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From: "i at maskray dot me" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug debug/109591] New: Multiple -fdebug-prefix-map= prefixes match,
 which one wins?
Date: Fri, 21 Apr 2023 22:58:24 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109591

            Bug ID: 109591
           Summary: Multiple -fdebug-prefix-map=3D prefixes match, which one
                    wins?
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: debug
          Assignee: unassigned at gcc dot gnu.org
          Reporter: i at maskray dot me
  Target Milestone: ---

mkdir -p a/b/c
echo 'int main(){}' > a/b/c/d.c
~/Dev/gcc/out/release/gcc/xgcc -B ~/Dev/gcc/out/release/gcc -g -c
-fdebug-prefix-map=3Da/b/c=3Dz -fdebug-prefix-map=3Da/b=3Dy -fdebug-prefix-=
map=3Da=3Dx
a/b/c/d.c
objdump -Wi d.o | grep 'd\.c'  # <12>   DW_AT_name        : (indirect line
string, offset: 0): x/b/c/d.c
~/Dev/gcc/out/release/gcc/xgcc -B ~/Dev/gcc/out/release/gcc -g -c
-fdebug-prefix-map=3Da=3Dx -fdebug-prefix-map=3Da/b=3Dy -fdebug-prefix-map=
=3Da/b/c=3Dz
a/b/c/d.c
objdump -Wi d.o | grep 'd\.c'  # <12>   DW_AT_name        : (indirect line
string, offset: 0): z/d.c
return

When multiple -fdebug-prefix-map=3D options are applicable, it seems that t=
he
last wins.
In Clang, after https://reviews.llvm.org/D49466 (landed in Nov 2019), the
longest prefix wins.

clang -g -c -fdebug-prefix-map=3Da=3Dx -fdebug-prefix-map=3Da/b=3Dy
-fdebug-prefix-map=3Da/b/c=3Dz a/b/c/d.c # z/d.c
clang -g -c -fdebug-prefix-map=3Da=3Dx -fdebug-prefix-map=3Da/b=3Dy
-fdebug-prefix-map=3Da/b/c=3Dz a/b/c/d.c # z/d.c

This issue is motivated by https://reviews.llvm.org/D148757

---

Related, there is a strange use case where the old prefix is empty. The new
prefix may or may not end with a slash: '-fdebug-prefix-map=3D=3Dw' and
'-fdebug-prefix-map=3D=3Dw/'.

'-fdebug-prefix-map=3D=3Dw' changes the file name to wa/b/c/d.c . I am unsu=
re
whether it should be w/a/b/c/d.c instead. Clang has the same problem.=