[llvm-dev] Understanding how to use of debugger intrinsic functions (original) (raw)

Peng Yu via llvm-dev llvm-dev at lists.llvm.org
Mon Jan 28 16:36:36 PST 2019

I see debugger intrinsic functions like @llvm.dbg.declare appear in the .ll generated with -g. But I still don't understand how it is used.

https://llvm.org/docs/SourceLevelDebugging.html#debugger-intrinsic-functions

For the following C program, I got the relevant text in the .ll file pasted below and the relevant metadata (listed using depth-first search).

Does @llvm.dbg.declare actually translate to some machine code similar to other user-defined functions? It seems that it only describes the data types. Will they be translated to a native debugging format to store along with the executable?

Can they be used for binary instrumentations? Thanks.

////// #include <stdio.h>

int f(int i) { return i + 1; }

int main(int argc, char *argv[1]) { if(f(argc)) { puts("Hello World!"); } return 0; } //////

define i32 @main(i32 %arg, i8** %arg1) #0 !dbg !17 { ... store i32 %arg, i32* %tmp2, align 4 call void @llvm.dbg.declare(metadata i32* %tmp2, metadata !23, metadata !DIExpression()), !dbg !24 ...

!23 = !DILocalVariable(name: "argc", arg: 1, scope: !17, file: !1, line: 8, type: !11)

!17 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 8, type: !18, isLocal: false, isDefinition: true, scopeLine: 8, flags: DIFlagPrototyped, isOptimized: false, unit: !0, retainedNodes: !2) !1 = !DIFile(filename: "../test_data/main.c", directory: "/Users/pengy/linux/bin/wrappercomposite/src/xplat/llvmxplat/src/lvll2/lvll2fundbi/llin2funbodyraw0/main") !18 = !DISubroutineType(types: !19) !19 = !{!11, !11, !20} !11 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed) !20 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !21, size: 64) !21 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !22, size: 64) !22 = !DIBasicType(name: "char", size: 8, encoding: DW_ATE_signed_char)

!24 = !DILocation(line: 8, column: 14, scope: !17)

-- Regards, Peng

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