFFAsmParser::ParseSectionFlags(StringRef SectionName,
                                       StringRef FlagsString, unsigned *Flags) {
   enum {
-    None        = 0,
-    Alloc       = 1 << 0,
-    Code        = 1 << 1,
-    Load        = 1 << 2,
-    InitData    = 1 << 3,
-    Shared      = 1 << 4,
-    NoLoad      = 1 << 5,
-    NoRead      = 1 << 6,
-    NoWrite     = 1 << 7,
+    None = 0,
+    Alloc = 1 << 0,
+    Code = 1 << 1,
+    Load = 1 << 2,
+    InitData = 1 << 3,
+    Shared = 1 << 4,
+    NoLoad = 1 << 5,
+    NoRead = 1 << 6,
+    NoWrite = 1 << 7,
     Discardable = 1 << 8,
+    Info = 1 << 9,
   };
 
   bool ReadOnlyRemoved = false;
   unsigned SecFlags = None;
 
   for (char FlagChar : FlagsString) {
     switch (FlagChar) {
     case 'a':
case 'x': // executable section
       if (!ReadOnlyRemoved)
         SecFlags |= NoWrite;
       break;
 
     case 'y': // not readable
       SecFlags |= NoRead | NoWrite;
       break;
 
+    case 'i': // info
+      SecFlags |= Info;
+      break;
+
     default:
       return TokError("unknown flag");
     }
   }
 
   *Flags = 0;
 
   if (SecFlags == None)
if ((SecFlags & Discardable) ||
       MCSectionCOFF::isImplicitlyDiscardable(SectionName))
     *Flags |= COFF::IMAGE_SCN_MEM_DISCARDABLE;
   if ((SecFlags & NoRead) == 0)
     *Flags |= COFF::IMAGE_SCN_MEM_READ;
   if ((SecFlags & NoWrite) == 0)
     *Flags |= COFF::IMAGE_SCN_MEM_WRITE;
   if (SecFlags & Shared)
     *Flags |= COFF::IMAGE_SCN_MEM_SHARED;
+  if (SecFlags & Info)
+    *Flags |= COFF::IMAGE_SCN_LNK_INFO;
 
   return false;
 }
 
 /// ParseDirectiveSymbolAttribute
 ///  ::= { ".weak", ... } [ identifier ( , identifier )* ]
 bool COFFAsmParser::ParseDirectiveSymbolAttribute(StringRef Directive, SMLoc) {
   MCSymbolAttr Attr = StringSwitch<MCSymbolAttr>(Directive)

llvm/lib/MC/MCSectionCOFF.cpp

else
     OS << 'y';
   if (getCharacteristics() & COFF::IMAGE_SCN_LNK_REMOVE)
     OS << 'n';
   if (getCharacteristics() & COFF::IMAGE_SCN_MEM_SHARED)
     OS << 's';
   if ((getCharacteristics() & COFF::IMAGE_SCN_MEM_DISCARDABLE) &&
       !isImplicitlyDiscardable(getName()))
     OS << 'D';
+  if (getCharacteristics() & COFF::IMAGE_SCN_LNK_INFO)
+    OS << 'i';
   OS << '"';
 
   if (getCharacteristics() & COFF::IMAGE_SCN_LNK_COMDAT) {
     if (COMDATSymbol)
       OS << ",";
     else
       OS << "\n\t.linkonce\t";
     switch (Selection) {

llvm/test/MC/COFF/section.s

 .section s_d,"d"; .long 1
 .section s_D,"D"; .long 1
 .section s_n,"n"; .long 1
 .section s_r,"r"; .long 1
 .section s_s,"s"; .long 1
 .section s_w,"w"; .long 1
 .section s_x,"x"; .long 1
 .section s_y,"y"; .long 1
+.section s_y,"i"; .long 1
 
 // CHECK:        Section {
 // CHECK:          Name: s
 // CHECK:          Characteristics [
 // CHECK-NEXT:       IMAGE_SCN_ALIGN_1BYTES
 // CHECK-NEXT:       IMAGE_SCN_CNT_INITIALIZED_DATA
 // CHECK-NEXT:       IMAGE_SCN_MEM_READ
 // CHECK-NEXT:       IMAGE_SCN_MEM_WRITE

 // CHECK-NEXT:     ]
 // CHECK:        }
 // CHECK:        Section {
 // CHECK:          Name: s_y
 // CHECK:          Characteristics [
 // CHECK-NEXT:       IMAGE_SCN_ALIGN_1BYTES
 // CHECK-NEXT:     ]
 // CHECK:        }
+// CHECK:        Section {
+// CHECK:          Name: s_y
+// CHECK:          Characteristics [
+// CHECK-NEXT:       IMAGE_SCN_ALIGN_1BYTES
+// CHECK-NEXT:       IMAGE_SCN_LNK_INFO
+// CHECK-NEXT:     ]
+// CHECK:        }
 
 // w makes read-only to readable
 .section s_rw,"rw"; .long 1
 // CHECK:        Section {
 // CHECK:          Name: s_rw
 // CHECK:          Characteristics [
 // CHECK-NEXT:       IMAGE_SCN_ALIGN_1BYTES
 // CHECK-NEXT:       IMAGE_SCN_CNT_INITIALIZED_DATA