[llvm] r306057 - [MC] Allow assembling .secidx and .secrel32 for undefined symbols

[Reid Kleckner via llvm-commits]

Author: rnk
Date: Thu Jun 22 16:02:14 2017
New Revision: 306057

URL: http://llvm.org/viewvc/llvm-project?rev=306057&view=rev
Log:
[MC] Allow assembling .secidx and .secrel32 for undefined symbols

There's nothing incorrect about emitting such relocations against
symbols defined in other objects. The code in EmitCOFFSec* was missing
the visitUsedExpr part of MCStreamer::EmitValueImpl, so these symbols
were not being registered with the object file assembler.

This will be used to make reduced test cases for LLD.

Added:
    llvm/trunk/test/MC/COFF/secrel32-undef.s
Removed:
    llvm/trunk/test/MC/COFF/secidx-diagnostic.s
Modified:
    llvm/trunk/lib/MC/MCWinCOFFStreamer.cpp

Modified: llvm/trunk/lib/MC/MCWinCOFFStreamer.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/MC/MCWinCOFFStreamer.cpp?rev=306057&r1=306056&r2=306057&view=diff
==============================================================================
--- llvm/trunk/lib/MC/MCWinCOFFStreamer.cpp (original)
+++ llvm/trunk/lib/MC/MCWinCOFFStreamer.cpp Thu Jun 22 16:02:14 2017
@@ -190,7 +190,8 @@ void MCWinCOFFStreamer::EmitCOFFSafeSEH(
                    << COFF::SCT_COMPLEX_TYPE_SHIFT);
 }
 
-void MCWinCOFFStreamer::EmitCOFFSectionIndex(MCSymbol const *Symbol) {
+void MCWinCOFFStreamer::EmitCOFFSectionIndex(const MCSymbol *Symbol) {
+  visitUsedSymbol(*Symbol);
   MCDataFragment *DF = getOrCreateDataFragment();
   const MCSymbolRefExpr *SRE = MCSymbolRefExpr::create(Symbol, getContext());
   MCFixup Fixup = MCFixup::create(DF->getContents().size(), SRE, FK_SecRel_2);
@@ -198,8 +199,9 @@ void MCWinCOFFStreamer::EmitCOFFSectionI
   DF->getContents().resize(DF->getContents().size() + 2, 0);
 }
 
-void MCWinCOFFStreamer::EmitCOFFSecRel32(MCSymbol const *Symbol,
+void MCWinCOFFStreamer::EmitCOFFSecRel32(const MCSymbol *Symbol,
                                          uint64_t Offset) {
+  visitUsedSymbol(*Symbol);
   MCDataFragment *DF = getOrCreateDataFragment();
   // Create Symbol A for the relocation relative reference.
   const MCExpr *MCE = MCSymbolRefExpr::create(Symbol, getContext());

Removed: llvm/trunk/test/MC/COFF/secidx-diagnostic.s
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/MC/COFF/secidx-diagnostic.s?rev=306056&view=auto
==============================================================================
--- llvm/trunk/test/MC/COFF/secidx-diagnostic.s (original)
+++ llvm/trunk/test/MC/COFF/secidx-diagnostic.s (removed)
@@ -1,10 +0,0 @@
-// RUN: not llvm-mc -filetype=obj -triple i686-pc-win32 %s 2>%t
-// RUN: FileCheck %s < %t
-
-// CHECK: symbol 'bar' can not be undefined
-// CHECK: symbol 'baz' can not be undefined
-
-.data
-foo:
-        .secidx bar
-        .secidx baz

Added: llvm/trunk/test/MC/COFF/secrel32-undef.s
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/MC/COFF/secrel32-undef.s?rev=306057&view=auto
==============================================================================
--- llvm/trunk/test/MC/COFF/secrel32-undef.s (added)
+++ llvm/trunk/test/MC/COFF/secrel32-undef.s Thu Jun 22 16:02:14 2017
@@ -0,0 +1,30 @@
+# RUN: llvm-mc -filetype=obj -triple i686-pc-win32 %s -o %t.obj
+# RUN: llvm-readobj -symbols -relocations %t.obj | FileCheck %s
+
+# Previously .secrel32 and .secidx relocations against undefined symbols
+# resulted in an error. That was a mistake. The linker is fully capable of
+# resolving these relocations against symbols in other object files. Such
+# relocations can be found in the MSVCRT debug info describing linker-provided
+# symbols like __safe_se_handler_table and __guard_fids_table.
+
+.data
+foo:
+        .secrel32 bar
+        .secidx baz
+
+
+# CHECK: Relocations [
+# CHECK:   Section (2) .data {
+# CHECK:     0x0 IMAGE_REL_I386_SECREL bar
+# CHECK:     0x4 IMAGE_REL_I386_SECTION baz
+# CHECK:   }
+# CHECK: ]
+
+# CHECK:   Symbol {
+# CHECK:     Name: bar
+# CHECK-NEXT:     Value: 0
+# CHECK-NEXT:     Section: IMAGE_SYM_UNDEFINED (0)
+# CHECK:   Symbol {
+# CHECK:     Name: baz
+# CHECK-NEXT:     Value: 0
+# CHECK-NEXT:     Section: IMAGE_SYM_UNDEFINED (0)