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

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Message-ID: <CADHxFxS3kDeSM7NvZHbdoOyqxzzcKeAc1xzr=q_f+T96G9preA@mail.gmail.com>
Date: Sat, 18 Oct 2025 18:05:03 +0800
From: hupu <hupu.gm@...il.com>
To: Leo Yan <leo.yan@....com>, Ian Rogers <irogers@...gle.com>
Cc: namhyung@...nel.org, 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

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.

Thanks,
hupu