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

[Suren Baghdasaryan <surenb@google.com>]

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?

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.

>
> 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
>