[PATCH] D21818: Add artificial debug information to avoid compiler crash

[David Blaikie via llvm-commits]

On Tue, Jun 28, 2016 at 3:28 PM, Yunzhong Gao via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> ygao created this revision.
> ygao added reviewers: aprantl, echristo, dblaikie.
> ygao added a subscriber: llvm-commits.
> Herald added a subscriber: mehdi_amini.
>
> Hi,
> The compiler crashed with the following test program:
>
> /* test.c
>  * To reproduce:
>  * $ clang -c -g -fstack-protector-strong test.c
>  * (fatal error: error in backend: Broken function found, compilation
> aborted!)
>  * (need  an assertion-enabled build of the compiler)
>  */
> void __stack_chk_fail(void) { return; }
>
> void foo() {
>   char bar[5];
> }
> /* end of test.c */
>
> This is not a legitimate input C file because __stack_chk_fail is a
> reserved function name.
>

Is there a legitimate case this fix addresses? Might be good to have such a
test case so we don't lose the coverage if/when this issue is fixed.

If there isn't, then perhaps we should fix the original issue (allowing
this invalid construct) rather than adding downstream workarounds?


> On the other hand, it seems that the compiler should be able to give a
> nicer diagnostic or
> otherwise fail more gracefully instead of having to crash on invalid input
> (in the spirit of all
> "internal compiler error"s are compiler bugs).
>
> The proposed patch here attempts to add artificial debug information when
> the compiler
> generates the call to __stack_chk_fail. Does this look like a reasonable
> thing to do?
>
> Many thanks in advance,
> - Gao
>
> http://reviews.llvm.org/D21818
>
> Files:
>   lib/CodeGen/StackProtector.cpp
>   test/CodeGen/X86/stack-protector.ll
>
> Index: test/CodeGen/X86/stack-protector.ll
> ===================================================================
> --- test/CodeGen/X86/stack-protector.ll
> +++ test/CodeGen/X86/stack-protector.ll
> @@ -3880,6 +3880,17 @@
>    ret i32 %call
>  }
>
> +define void @__stack_chk_fail() #1 !dbg !6 {
> +entry:
> +  ret void
> +}
> +
> +define void @test32() #1 !dbg !7 {
> +entry:
> +  %0 = alloca [5 x i8], align 1
> +  ret void
> +}
> +
>  declare double @testi_aux()
>  declare i8* @strcpy(i8*, i8*)
>  declare i32 @printf(i8*, ...)
> @@ -3899,3 +3910,16 @@
>  attributes #3 = { ssp "stack-protector-buffer-size"="33" }
>  attributes #4 = { ssp "stack-protector-buffer-size"="5" }
>  attributes #5 = { ssp "stack-protector-buffer-size"="6" }
> +
> +!llvm.dbg.cu = !{!0}
> +!llvm.module.flags = !{!3, !4}
> +!llvm.ident = !{!5}
> +
> +!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1)
> +!1 = !DIFile(filename: "test.c", directory: "/tmp")
> +!2 = !{}
> +!3 = !{i32 2, !"Dwarf Version", i32 4}
> +!4 = !{i32 2, !"Debug Info Version", i32 3}
> +!5 = !{!"clang version x.y.z"}
> +!6 = distinct !DISubprogram(name: "__stack_chk_fail", scope: !1, unit: !0)
> +!7 = distinct !DISubprogram(name: "foo", scope: !1, unit: !0)
> Index: lib/CodeGen/StackProtector.cpp
> ===================================================================
> --- lib/CodeGen/StackProtector.cpp
> +++ lib/CodeGen/StackProtector.cpp
> @@ -25,6 +25,7 @@
>  #include "llvm/IR/Attributes.h"
>  #include "llvm/IR/Constants.h"
>  #include "llvm/IR/DataLayout.h"
> +#include "llvm/IR/DebugInfo.h"
>  #include "llvm/IR/DerivedTypes.h"
>  #include "llvm/IR/Function.h"
>  #include "llvm/IR/GlobalValue.h"
> @@ -448,6 +449,7 @@
>    LLVMContext &Context = F->getContext();
>    BasicBlock *FailBB = BasicBlock::Create(Context,
> "CallStackCheckFailBlk", F);
>    IRBuilder<> B(FailBB);
> +  B.SetCurrentDebugLocation(DebugLoc::get(0, 0, F->getSubprogram()));
>    if (Trip.isOSOpenBSD()) {
>      Constant *StackChkFail =
>          M->getOrInsertFunction("__stack_smash_handler",
>
>
>
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