[MC] Improve COFF associative section lookup

Handle the case when the symbol is private. Private symbols are not in
the COFF object file symbol table, so they aren't inserted into
SymbolMap. We can't look up the section of the symbol that way. Instead,
get the MCSection from the MCSymbol and map that to the object file
section.

Print a better error message when the symbol has no section, like when
the symbol is undefined.

Fixes PR38607

llvm-svn: 339942

lib/MC/WinCOFFObjectWriter.cpp

@@ -1020,22 +1020,28 @@ uint64_t WinCOFFObjectWriter::writeObject(MCAssembler &Asm,
       continue;
 
     const MCSectionCOFF &MCSec = *Section->MCSection;
+    const MCSymbol *AssocMCSym = MCSec.getCOMDATSymbol();
+    assert(AssocMCSym);
 
-    const MCSymbol *COMDAT = MCSec.getCOMDATSymbol();
-    assert(COMDAT);
-    COFFSymbol *COMDATSymbol = GetOrCreateCOFFSymbol(COMDAT);
-    assert(COMDATSymbol);
-    COFFSection *Assoc = COMDATSymbol->Section;
-    if (!Assoc)
-      report_fatal_error(
-          Twine("Missing associated COMDAT section for section ") +
-          MCSec.getSectionName());
+    // It's an error to try to associate with an undefined symbol or a symbol
+    // without a section.
+    if (!AssocMCSym->isInSection()) {
+      Asm.getContext().reportError(
+          SMLoc(), Twine("cannot make section ") + MCSec.getSectionName() +
+                       Twine(" associative with sectionless symbol ") +
+                       AssocMCSym->getName());
+      continue;
+    }
+
+    const auto *AssocMCSec = cast<MCSectionCOFF>(&AssocMCSym->getSection());
+    assert(SectionMap.count(AssocMCSec));
+    COFFSection *AssocSec = SectionMap[AssocMCSec];
 
     // Skip this section if the associated section is unused.
-    if (Assoc->Number == -1)
+    if (AssocSec->Number == -1)
       continue;
 
-    Section->Symbol->Aux[0].Aux.SectionDefinition.Number = Assoc->Number;
+    Section->Symbol->Aux[0].Aux.SectionDefinition.Number = AssocSec->Number;
   }
 
   assignFileOffsets(Asm, Layout);

test/MC/COFF/assoc-private.s

@@ -0,0 +1,26 @@
+# RUN: llvm-mc -triple x86_64-pc-win32 -filetype=obj %s | llvm-objdump - -h -t | FileCheck %s
+
+# PR38607: We assemble this, and make .CRT$XCU comdat with .rdata even though
+# .rdata isn't comdat. It's not clear what the semantics are, but we assemble
+# it anyway.
+
+# CHECK: Sections:
+# CHECK: Idx Name          Size      Address          Type
+# CHECK:   3 .rdata        00000004 0000000000000000 DATA
+# CHECK:   4 .CRT$XCU      00000008 0000000000000000 DATA
+# CHECK: SYMBOL TABLE:
+# CHECK: [ 6](sec  4)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .rdata
+# CHECK: AUX scnlen 0x4 nreloc 0 nlnno 0 checksum 0x0 assoc 4 comdat 0
+# CHECK: [ 8](sec  5)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .CRT$XCU
+# CHECK: AUX scnlen 0x8 nreloc 1 nlnno 0 checksum 0x0 assoc 4 comdat 5
+# CHECK: [10](sec  0)(fl 0x00)(ty   0)(scl   2) (nx 0) 0x00000000 register_x
+
+	.section	.rdata,"dr"
+	.p2align	2               # @x
+.Lprivate:
+	.long	0                       # 0x0
+
+	.section	.CRT$XCU,"dr",associative,.Lprivate
+	.p2align	3
+	.quad	register_x
+

test/MC/COFF/assoc-undef.s

@@ -0,0 +1,8 @@
+# RUN: not llvm-mc %s -filetype=obj -triple=x86_64-windows-msvc -o /dev/null 2>&1 | FileCheck %s
+
+# CHECK: cannot make section assocSec associative with sectionless symbol undef
+
+	.section	assocSec,"dr",associative,undef
+	.p2align	3
+	.quad	my_initializer
+

test/MC/COFF/section-comdat.s

@@ -2,6 +2,8 @@
 // RUN: llvm-mc -triple x86_64-pc-win32 -filetype=obj %s | llvm-readobj -s -t | FileCheck %s
 
 .section assocSec, "dr", discard, "assocSym"
+.global assocSym
+assocSym:
 .long 1
 
 .section secName, "dr", discard, "Symbol1"