linux-kernel - Re: [PATCH] Kbuild: Check for CONFIG_READABLE

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Message-ID: <20141005155816.GB9377@pd.tnic>
Date:	Sun, 5 Oct 2014 17:58:16 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	linux-kbuild@...r.kernel.org
Cc:	Michal Marek <mmarek@...e.cz>, LKML <linux-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>
Subject: Re: [PATCH] Kbuild: Check for CONFIG_READABLE_ASM when building .s
 targets

On Sun, Oct 05, 2014 at 05:32:34PM +0200, Borislav Petkov wrote:
> From: Borislav Petkov <bp@...e.de>
> 
> We do need to look at the asm output of c files for various reasons. In
> order to do so, we do make <path-to-filename>.s.
> 
> However, it can happen that the Kconfig option which enables the
> creation of readable asm CONFIG_READABLE_ASM is disabled. What is more,
> we want this option enabled because it indirectly enables the issue of
> line numbers in the asm done by gcc's switch -g.

Not really: so this is enabled by CONFIG_DEBUG_INFO and there are two
options: we make CONFIG_READABLE_ASM depend on it which makes people
answer a couple more questions or we simply add it to the command
building the .s file.

I say we do the second thing:

--
From: Borislav Petkov <bp@...e.de>
Subject: [PATCH -v1.1] Kbuild: Check for CONFIG_READABLE_ASM when building .s targets

We do need to look at the asm output of c files for various reasons. In
order to do so, we do make <path-to-filename>.s.

However, it can happen that the Kconfig option which enables the
creation of readable asm CONFIG_READABLE_ASM is disabled.

So issue a warning that the asm output might not be optimally readable
if that option is disabled.

Additionally, add the -g switch to the .s build command so that gcc
issues line numbers too.

Signed-off-by: Borislav Petkov <bp@...e.de>
---
 Makefile               | 2 +-
 scripts/Makefile.build | 7 ++++++-
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
index e43244263306..d9b505360c2a 100644
--- a/Makefile
+++ b/Makefile
@@ -1513,7 +1513,7 @@ else
 endif
 
 %.s: %.c prepare scripts FORCE
-	$(Q)$(MAKE) $(build)=$(build-dir) $(target-dir)$(notdir $@)
+	$(Q)$(MAKE) $(build)=$(build-dir) asm_target=$@ $(target-dir)$(notdir $@)
 %.i: %.c prepare scripts FORCE
 	$(Q)$(MAKE) $(build)=$(build-dir) $(target-dir)$(notdir $@)
 %.o: %.c prepare scripts FORCE
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index bf3e6778cd71..d55651d39638 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -147,7 +147,12 @@ $(multi-objs-y:.o=.s)   : modname = $(modname-multi)
 $(multi-objs-y:.o=.lst) : modname = $(modname-multi)
 
 quiet_cmd_cc_s_c = CC $(quiet_modtag)  $@
-cmd_cc_s_c       = $(CC) $(c_flags) $(DISABLE_LTO) -fverbose-asm -S -o $@ $<
+cmd_cc_s_c       = $(CC) $(c_flags) $(DISABLE_LTO) -fverbose-asm -g -S -o $@ $< \
+		   $(if $(findstring $(asm_target),$@),\
+			$(if $(__cmd_cc_s_c_once),,\
+				$(if $(CONFIG_READABLE_ASM),,\
+					$(warning Enable CONFIG_READABLE_ASM for more helpful asm); \
+					$(eval __cmd_cc_s_c_once=1)))) \
 
 $(obj)/%.s: $(src)/%.c FORCE
 	$(call if_changed_dep,cc_s_c)
-- 
2.0.0


-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
--
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