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From:   Masahiro Yamada <yamada.masahiro@socionext.com>
Date:   Fri, 16 Nov 2018 16:45:45 +0900
Message-ID: <CAK7LNAREF_Pcejq1LJ=3K7h0M4o4oSRLfbeJc73O+8HV420Ziw@mail.gmail.com>
Subject: Re: [PATCH v2 1/2] Makefile: Fix distcc compilation with x86 macros
To:     Nadav Amit <namit@vmware.com>
Cc:     Ingo Molnar <mingo@redhat.com>,
        Michal Marek <michal.lkml@markovi.net>,
        Thomas Gleixner <tglx@linutronix.de>,
        Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>, X86 ML <x86@kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Thu, Nov 15, 2018 at 1:01 PM Nadav Amit <namit@vmware.com> wrote:
>
> Introducing the use of asm macros in c-code broke distcc, since it only
> sends the preprocessed source file. The solution is to break the
> compilation into two separate phases of compilation and assembly, and
> between the two concatenate the assembly macros and the compiled (yet
> not assembled) source file. Since this is less efficient, this
> compilation mode is only used when distcc or icecc are used.
>
> Note that the assembly stage should also be distributed, if distcc is
> configured using "CFLAGS=-DENABLE_REMOTE_ASSEMBLE".
>
> Reported-by: Logan Gunthorpe <logang@deltatee.com>
> Signed-off-by: Nadav Amit <namit@vmware.com>


Wow, this is so ugly.
I realized how much I hated this by now.

My question is, how long do we need to carry this?


As far as I understood from the long discussion
https://lkml.org/lkml/2018/10/7/92
people are trying to deal with it on the compiler side.
Is it right?


https://gcc.gnu.org/ml/gcc-patches/2018-10/msg01932.html

Once it is supported, what would happen on the kernel side?


> ---
>  Makefile               |  4 +++-
>  arch/x86/Makefile      |  7 +++++--
>  scripts/Makefile.build | 30 ++++++++++++++++++++++++++++--
>  3 files changed, 36 insertions(+), 5 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index 9fce8b91c15f..c07349fc38c7 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -743,7 +743,9 @@ KBUILD_CFLAGS   += $(call cc-option, -gsplit-dwarf, -g)
>  else
>  KBUILD_CFLAGS  += -g
>  endif
> -KBUILD_AFLAGS  += -Wa,-gdwarf-2
> +AFLAGS_DEBUG_INFO = -Wa,-gdwarf-2
> +export AFLAGS_DEBUG_INFO
> +KBUILD_AFLAGS  += $(AFLAGS_DEBUG_INFO)
>  endif
>  ifdef CONFIG_DEBUG_INFO_DWARF4
>  KBUILD_CFLAGS  += $(call cc-option, -gdwarf-4,)
> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> index f5d7f4134524..b5953cbcc9c8 100644
> --- a/arch/x86/Makefile
> +++ b/arch/x86/Makefile
> @@ -235,10 +235,13 @@ archscripts: scripts_basic
>  archheaders:
>         $(Q)$(MAKE) $(build)=arch/x86/entry/syscalls all
>
> +ASM_MACRO_FILE = arch/x86/kernel/macros.s
> +export ASM_MACRO_FILE
> +
>  archmacros:
> -       $(Q)$(MAKE) $(build)=arch/x86/kernel arch/x86/kernel/macros.s
> +       $(Q)$(MAKE) $(build)=arch/x86/kernel $(ASM_MACRO_FILE)
>
> -ASM_MACRO_FLAGS = -Wa,arch/x86/kernel/macros.s
> +ASM_MACRO_FLAGS = -Wa,$(ASM_MACRO_FILE)
>  export ASM_MACRO_FLAGS
>  KBUILD_CFLAGS += $(ASM_MACRO_FLAGS)
>
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index 6a6be9f440cf..b8d26bdf48b0 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -155,8 +155,34 @@ $(obj)/%.ll: $(src)/%.c FORCE
>
>  quiet_cmd_cc_o_c = CC $(quiet_modtag)  $@
>
> +# If distcc (or icecc) are used, and when assembly macro files are needed, the
> +# compilation stage and the assembly stage needs to be separated. Providing the
> +# "IGNORE_DISTCC=y" option disables separate compilation and assembly.
> +
> +cmd_cc_o_c_direct = $(CC) $(c_flags) -c -o $(1) $<
> +
> +ifneq ($(if $(IGNORE_DISTCC),,$(shell $(CC) --version 2>&1 | head -n 1 | grep -E 'distcc|ICECC')),)
> +a_flags_no_debug = $(filter-out $(AFLAGS_DEBUG_INFO), $(a_flags))
> +c_flags_no_macros = $(filter-out $(ASM_MACRO_FLAGS), $(c_flags))
> +
> +cmd_cc_o_c_two_steps =                                                 \
> +       $(CC) $(c_flags_no_macros) $(DISABLE_LTO) -fverbose-asm -S      \
> +               -o $(@D)/.$(@F:.o=.s) $<;                               \
> +       cat $(ASM_MACRO_FILE) $(@D)/.$(@F:.o=.s) >                      \
> +               $(@D)/.tmp_$(@F:.o=.s);                                 \
> +       $(CC) $(a_flags_no_debug) -c -o $(1) $(@D)/.tmp_$(@F:.o=.s);    \
> +       rm -f $(@D)/.$(@F:.o=.s) $(@D)/.tmp_$(@F:.o=.s)                 \
> +
> +cmd_cc_o_c_helper =                                                    \
> +       $(if $(findstring $(ASM_MACRO_FLAGS),$(c_flags)),               \
> +               $(call cmd_cc_o_c_two_steps, $(1)),                     \
> +               $(call cmd_cc_o_c_direct, $(1)))
> +else
> +cmd_cc_o_c_helper = $(call cmd_cc_o_c_direct, $(1))
> +endif
> +
>  ifndef CONFIG_MODVERSIONS
> -cmd_cc_o_c = $(CC) $(c_flags) -c -o $@ $<
> +cmd_cc_o_c = $(call cmd_cc_o_c_helper,$@)
>
>  else
>  # When module versioning is enabled the following steps are executed:
> @@ -171,7 +197,7 @@ else
>  #   replace the unresolved symbols __crc_exported_symbol with
>  #   the actual value of the checksum generated by genksyms
>
> -cmd_cc_o_c = $(CC) $(c_flags) -c -o $(@D)/.tmp_$(@F) $<
> +cmd_cc_o_c = $(call cmd_cc_o_c_helper,$(@D)/.tmp_$(@F))
>
>  cmd_modversions_c =                                                            \
>         if $(OBJDUMP) -h $(@D)/.tmp_$(@F) | grep -q __ksymtab; then             \
> --
> 2.17.1
>


-- 
Best Regards
Masahiro Yamada