From: Peter Zijlstra <peterz@infradead.org>
To: Menglong Dong <menglong8.dong@gmail.com>
Cc: rostedt@goodmis.org, mark.rutland@arm.com,
alexei.starovoitov@gmail.com, catalin.marinas@arm.com,
will@kernel.org, mhiramat@kernel.org, tglx@linutronix.de,
mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com,
x86@kernel.org, hpa@zytor.com, mathieu.desnoyers@efficios.com,
nathan@kernel.org, ndesaulniers@google.com, morbo@google.com,
justinstitt@google.com, dongml2@chinatelecom.cn,
akpm@linux-foundation.org, rppt@kernel.org, graf@amazon.com,
dan.j.williams@intel.com, linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org,
bpf@vger.kernel.org, llvm@lists.linux.dev
Subject: Re: [PATCH bpf-next v2] add function metadata support
Date: Thu, 27 Feb 2025 17:53:02 +0100 [thread overview]
Message-ID: <20250227165302.GB5880@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <20250226121537.752241-1-dongml2@chinatelecom.cn>
On Wed, Feb 26, 2025 at 08:15:37PM +0800, Menglong Dong wrote:
> In x86, we need 5-bytes to prepend a "mov %eax xxx" insn, which can hold
> a 4-bytes index. So we have following logic:
>
> 1. use the head 5-bytes if CFI_CLANG is not enabled
> 2. use the tail 5-bytes if MITIGATION_CALL_DEPTH_TRACKING is not enabled
> 3. compile the kernel with extra 5-bytes padding if
> MITIGATION_CALL_DEPTH_TRACKING and CFI_CLANG are both enabled.
3) would result in 16+5 bytes padding, what does that do for alignment?
Functions should be 16 byte aligned.
Also, did you make sure all the code in arch/x86/kernel/alternative.c
still works? Because adding extra padding in the CFI_CLANG case moves
where the CFI bytes are emitted and all the CFI rewriting code goes
sideways.
next prev parent reply other threads:[~2025-02-27 16:53 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-02-26 12:15 [PATCH bpf-next v2] add function metadata support Menglong Dong
2025-02-27 15:18 ` kernel test robot
2025-02-27 16:32 ` kernel test robot
2025-02-27 16:53 ` Peter Zijlstra [this message]
2025-02-28 9:53 ` Menglong Dong
2025-02-28 10:26 ` Peter Zijlstra
2025-02-28 10:29 ` Peter Zijlstra
2025-02-28 13:01 ` Menglong Dong
2025-02-27 17:48 ` kernel test robot
2025-02-28 0:43 ` kernel test robot
2025-03-04 6:25 ` kernel test robot
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