[PATCH] D14021: Added cfi instructions for correct CFA calculation in case when movpc instruction expands to call and pop

[Violeta Vukobrat via llvm-commits]

violetav created this revision.
violetav added a reviewer: rnk.
violetav added a subscriber: llvm-commits.
violetav set the repository for this revision to rL LLVM.

This fixes the issue of wrong CFA calculation in the following case:

   0x08048400 <+0>:	push   %ebx
   0x08048401 <+1>:	sub    $0x8,%esp
   0x08048404 <+4>:	**call   0x8048409 <test+9>**
   0x08048409 <+9>:	**pop    %eax**
   0x0804840a <+10>:	add    $0x1bf7,%eax
   0x08048410 <+16>:	mov    %eax,%ebx
   0x08048412 <+18>:	call   0x80483f0 <bar>
   0x08048417 <+23>:	add    $0x8,%esp
   0x0804841a <+26>:	pop    %ebx
   0x0804841b <+27>:	ret

The highlighted instructions are a product of movpc instruction. The **call** instruction changes the stack pointer, and **pop** instruction restores its value. However, the rule for computing CFA is not updated and is wrong on the **pop** instruction. So, e.g. backtrace in gdb doesn't work when on the pop instruction. This solution adds cfi instructions for both **call** and **pop** instructions.
** cfi_adjust_cfa_offset** instruction is used with the appropriate offset for setting the rules to calculate CFA correctly.

Repository:
  rL LLVM

http://reviews.llvm.org/D14021

Files:
  lib/CodeGen/AsmPrinter/AsmPrinterDwarf.cpp
  lib/Target/X86/X86MCInstLower.cpp
  test/CodeGen/X86/movpc32-check.ll

Index: test/CodeGen/X86/movpc32-check.ll
===================================================================
--- /dev/null
+++ test/CodeGen/X86/movpc32-check.ll
@@ -0,0 +1,42 @@
+; RUN: llc < %s -mtriple=i686-pc-linux -relocation-model=pic | FileCheck %s
+
+target datalayout = "e-m:e-p:32:32-f64:32:64-f80:32-n8:16:32-S128"
+target triple = "i686-pc-linux"
+
+; Function Attrs: nounwind
+define void @test() #0 {
+entry:
+  call void bitcast (void (...)* @bar to void ()*)(), !dbg !11
+  ret void, !dbg !12
+}
+
+declare void @bar(...) #1
+
+attributes #0 = { nounwind "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="i686" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="i686" "unsafe-fp-math"="false" "use-soft-float"="false" }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!7, !8, !9}
+!llvm.ident = !{!10}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 3.8.0 (http://llvm.org/git/clang.git 3490ab8630d5643f71f1f04e46984f05b27b8d67) (http://llvm.org/git/llvm.git d2643e2ff955ed234944fe3c6b4ffc1250085843)", isOptimized: false, runtimeVersion: 0, emissionKind: 1, enums: !2, subprograms: !3)
+!1 = !DIFile(filename: "test.c", directory: "movpc-test")
+!2 = !{}
+!3 = !{!4}
+!4 = distinct !DISubprogram(name: "test", scope: !1, file: !1, line: 2, type: !5, isLocal: false, isDefinition: true, scopeLine: 3, isOptimized: false, function: void ()* @test, variables: !2)
+!5 = !DISubroutineType(types: !6)
+!6 = !{null}
+!7 = !{i32 2, !"Dwarf Version", i32 4}
+!8 = !{i32 2, !"Debug Info Version", i32 3}
+!9 = !{i32 1, !"PIC Level", i32 2}
+!10 = !{!"clang version 3.8.0 (http://llvm.org/git/clang.git 3490ab8630d5643f71f1f04e46984f05b27b8d67) (http://llvm.org/git/llvm.git d2643e2ff955ed234944fe3c6b4ffc1250085843)"}
+!11 = !DILocation(line: 4, column: 3, scope: !4)
+!12 = !DILocation(line: 5, column: 1, scope: !4)
+
+; CHECK: calll .L0$pb
+; CHECK-NEXT: .Ltmp3:
+; CHECK-NEXT: .cfi_adjust_cfa_offset 4
+; CHECK-NEXT: .L0$pb:
+; CHECK-NEXT: popl
+; CHECK-NEXT: .Ltmp4:
+; CHECK-NEXT: .cfi_adjust_cfa_offset -4
Index: lib/Target/X86/X86MCInstLower.cpp
===================================================================
--- lib/Target/X86/X86MCInstLower.cpp
+++ lib/Target/X86/X86MCInstLower.cpp
@@ -1140,12 +1140,33 @@
     EmitAndCountInstruction(MCInstBuilder(X86::CALLpcrel32)
       .addExpr(MCSymbolRefExpr::create(PICBase, OutContext)));
 
+    const X86FrameLowering* FrameLowering =
+        MF->getSubtarget<X86Subtarget>().getFrameLowering();
+    bool hasFP = FrameLowering->hasFP(*MF);
+
+    bool NeedsDwarfCFI = MMI->hasDebugInfo();
+    int stackGrowth = -RI->getSlotSize();
+
+    if (NeedsDwarfCFI && !hasFP) {
+      unsigned CFIIndex = MMI->addFrameInst(
+          MCCFIInstruction::createAdjustCfaOffset(nullptr, -stackGrowth));
+      (void)CFIIndex;
+      OutStreamer->EmitCFIAdjustCfaOffset(-stackGrowth);
+    }
+
     // Emit the label.
     OutStreamer->EmitLabel(PICBase);
 
     // popl $reg
     EmitAndCountInstruction(MCInstBuilder(X86::POP32r)
                             .addReg(MI->getOperand(0).getReg()));
+
+    if (NeedsDwarfCFI && !hasFP) {
+      unsigned CFIIndex = MMI->addFrameInst(
+          MCCFIInstruction::createAdjustCfaOffset(nullptr, stackGrowth));
+      (void)CFIIndex;
+      OutStreamer->EmitCFIAdjustCfaOffset(stackGrowth);
+    }
     return;
   }
 
Index: lib/CodeGen/AsmPrinter/AsmPrinterDwarf.cpp
===================================================================
--- lib/CodeGen/AsmPrinter/AsmPrinterDwarf.cpp
+++ lib/CodeGen/AsmPrinter/AsmPrinterDwarf.cpp
@@ -240,6 +240,9 @@
   case MCCFIInstruction::OpEscape:
     OutStreamer->EmitCFIEscape(Inst.getValues());
     break;
+  case MCCFIInstruction::OpAdjustCfaOffset:
+    OutStreamer->EmitCFIAdjustCfaOffset(Inst.getOffset());
+    break;
   }
 }
 


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