[PATCH] D153839: [XCOFF] Force recording a relocation for weak symbol label.

[Esme Yi via Phabricator via llvm-commits]

Esme created this revision.
Esme added reviewers: shchenz, hubert.reinterpretcast, anhtuyen, DiggerLin, w2yehia, stephenpeckham, PowerPC.
Herald added subscribers: kbarton, hiraditya, nemanjai.
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Esme requested review of this revision.
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Herald added a subscriber: llvm-commits.

Currently, if there are multiple definitions of the same symbol declared has weak linkage, the linker may choose the wrong one when they are compiled with integrated-as.
For example

  > cat t1.c 
  __attribute__((weak))
  __attribute__((noinline))
  int foo() { return 3; }
  
  int main() { return foo(); }
  
  > cat t2.c
  __attribute__((weak))
  int foo() {  return 1; }
  
  >  ~/Source/install.opt/bin/ibm-clang t2.c t1.c -fintegrated-as && ./a.out; echo $?
  3
  > ~/Source/install.opt/bin/ibm-clang t2.c t1.c -fno-integrated-as && ./a.out; echo $?
  1

This patch fixes the issue.
If the target symbol is a weak label we must not attempt to resolve the fixup directly.  Emit a relocation and leave resolution of the final target address to the linker.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D153839

Files:
  llvm/lib/MC/XCOFFObjectWriter.cpp
  llvm/lib/Target/PowerPC/MCTargetDesc/PPCAsmBackend.cpp
  llvm/test/CodeGen/PowerPC/aix-weak-reloc.ll


Index: llvm/test/CodeGen/PowerPC/aix-weak-reloc.ll
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/PowerPC/aix-weak-reloc.ll
@@ -0,0 +1,47 @@
+; RUN: llc -mtriple powerpc-ibm-aix-xcoff -filetype=obj -o %t.o < %s
+; RUN: llvm-objdump -dr %t.o | FileCheck --check-prefix=OBJ32 %s
+
+; RUN: llc -mtriple powerpc64-ibm-aix-xcoff -filetype=obj -o %t.o < %s
+; RUN: llvm-objdump -dr %t.o | FileCheck --check-prefix=OBJ64 %s
+
+; Function Attrs: noinline nounwind optnone
+define i32 @main() {
+entry:
+  %retval = alloca i32, align 4
+  store i32 0, ptr %retval, align 4
+  %call = call i32 @foo()
+  ret i32 %call
+}
+
+; Function Attrs: noinline nounwind optnone
+define weak i32 @foo() {
+entry:
+  ret i32 3
+}
+
+; OBJ32:       00000000 <.main>:
+; OBJ32-NEXT:         0: 7c 08 02 a6  	mflr 0
+; OBJ32-NEXT:         4: 94 21 ff c0  	stwu 1, -64(1)
+; OBJ32-NEXT:         8: 38 60 00 00  	li 3, 0
+; OBJ32-NEXT:         c: 90 01 00 48  	stw 0, 72(1)
+; OBJ32-NEXT:        10: 90 61 00 3c  	stw 3, 60(1)
+; OBJ32-NEXT:        14: 48 00 00 31  	bl 0x44 <.foo>
+; OBJ32-NEXT:  			00000014:  R_RBR	.foo
+; OBJ32-NEXT:        18: 60 00 00 00  	nop
+; OBJ32:       00000044 <.foo>:
+; OBJ32-NEXT:        44: 38 60 00 03  	li 3, 3
+; OBJ32-NEXT:        48: 4e 80 00 20  	blr
+
+; OBJ64:      0000000000000000 <.main>:
+; OBJ64-NEXT:        0: 7c 08 02 a6  	mflr 0
+; OBJ64-NEXT:        4: f8 21 ff 81  	stdu 1, -128(1)
+; OBJ64-NEXT:        8: 38 60 00 00  	li 3, 0
+; OBJ64-NEXT:        c: f8 01 00 90  	std 0, 144(1)
+; OBJ64-NEXT:       10: 90 61 00 7c  	stw 3, 124(1)
+; OBJ64-NEXT:       14: 48 00 00 31  	bl 0x44 <.foo>
+; OBJ64-NEXT: 		0000000000000014:  R_RBR	.foo
+; OBJ64-NEXT:       18: 60 00 00 00  	nop
+; OBJ64:      0000000000000044 <.foo>:
+; OBJ64-NEXT:       44: 38 60 00 03  	li 3, 3
+; OBJ64-NEXT:       48: 4e 80 00 20  	blr
+
Index: llvm/lib/Target/PowerPC/MCTargetDesc/PPCAsmBackend.cpp
===================================================================
--- llvm/lib/Target/PowerPC/MCTargetDesc/PPCAsmBackend.cpp
+++ llvm/lib/Target/PowerPC/MCTargetDesc/PPCAsmBackend.cpp
@@ -19,6 +19,7 @@
 #include "llvm/MC/MCSectionMachO.h"
 #include "llvm/MC/MCSubtargetInfo.h"
 #include "llvm/MC/MCSymbolELF.h"
+#include "llvm/MC/MCSymbolXCOFF.h"
 #include "llvm/MC/MCValue.h"
 #include "llvm/MC/TargetRegistry.h"
 #include "llvm/Support/ErrorHandling.h"
@@ -178,7 +179,10 @@
           unsigned Other = S->getOther() << 2;
           if ((Other & ELF::STO_PPC64_LOCAL_MASK) != 0)
             return true;
-        }
+        } else if (const auto *S = dyn_cast<MCSymbolXCOFF>(&A->getSymbol())) {
+          return !Target.isAbsolute() && S->isExternal() &&
+                 S->getStorageClass() == XCOFF::C_WEAKEXT;
+       }
       }
       return false;
     }
Index: llvm/lib/MC/XCOFFObjectWriter.cpp
===================================================================
--- llvm/lib/MC/XCOFFObjectWriter.cpp
+++ llvm/lib/MC/XCOFFObjectWriter.cpp
@@ -730,10 +730,10 @@
     // address, fragment offset and Fixup offset.
     uint64_t BRInstrAddress =
         SectionMap[ParentSec]->Address + FixupOffsetInCsect;
-    // The FixedValue should be the difference between SymA csect address and BR
-    // instr address plus any constant value.
-    FixedValue =
-        SectionMap[SymASec]->Address - BRInstrAddress + Target.getConstant();
+    // The FixedValue should be the difference between symbol's virtual address
+    // and BR instr address plus any constant value.
+    FixedValue = getVirtualAddress(SymA, SymASec) - BRInstrAddress +
+                 Target.getConstant();
   } else if (Type == XCOFF::RelocationType::R_REF) {
     // The FixedValue and FixupOffsetInCsect should always be 0 since it
     // specifies a nonrelocating reference.


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