linux-kernel - Re: [PATCH v2] purgatory: fix disabling debug info

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Message-ID: <CAKwvOdmTLCqLV8bfXY4X0xgg9eYaVNDEUwzbvNrK-SUTVhuxRQ@mail.gmail.com>
Date:   Mon, 27 Mar 2023 15:12:23 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Alyssa Ross <hi@...ssa.is>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Nick Cao <nickcao@...hi.co>, linux-kbuild@...r.kernel.org,
        Nathan Chancellor <nathan@...nel.org>,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        linux-riscv@...ts.infradead.org, Tom Rix <trix@...hat.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH v2] purgatory: fix disabling debug info

On Sun, Mar 26, 2023 at 11:23 AM Alyssa Ross <hi@...ssa.is> wrote:
>
> Since 32ef9e5054ec, -Wa,-gdwarf-2 is no longer used in KBUILD_AFLAGS.
> Instead, it includes -g, the appropriate -gdwarf-* flag, and also the
> -Wa versions of both of those if building with Clang and GNU as.  As a
> result, debug info was being generated for the purgatory objects, even
> though the intention was that it not be.

Ah, good catch!

>
> Fixes: 32ef9e5054ec ("Makefile.debug: re-enable debug info for .S files")
> Signed-off-by: Alyssa Ross <hi@...ssa.is>
> Cc: stable@...r.kernel.org
> ---
>
> Difference from v2: replace each AFLAGS_REMOVE_* assignment with a
> single aflags-remove-y line, and use foreach to add the -Wa versions,
> as suggested by Masahiro Yamada.
>
>  arch/riscv/purgatory/Makefile | 7 +------
>  arch/x86/purgatory/Makefile   | 3 +--
>  2 files changed, 2 insertions(+), 8 deletions(-)
>
> diff --git a/arch/riscv/purgatory/Makefile b/arch/riscv/purgatory/Makefile
> index d16bf715a586..5730797a6b40 100644
> --- a/arch/riscv/purgatory/Makefile
> +++ b/arch/riscv/purgatory/Makefile
> @@ -84,12 +84,7 @@ CFLAGS_string.o                      += $(PURGATORY_CFLAGS)
>  CFLAGS_REMOVE_ctype.o          += $(PURGATORY_CFLAGS_REMOVE)
>  CFLAGS_ctype.o                 += $(PURGATORY_CFLAGS)
>
> -AFLAGS_REMOVE_entry.o          += -Wa,-gdwarf-2
> -AFLAGS_REMOVE_memcpy.o         += -Wa,-gdwarf-2
> -AFLAGS_REMOVE_memset.o         += -Wa,-gdwarf-2
> -AFLAGS_REMOVE_strcmp.o         += -Wa,-gdwarf-2
> -AFLAGS_REMOVE_strlen.o         += -Wa,-gdwarf-2
> -AFLAGS_REMOVE_strncmp.o                += -Wa,-gdwarf-2

Removing the explicit `-Wa,-gdwarf-2` makes sense; nothing ever sets it.

> +asflags-remove-y               += $(foreach x, -g -gdwarf-4 -gdwarf-5, $(x) -Wa,$(x))

Is it simpler to just append `-g0` to the running list of asflags;
that should also disable the emission of debug info? Or does that not
remove debug info from the assembler?

Either way:
Acked-by: Nick Desaulniers <ndesaulniers@...gle.com>
and thanks for the patch!

>
>  $(obj)/purgatory.ro: $(PURGATORY_OBJS) FORCE
>                 $(call if_changed,ld)
> diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
> index 17f09dc26381..82fec66d46d2 100644
> --- a/arch/x86/purgatory/Makefile
> +++ b/arch/x86/purgatory/Makefile
> @@ -69,8 +69,7 @@ CFLAGS_sha256.o                       += $(PURGATORY_CFLAGS)
>  CFLAGS_REMOVE_string.o         += $(PURGATORY_CFLAGS_REMOVE)
>  CFLAGS_string.o                        += $(PURGATORY_CFLAGS)
>
> -AFLAGS_REMOVE_setup-x86_$(BITS).o      += -Wa,-gdwarf-2
> -AFLAGS_REMOVE_entry64.o                        += -Wa,-gdwarf-2
> +asflags-remove-y               += $(foreach x, -g -gdwarf-4 -gdwarf-5, $(x) -Wa,$(x))
>
>  $(obj)/purgatory.ro: $(PURGATORY_OBJS) FORCE
>                 $(call if_changed,ld)
>
> base-commit: da8e7da11e4ba758caf4c149cc8d8cd555aefe5f
> --
> 2.37.1
>


-- 
Thanks,
~Nick Desaulniers