From: Nathan Chancellor <nathan@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>
Cc: tglx@linutronix.de, bp@alien8.de, dave.hansen@linux.intel.com,
x86@kernel.org, hpa@zytor.com, jpoimboe@kernel.org,
jbaron@akamai.com, rostedt@goodmis.org, ardb@kernel.org,
linux-kernel@vger.kernel.org, erhard_f@mailbox.org,
ndesaulniers@google.com, mhiramat@kernel.org,
sandipan.das@amd.com, llvm@lists.linux.dev
Subject: Re: [PATCH 0/3] static_call/x86: Handle clang's conditional tail calls
Date: Wed, 8 Feb 2023 15:36:49 -0700 [thread overview]
Message-ID: <Y+QkAXfhWfGevWz7@dev-arch.thelio-3990X> (raw)
In-Reply-To: <20230123205915.751729592@infradead.org>
Hi Peter and Ingo,
On Mon, Jan 23, 2023 at 09:59:15PM +0100, Peter Zijlstra wrote:
> Erhard reported boot fails on this AMD machine when using clang and bisected it
> to a commit introducing a few static_call()s. Turns out that when using clang
> with -Os it it very likely to generate conditional tail calls like:
>
> 0000000000000350 <amd_pmu_add_event>:
> 350: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1) 351: R_X86_64_NONE __fentry__-0x4
> 355: 48 83 bf 20 01 00 00 00 cmpq $0x0,0x120(%rdi)
> 35d: 0f 85 00 00 00 00 jne 363 <amd_pmu_add_event+0x13> 35f: R_X86_64_PLT32 __SCT__amd_pmu_branch_add-0x4
> 363: e9 00 00 00 00 jmp 368 <amd_pmu_add_event+0x18> 364: R_X86_64_PLT32 __x86_return_thunk-0x4
>
> And our inline static_call() patching code can't deal with those and BUG
> happens -- really early.
>
> These patches borrow the kprobe Jcc emulation to implement text_poke_bp() Jcc
> support, which is then used to teach inline static_call() about this form.
>
> ---
> arch/x86/include/asm/text-patching.h | 31 ++++++++++++++++++
> arch/x86/kernel/alternative.c | 62 +++++++++++++++++++++++++++---------
> arch/x86/kernel/kprobes/core.c | 38 +++++-----------------
> arch/x86/kernel/static_call.c | 50 +++++++++++++++++++++++++++--
> 4 files changed, 133 insertions(+), 48 deletions(-)
I noticed this series was applied to x86/alternatives versus
x86/urgent, even though this appears to be a regression since 6.1, as
Erhard hit this issue in that tree.
Additionally, a new change in LLVM main [1] causes conditional tail
calls to be emitted even at -O2, so this breakage will become more
noticeable over time. Is it possible to expedite this to mainline so
that it can be backported to 6.1? If not, no worries, but I figured I
would ask :)
I have a backport of this series to 6.1 prepared already [2], where it
appears to work for me but I will get wider testing before sending it
after this is in Linus' tree (regardless of when that is). I figured it
would not hurt to have other eyes on it ahead of time though.
[1]: https://github.com/llvm/llvm-project/commit/ee5585ed09aff2e54cb540fad4c33f0c93626b1b
[2]: https://git.kernel.org/nathan/l/cbl-1800-1774-6.1
Cheers,
Nathan
prev parent reply other threads:[~2023-02-08 22:36 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-23 20:59 [PATCH 0/3] static_call/x86: Handle clang's conditional tail calls Peter Zijlstra
2023-01-23 20:59 ` [PATCH 1/3] x86/alternative: Introduce int3_emulate_jcc() Peter Zijlstra
2023-01-31 14:22 ` [tip: x86/alternatives] x86/alternatives: " tip-bot2 for Peter Zijlstra
2023-01-23 20:59 ` [PATCH 2/3] x86/alternative: Teach text_poke_bp() to patch Jcc.d32 instructions Peter Zijlstra
2023-01-31 14:22 ` [tip: x86/alternatives] x86/alternatives: " tip-bot2 for Peter Zijlstra
2023-01-23 20:59 ` [PATCH 3/3] x86/static_call: Add support for Jcc tail-calls Peter Zijlstra
2023-01-23 22:44 ` Steven Rostedt
2023-01-24 13:06 ` Peter Zijlstra
2023-01-24 15:07 ` Steven Rostedt
2023-01-26 15:34 ` [PATCH v1.1 " Peter Zijlstra
2023-01-26 18:14 ` Nick Desaulniers
2023-02-06 16:07 ` Steven Rostedt
2023-01-31 14:22 ` [tip: x86/alternatives] " tip-bot2 for Peter Zijlstra
2023-02-08 22:36 ` Nathan Chancellor [this message]
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