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From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>, Yonghong Song <yhs@fb.com>,
	mingo@kernel.org, torvalds@linux-foundation.org, ast@fb.com,
	daniel@iogearbox.net, linux-kernel@vger.kernel.org,
	x86@kernel.org, netdev@vger.kernel.org, kernel-team@fb.com,
	Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH bpf v3] x86/cpufeature: bpf hack for clang not supporting asm goto
Date: Thu, 10 May 2018 10:58:35 -0700	[thread overview]
Message-ID: <20180510175833.nujqinu26mydeape@ast-mbp.dhcp.thefacebook.com> (raw)
In-Reply-To: <20180510162028.GB16130@pd.tnic>

On Thu, May 10, 2018 at 06:20:28PM +0200, Borislav Petkov wrote:
> On Thu, May 10, 2018 at 08:52:42AM -0700, Alexei Starovoitov wrote:
> > That makes me wonder what happened with "we do not break user space" rule?
> 
> As someone already pointed out on IRC, arch/x86/include/asm/cpufeature.h
> is solely a kernel header so nothing but kernel should include it. So
> forget the userspace breakage "argument".

libbcc is a library. It's not only used by bcc scripts, but by production
services that compile bpf programs with clang.
Without this kernel fix the companies won't be able to upgrade the kernel.
Even if we could somehow hack libbcc and workaround in user space
(which is not possible as already explained), it's a long dependency chain
to recompile and upgrade core services before upgrading the kernel
which makes even theoretical user space fix impractical.
I see no option, but to fix the kernel.
Regardless whether it's called user space breakage or kernel breakage.

  parent reply	other threads:[~2018-05-10 17:58 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-04  3:31 Yonghong Song
2018-05-10 10:06 ` Peter Zijlstra
2018-05-10 15:52   ` Alexei Starovoitov
2018-05-10 16:20     ` Borislav Petkov
2018-05-10 17:57       ` Gianluca Borello
2018-05-10 17:58       ` Alexei Starovoitov [this message]
2018-05-10 18:16         ` Borislav Petkov
2018-05-10 10:49 ` Borislav Petkov
2018-05-12 16:03 Alexei Starovoitov
2018-05-12 20:30 ` Thomas Gleixner
2018-05-13 17:43   ` Alexei Starovoitov
2018-05-13 18:02     ` Thomas Gleixner

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