Re: [PATCH 1/1] alloc_tag: remove empty module tag section from linker script

[Casey Chen <cachen@purestorage.com>]

On Thu, Jun 5, 2025 at 1:07 PM Suren Baghdasaryan <surenb@google.com> wrote:
>
> On Thu, Jun 5, 2025 at 12:01 PM Casey Chen <cachen@purestorage.com> wrote:
> >
> > The empty MOD_CODETAG_SECTIONS() macro added an incomplete .data
> > section in module linker script, which caused symbol lookup tools
> > like gdb to misinterpret symbol addresses e.g., __ib_process_cq
> > incorrectly mapping to unrelated functions like below.
> >
> >   (gdb) disas __ib_process_cq
> >   Dump of assembler code for function trace_event_fields_cq_schedule:
> >
> > Removing the empty section restores proper symbol resolution and
> > layout, ensuring .data placement behaves as expected.
>
> Hmm. I'm not sure why an empty .data section would cause such an
> issue. Is that expected behavior?
>

I'm not sure that's why I am posting this to ask for ideas. It looks
like gdb failed to disassemble function.

> To clarify, codetags are designed to support different types of tags,
> not only allocation tags which we currently use. It so happens that
> allocation tags can be still used after module unload, therefore they
> are placed into MOD_SEPARATE_CODETAG_SECTIONS(). If some other tags
> are added in the future and their lifecycle is the same as modules
> (IOW after module unload they can be unloaded too), then they would be
> added into MOD_CODETAG_SECTIONS() but until then this section is
> empty.
>

Could we remove the empty data section with MOD_CODETAG_SECTIONS() for
now until we really need it ?
> >
> > Fixes: 22d407b164ff ("lib: add allocation tagging support for memory allocation profiling")
> > Signed-off-by: Casey Chen <cachen@purestorage.com>
> > Reviewed-by: Yuanyuan Zhong <yzhong@purestorage.com>
> > ---
> >  scripts/module.lds.S | 5 -----
> >  1 file changed, 5 deletions(-)
> >
> > diff --git a/scripts/module.lds.S b/scripts/module.lds.S
> > index 711c6e029936..c071ca4beedd 100644
> > --- a/scripts/module.lds.S
> > +++ b/scripts/module.lds.S
> > @@ -50,17 +50,12 @@ SECTIONS {
> >         .data : {
> >                 *(.data .data.[0-9a-zA-Z_]*)
> >                 *(.data..L*)
> > -               MOD_CODETAG_SECTIONS()
> >         }
> >
> >         .rodata : {
> >                 *(.rodata .rodata.[0-9a-zA-Z_]*)
> >                 *(.rodata..L*)
> >         }
> > -#else
> > -       .data : {
> > -               MOD_CODETAG_SECTIONS()
> > -       }
> >  #endif
> >         MOD_SEPARATE_CODETAG_SECTIONS()
> >  }
> > --
> > 2.34.1
> >