Re: [PATCH 1/2] Makefile: Fix distcc compilation with x86 macros

[Nadav Amit <namit@vmware.com>]

From: Logan Gunthorpe
Sent: November 14, 2018 at 7:29:38 AM GMT
> To: Nadav Amit <namit@vmware.com>, Ingo Molnar <mingo@kernel.org>
> Cc: Ingo Molnar <mingo@redhat.com>, Masahiro Yamada <yamada.masahiro@socionext.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>, LKML <linux-kernel@vger.kernel.org>
> Subject: Re: [PATCH 1/2] Makefile: Fix distcc compilation with x86 macros
> 
> 
> 
> 
> On 13/11/18 11:34 AM, Nadav Amit wrote:
>> Just one question before I send v2, since I have second thoughts. Does it
>> make sense to require the “DISTCC” make parameter, or should it be set in
>> the Kconfig? It can be detected automatically, the same way gcc/clang are
>> detected or manually through a config option.
> 
> I very much prefer the make variable as it can be set in the environment
> without having to change the Kconfig.

Actually, we can just figure out whether distcc or icecc are used in the
Makefile according to the “version”, similarly to the way clang is detected.
This would neither require new Makefile arguments or Kconfig options.

What do you say about the following?

-- >8 --

Subject: [PATCH] Makefile: Fix distcc compilation with x86 macros

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>
---
 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..bac761c07bf8 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 is used, and when assembly macro files are needed, the compilation
+# stage and the assembly stage needs to be separated. Providing the "DISTCC=y"
+# option enables separate compilation and assembly.
+
+cmd_cc_o_c_direct = $(CC) $(c_flags) -c -o $(1) $<
+
+ifneq ($(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