llvm dev - Feb 2021 - Some questions about lld with gdb-index option

I think the gdb-index support in lld only works with debug_gnu_pubnames in
the input files - so you would need to compile with -ggnu-pubnames.

Maybe lld could/should have a warning or something if the input files have
debug_* sections but don't have debug_gnu_pubnames when -Wl,--gdb-index is
specified.

On Sat, Feb 27, 2021 at 9:52 AM 何文婷 via llvm-dev <llvm-dev at
lists.llvm.org>
wrote:
> Hi all,
>     I am using below command to generate my object file named `myelf`:
>     `clang++-10 -Wl,--dynamic-linker,/lib64/ld-linux-x86-64.so.2
-fuse-ld=/.../usr/bin/ld.lld -rdynamic -Wl,—gdb-index -o myelf xxx.a xxx.a
xxx.a`
>     I found when link with -gdb-index option, it will generate the section
of .gdb_index in my elf file named myelf. But this gdb_index section is not
full, and when I gdb myelf to print some function like `abc` , it shows that no
symbol found(.gdb_index section donot have the function abc, but .debug_full and
.symtab has this function).
>     But When  I am using clang++ compile without gdb-index option  and then
using `gdb-add-index myelf `command to add gdb-index section, this section is
much larger, and When I gdb to print some function, all the symbols can be
found.
>     I do not understand, why lld generate a smaller .gdb_index section, and
is there any options to let me generate full .gdb_index section?
>
>     Waiting for some advices.
>
> Best wishes.
> hexiaoting
> 2020.2.25
>
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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It's very common for some input files to have gnu-pubnames, and some not.
So the warning would have to be somewhat smart.

On Sat, Feb 27, 2021 at 2:48 PM David Blaikie via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> I think the gdb-index support in lld only works with debug_gnu_pubnames in
> the input files - so you would need to compile with -ggnu-pubnames.
>
> Maybe lld could/should have a warning or something if the input files have
> debug_* sections but don't have debug_gnu_pubnames when -Wl,--gdb-index
is
> specified.
>
> On Sat, Feb 27, 2021 at 9:52 AM 何文婷 via llvm-dev <llvm-dev at
lists.llvm.org>
> wrote:
>
>> Hi all,
>>     I am using below command to generate my object file named `myelf`:
>>     `clang++-10 -Wl,--dynamic-linker,/lib64/ld-linux-x86-64.so.2
-fuse-ld=/.../usr/bin/ld.lld -rdynamic -Wl,—gdb-index -o myelf xxx.a xxx.a
xxx.a`
>>     I found when link with -gdb-index option, it will generate the
section of .gdb_index in my elf file named myelf. But this gdb_index section is
not full, and when I gdb myelf to print some function like `abc` , it shows that
no symbol found(.gdb_index section donot have the function abc, but .debug_full
and .symtab has this function).
>>     But When  I am using clang++ compile without gdb-index option  and
then  using `gdb-add-index myelf `command to add gdb-index section, this section
is much larger, and When I gdb to print some function, all the symbols can be
found.
>>     I do not understand, why lld generate a smaller .gdb_index section,
and is there any options to let me generate full .gdb_index section?
>>
>>     Waiting for some advices.
>>
>> Best wishes.
>> hexiaoting
>> 2020.2.25
>>
>>
>>
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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