From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0D4DD30666 for ; Thu, 16 Nov 2023 17:24:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="HSrRtPnD" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DAD37C433CA; Thu, 16 Nov 2023 17:24:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1700155460; bh=/B6JGyRiiov2KpkuJVzSZzJhSDEp4Byf+qHwBNlACac=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=HSrRtPnDzSFpOZws4iU58xlCoKdKfHVEATrGDQoZ7zBqsZL7Es+u3steobl56VqfZ 8ELEuvzzClmT+SoR4pdB19wuF4Nn2HSOtq4C0uPT+Tx4AXcu5zzpPc8grHLpndzIZp djb0lFqTpdT6cn2K195abD6J9Al5uHiWDHoBTMpBbrqAw3+bZCuyfG3OAwBokreVk8 9hR7CYqoYNKQyGRsK1ecx40zKzTz0iIvKAFLYTfDSA5aXl0NcQ3YgSkFfyHh/xoB2f dx91geI8UZP+gi53v6IzL/AgKyeT/MwKp7SU9YnBswZfbgmqJ+1ZrHFeLkADPHNb2k GE/sk4hP9xHsg== Date: Thu, 16 Nov 2023 10:24:18 -0700 From: Nathan Chancellor To: Maria Yu Cc: linux@armlinux.org.uk, ardb@kernel.org, mhiramat@kernel.org, kernel@quicinc.com, linux-arm-kernel@lists.infradead.org, linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org, quic_lijuang@quicinc.com, stable@vger.kernel.org Subject: Re: [PATCH v2 1/1] ARM: kprobes: Explicitly reserve r7 for local variables Message-ID: <20231116172418.GA174808@dev-arch.thelio-3990X> References: <20231115095830.20607-1-quic_aiquny@quicinc.com> Precedence: bulk X-Mailing-List: linux-arm-msm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20231115095830.20607-1-quic_aiquny@quicinc.com> On Wed, Nov 15, 2023 at 05:58:30PM +0800, Maria Yu wrote: > Registers r7 is removed in clobber list, so compiler may choose r7 for > local variables usage, while r7 will be actually updated by the inline asm > code. This caused the runtime behavior wrong. > While those kind of reserved registers cannot be set to clobber list > because of error like "inline asm clobber list contains reserved > registers". > Explicitly reserve r7 by adding attribute no-omit-frame-pointer for needed > function, then in T32 asm code r7 is used as a frame pointer and is not > available for use as a general-purpose register. > Note that "no-omit-frame-pointer" will make the code size a little bigger > to store the stack frame pointer. So limited to needed functions can have > the less impact than the full source file. > > Fixes: dd12e97f3c72 ("ARM: kprobes: treat R7 as the frame pointer register in Thumb2 builds") > Signed-off-by: Maria Yu > Cc: stable@vger.kernel.org This causes warnings with clang: arch/arm/probes/kprobes/actions-thumb.c:441:47: warning: unknown attribute 'optimize' ignored [-Wunknown-attributes] 441 | static unsigned long __kprobes __attribute__((optimize("no-omit-frame-pointer"))) | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ arch/arm/probes/kprobes/actions-thumb.c:524:38: warning: unknown attribute 'optimize' ignored [-Wunknown-attributes] 524 | static void __kprobes __attribute__((optimize("no-omit-frame-pointer"))) | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ arch/arm/probes/kprobes/actions-thumb.c:560:38: warning: unknown attribute 'optimize' ignored [-Wunknown-attributes] 560 | static void __kprobes __attribute__((optimize("no-omit-frame-pointer"))) | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ arch/arm/probes/kprobes/actions-thumb.c:579:38: warning: unknown attribute 'optimize' ignored [-Wunknown-attributes] 579 | static void __kprobes __attribute__((optimize("no-omit-frame-pointer"))) | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 4 warnings generated. Furthermore, as far as I am aware, the optimize attribute has other issues so its use is discouraged, see commits 080b6f407635 ("bpf: Don't rely on GCC __attribute__((optimize)) to disable GCSE") and a7223f5bfcae ("powerpc: Avoid broken GCC __attribute__((optimize))"). Cheers, Nathan > --- > arch/arm/probes/kprobes/actions-thumb.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/arch/arm/probes/kprobes/actions-thumb.c b/arch/arm/probes/kprobes/actions-thumb.c > index 51624fc263fc..c2fdaf9f6dba 100644 > --- a/arch/arm/probes/kprobes/actions-thumb.c > +++ b/arch/arm/probes/kprobes/actions-thumb.c > @@ -438,7 +438,7 @@ t16_simulate_branch(probes_opcode_t insn, > regs->ARM_pc = pc + (offset * 2); > } > > -static unsigned long __kprobes > +static unsigned long __kprobes __attribute__((optimize("no-omit-frame-pointer"))) > t16_emulate_loregs(probes_opcode_t insn, > struct arch_probes_insn *asi, struct pt_regs *regs) > { > @@ -521,7 +521,7 @@ t16_decode_hiregs(probes_opcode_t insn, struct arch_probes_insn *asi, > return INSN_GOOD; > } > > -static void __kprobes > +static void __kprobes __attribute__((optimize("no-omit-frame-pointer"))) > t16_emulate_push(probes_opcode_t insn, > struct arch_probes_insn *asi, struct pt_regs *regs) > { > @@ -557,7 +557,7 @@ t16_decode_push(probes_opcode_t insn, struct arch_probes_insn *asi, > return INSN_GOOD; > } > > -static void __kprobes > +static void __kprobes __attribute__((optimize("no-omit-frame-pointer"))) > t16_emulate_pop_nopc(probes_opcode_t insn, > struct arch_probes_insn *asi, struct pt_regs *regs) > { > @@ -576,7 +576,7 @@ t16_emulate_pop_nopc(probes_opcode_t insn, > ); > } > > -static void __kprobes > +static void __kprobes __attribute__((optimize("no-omit-frame-pointer"))) > t16_emulate_pop_pc(probes_opcode_t insn, > struct arch_probes_insn *asi, struct pt_regs *regs) > { > > base-commit: 9bacdd8996c77c42ca004440be610692275ff9d0 > -- > 2.17.1 > > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel