Date:   Thu, 9 Feb 2023 11:56:03 +0100
From:   Damian Tometzki <dtometzki@fedoraproject.org>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     x86@kernel.org, jpoimboe@redhat.com, linux@weissschuh.net,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 00/10] objtool: Honey, I shrunk the instruction
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Reply-To: Damian Tometzki <dtometzki@fedoraproject.org>
Mail-Followup-To: Peter Zijlstra <peterz@infradead.org>, x86@kernel.org,
        jpoimboe@redhat.com, linux@weissschuh.net,
        linux-kernel@vger.kernel.org
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On Thu, 09. Feb 11:22, Peter Zijlstra wrote:
> On Wed, Feb 08, 2023 at 09:22:02PM +0100, Damian Tometzki wrote:
> > On Wed, 08. Feb 18:17, Peter Zijlstra wrote:
> > > Hi,
> > > 
> > > Boris complained he could no longer build allyesconfig on his 32G desktop
> > > machine without having OOM terminate either objtool or chrome.
> > > 
> > > After talking about these patches on IRC, Nathan mentioned the linux-clang CI
> > > was also having trouble of recent, and these patches appear to make it happy
> > > again.
> > > 
> > > In total these patches shrink an allyesconfig run by about 6G:
> > > 
> > > pre:	5:58.22 real,   226.69 user,    131.22 sys,     26221520 mem
> > > post:	5:03.34 real,   210.75 user,    88.80 sys,      20241232 mem
> > > 
> > > Also at:
> > > 
> > >   https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git/log/?h=objtool/core
> > > 
> > Hello Peter,
> > 
> > with clang-17 the build failed: 
> > In file included from weak.c:10:
> > In file included from /home/damian/kernel/linux/tools/objtool/include/objtool/objtool.h:13:
> > /home/damian/kernel/linux/tools/objtool/include/objtool/elf.h:88:86: error: '_Static_assert' with no message is a C2x extension [-Werror,-Wc2x-extensions]
> > static_assert(offsetof(struct reloc, rela.r_offset) == offsetof(struct reloc, offset));
> 
> Oh urgh. Apparently the kernel wrapper went missing in this userspace
> project :-)
> 
> include/linux/build_bug.h:#define static_assert(expr, ...) __static_assert(expr, ##__VA_ARGS__, #expr)
> 
> Anyway, it's that last patch and I meant to do that in a slightly less
> horrid way :-)

Hello Peter,

here a shortipossible fix: 
Then the build with clang works. 

diff --git a/tools/objtool/Makefile b/tools/objtool/Makefile
index 83b100c1e7f6..b7c8b476db95 100644
--- a/tools/objtool/Makefile
+++ b/tools/objtool/Makefile
@@ -31,7 +31,7 @@ INCLUDES := -I$(srctree)/tools/include \
            -I$(LIBSUBCMD_OUTPUT)/include
 # Note, EXTRA_WARNINGS here was determined for CC and not HOSTCC, it
 # is passed here to match a legacy behavior.
-WARNINGS := $(EXTRA_WARNINGS) -Wno-switch-default -Wno-switch-enum -Wno-packed -Wno-nested-externs
+WARNINGS := $(EXTRA_WARNINGS) -Wno-switch-default -Wno-switch-enum -Wno-packed -Wno-nested-externs -Wno-c2x-extensions
 OBJTOOL_CFLAGS := -Werror $(WARNINGS) $(KBUILD_HOSTCFLAGS) -g $(INCLUDES) $(LIBELF_FLAGS)