[lld] r367836 - [COFF] Omit automatically imported symbols from the symbol table

[Hans Wennborg via llvm-commits]

Merged to release_90 in r367986.

On Mon, Aug 5, 2019 at 1:56 PM Martin Storsjo via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
>
> Author: mstorsjo
> Date: Mon Aug  5 04:57:00 2019
> New Revision: 367836
>
> URL: http://llvm.org/viewvc/llvm-project?rev=367836&view=rev
> Log:
> [COFF] Omit automatically imported symbols from the symbol table
>
> These symbols actually point to the symbol's IAT entry, which
> obviously is different from the symbol itself (which is imported
> from a different module and doesn't exist in the current one).
>
> Omitting this symbol helps gdb inspect automatically imported
> symbols, see https://sourceware.org/bugzilla/show_bug.cgi?id=24574
> for discussion on the matter.
>
> Surprisingly, those extra symbols don't seem to be an issue for
> gdb when the sources have been built with clang, only with gcc.
> The actual logic in gdb that this depends on still is unknown, but
> omitting these symbols from the symbol table is the right thing to
> do in any case.
>
> Differential Revision: https://reviews.llvm.org/D65727
>
> Modified:
>     lld/trunk/COFF/Writer.cpp
>     lld/trunk/test/COFF/autoimport-gnu-implib.s
>     lld/trunk/test/COFF/autoimport-x86.s
>
> Modified: lld/trunk/COFF/Writer.cpp
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/COFF/Writer.cpp?rev=367836&r1=367835&r2=367836&view=diff
> ==============================================================================
> --- lld/trunk/COFF/Writer.cpp (original)
> +++ lld/trunk/COFF/Writer.cpp Mon Aug  5 04:57:00 2019
> @@ -1095,6 +1095,13 @@ Optional<coff_symbol16> Writer::createSy
>    }
>    }
>
> +  // Symbols that are runtime pseudo relocations don't point to the actual
> +  // symbol data itself (as they are imported), but points to the IAT entry
> +  // instead. Avoid emitting them to the symbol table, as they can confuse
> +  // debuggers.
> +  if (def->isRuntimePseudoReloc)
> +    return None;
> +
>    StringRef name = def->getName();
>    if (name.size() > COFF::NameSize) {
>      sym.Name.Offset.Zeroes = 0;
>
> Modified: lld/trunk/test/COFF/autoimport-gnu-implib.s
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/COFF/autoimport-gnu-implib.s?rev=367836&r1=367835&r2=367836&view=diff
> ==============================================================================
> --- lld/trunk/test/COFF/autoimport-gnu-implib.s (original)
> +++ lld/trunk/test/COFF/autoimport-gnu-implib.s Mon Aug  5 04:57:00 2019
> @@ -7,9 +7,10 @@
>  # RUN: llvm-ar rcs %t-implib.a %t-dabcdh.o %t-dabcds00000.o %t-dabcdt.o
>
>  # RUN: llvm-mc -triple=x86_64-windows-gnu %s -filetype=obj -o %t.obj
> -# RUN: lld-link -lldmingw -out:%t.exe -entry:main %t.obj %t-implib.a -verbose
> +# RUN: lld-link -lldmingw -debug:symtab -out:%t.exe -entry:main %t.obj %t-implib.a -verbose
>
>  # RUN: llvm-readobj --coff-imports %t.exe | FileCheck -check-prefix=IMPORTS %s
> +# RUN: llvm-nm %t.exe | FileCheck -check-prefix=SYMBOLS %s
>
>  # IMPORTS: Import {
>  # IMPORTS-NEXT: Name: foo.dll
> @@ -18,6 +19,10 @@
>  # IMPORTS-NEXT: Symbol: data (0)
>  # IMPORTS-NEXT: }
>
> +# Check that the automatically imported symbol "data" is not listed in
> +# the symbol table.
> +# SYMBOLS-NOT: {{ }}data
> +
>      .global main
>      .text
>  main:
>
> Modified: lld/trunk/test/COFF/autoimport-x86.s
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/COFF/autoimport-x86.s?rev=367836&r1=367835&r2=367836&view=diff
> ==============================================================================
> --- lld/trunk/test/COFF/autoimport-x86.s (original)
> +++ lld/trunk/test/COFF/autoimport-x86.s Mon Aug  5 04:57:00 2019
> @@ -5,11 +5,12 @@
>  # RUN: lld-link -out:%t-lib.dll -dll -entry:DllMainCRTStartup %t-lib.obj -lldmingw -implib:%t-lib.lib
>
>  # RUN: llvm-mc -triple=x86_64-windows-gnu %s -filetype=obj -o %t.obj
> -# RUN: lld-link -lldmingw -out:%t.exe -entry:main %t.obj %t-lib.lib -verbose
> +# RUN: lld-link -lldmingw -debug:symtab -out:%t.exe -entry:main %t.obj %t-lib.lib -verbose
>
>  # RUN: llvm-readobj --coff-imports %t.exe | FileCheck -check-prefix=IMPORTS %s
>  # RUN: llvm-objdump -d %t.exe | FileCheck -check-prefix=DISASM %s
>  # RUN: llvm-objdump -s %t.exe | FileCheck -check-prefix=CONTENTS %s
> +# RUN: llvm-nm %t.exe | FileCheck -check-prefix=SYMBOLS %s
>
>  # IMPORTS: Import {
>  # IMPORTS-NEXT: Name: autoimport-x86.s.tmp-lib.dll
> @@ -20,7 +21,7 @@
>
>  # DISASM: Disassembly of section .text:
>  # DISASM-EMPTY:
> -# DISASM: .text:
> +# DISASM: main:
>  # Relative offset at 0x1002 pointing at the IAT at 0x2080.
>  # DISASM: 140001000:      8b 05 7a 10 00 00       movl    4218(%rip), %eax
>  # DISASM: 140001006:      c3      retq
> @@ -41,6 +42,10 @@
>  # CONTENTS:  140003000 80200040 01000000 00200040 01000000
>  # CONTENTS:  140003010 24200040 01000000
>
> +# Check that the automatically imported symbol "variable" is not listed in
> +# the symbol table.
> +# SYMBOLS-NOT: variable
> +
>      .global main
>      .text
>  main:
>
>
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