linux-kernel - Re: [RFC] perf build: Allow passing extra Clang flags via EXTRA_CLANG

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Message-ID: <aPRNSgunb8K9boWx@google.com>
Date: Sun, 19 Oct 2025 11:30:34 +0900
From: Namhyung Kim <namhyung@...nel.org>
To: hupu <hupu.gm@...il.com>
Cc: Leo Yan <leo.yan@....com>, Ian Rogers <irogers@...gle.com>,
	peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
	mark.rutland@....com, alexander.shishkin@...ux.intel.com,
	jolsa@...nel.org, adrian.hunter@...el.com, nathan@...nel.org,
	nick.desaulniers+lkml@...il.com, morbo@...gle.com,
	justinstitt@...gle.com, linux-kernel@...r.kernel.org,
	linux-perf-users@...r.kernel.org
Subject: Re: [RFC] perf build: Allow passing extra Clang flags via
 EXTRA_CLANG_FLAGS

Hello,

On Sat, Oct 18, 2025 at 06:05:03PM +0800, hupu wrote:
> Hi Leo, Ian, and fellow maintainers.
> 
> On Wed, Oct 15, 2025 at 7:47 PM hupu <hupu.gm@...il.com> wrote:
> >
> > Hi Leo,
> > Thank you for your reply.
> >
> > On Wed, Oct 15, 2025 at 5:30 PM Leo Yan <leo.yan@....com> wrote:
> > >
> > > Have you installed the GCC cross packages ?
> > >
> > >  $ sudo apt-get install gcc-aarch64-linux-gnu g++-aarch64-linux-gnu
> > >  $ sudo apt-get install libc6-dev-aarch64-cross linux-libc-dev-aarch64-cross
> > >  $ sudo apt-get install libc6-dev-arm64-cross linux-libc-dev-arm64-cross
> > >
> > > My understanding is arm64 cross compilation tries to find headers in the
> > > path /usr/aarch64-linux-gnu/include/ (I confirmed this on Ubuntu/Debian
> > > distros).  After install GCC cross packages, the headers should appear
> > > in the folder.
> > >
> >
> > I hadn’t installed the packages you mentioned earlier, but after
> > running the installation commands you provided, I was indeed able to
> > successfully build perf.
> >
> > In fact, I’m currently working on creating an SDK package, which
> > includes a cross-toolchain that I built myself using crosstool-NG. My
> > initial idea was to install certain third-party libraries (such as the
> > packages you mentioned) into the cross-toolchain’s sysroot directory.
> > With this approach, even when developing on different host machines,
> > we could simply specify the header search path (pointing to the
> > cross-toolchain’s sysroot directory) during compilation, and the build
> > should succeed without requiring any additional package installation
> > on the system.
> >
> > Based on this, I think allowing users to extend some options via
> > EXTRA_CLANG_FLAGS could be a flexible way to handle such cases.
> > However, this is just my personal thought and might not be entirely
> > correct, so I’d like to hear your advice.
> >
> 
> 
> Although installing the GCC cross packages allows me to build perf
> successfully, I still prefer to be able to pass additional Clang flags
> via EXTRA_CLANG_FLAGS, as this approach feels more flexible to me.
> 
> I look forward to continuing the discussion on this topic.

Doesn't EXTRA_CFLAGS work for you?

Thanks,
Namhyung