Re: [PATCH v2 2/7] perf build: Add build support and capability for elfutils libasm

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [Medium] The LIBASM_DLOPEN build configuration is defined but completely lacks the corresponding C code to dynamically load the library.
- [Medium] Setting NO_LIBDW=1 fails to exclude libdw from the build, leading to unintended linkage and static build failures.
--

commit 2a3530a4ffc824890cb03d14fd777712b83cb02e
Author: Ian Rogers <irogers@google.com>

perf build: Add build support and capability for elfutils libasm

Configure perf build system to utilize the libasm feature check
(supporting both static and dynamic builds) and export the config flags.
Add "libasm" capability detection to perf check.

> diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
> index 6e7b15fab2ecc..8527d20f498f8 100644
> --- a/tools/perf/Makefile.config
> +++ b/tools/perf/Makefile.config

[ ... ]

> @@ -432,6 +439,7 @@ ifeq ($(feature-file-handle), 1)
>  endif
>  
>  ifdef NO_LIBELF
> +  NO_LIBASM := 1
>    NO_LIBDW := 1
>    NO_LIBUNWIND := 1
>    NO_LIBBPF := 1

[ ... ]

> @@ -1060,6 +1068,20 @@ ifndef NO_CAPSTONE
>    endif
>  endif
>  
> +ifndef NO_LIBASM
> +  $(call feature_check,libasm)
> +  ifeq ($(feature-libasm), 1)
> +    CFLAGS += -DHAVE_LIBASM_SUPPORT $(LIBASM_CFLAGS)
> +    ifdef LIBASM_DLOPEN
> +      CFLAGS += -DLIBASM_DLOPEN

[Severity: Medium]
Is there corresponding C code to handle the dlopen and dlsym wrappers for 
libasm?

It looks like if LIBASM_DLOPEN is defined, the build skips linking libasm 
directly. However, without the runtime dynamic loading implementation, won't 
this result in unresolved symbol linker errors when trying to build with 
LIBASM_DLOPEN=1?

> +    else
> +      LDFLAGS += $(LIBASM_LDFLAGS)
> +      EXTLIBS += -lasm -ldw -lelf

[Severity: Medium]
If a user configures the build with NO_LIBDW=1 to avoid linking libdw, won't
this unconditional addition of -ldw override their request?

Setting NO_LIBDW=1 does not implicitly set NO_LIBASM=1. As a result, the 
libasm feature check still executes and forcibly appends -ldw to EXTLIBS.

For static builds, will this cause linker errors since NO_LIBDW=1 skips adding
DWARFLIBS (like -lz and -lzstd) that libdw.a requires?

> +    endif
> +    $(call detected,CONFIG_LIBASM)
> +  endif
> +endif
> +

[ ... ]

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260609070732.545416-1-irogers@google.com?part=2