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 DB509137C20; Thu, 13 Jun 2024 19:09:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1718305764; cv=none; b=DWYbhgdpZS/HCD7O8CddL//tSVedSGYcROmijJ/R/uP7PmNNPR6cQUVT3g5TvdT5soTPM41UsD+bzza0MVOx39Zppmlz3ab++gRldO5pBMZA6FQ22E2IeMovZw0ukGtdOryCk5bAgH2lOEB9zwxlyFWgKhA+WDN/2SPYmzsV7x8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1718305764; c=relaxed/simple; bh=HFWyWh6KpryPRqXeZqS8bpwy4cpqT7565JH13UCYe8Q=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=URFTR3E1b82UiJldQXEDSVB+81XT14dvazmUnQ1xmmWrPkqxJ60oAQQPTip+jCV0NBpHp9mABL8MVyAZTINsOAaRb3IFKvGZgU9l67xF22UpQckhVG0beTo9YiduTZZ1cNngRDusphIOUkyTc+s2YcFxHggYNIASFngZtR4na0E= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=r15KrCdS; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="r15KrCdS" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5C484C2BBFC; Thu, 13 Jun 2024 19:09:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1718305763; bh=HFWyWh6KpryPRqXeZqS8bpwy4cpqT7565JH13UCYe8Q=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=r15KrCdS9IdIHad1rdEnJ2d8ckWytMU6LKbZHtECfabZeOOL5NeBLIxxPBq3z0zys 3slzhtA9cdHuWZnGZHDV5NLs2bTHbBZynuD7Q8DQOxVA09rVcITHteKZ+9+HgLXR5M HdoVCKVKrpzgEk2cSlL6jYQ71DUrUvpCH8y/LyXJsqZGTYjaU0YmUIsxGTKPGUwrAM uV1gBh1sR/ghA14TJc9M7AyHJIwf42TPHHmnNcaLCqawQObi8CV5wvWxi8CbRIG6cM TBm0dJY8W1NUsdLFkBf/mQlzHFacpAS20ZjS1cela3jB5ird9bozLTcvGNoQEx+Z3j J9N0ANl5gHr0g== Date: Thu, 13 Jun 2024 12:09:20 -0700 From: Nathan Chancellor To: Andy Chiu Cc: Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Zong Li , Steven Rostedt , Masami Hiramatsu , Mark Rutland , Nick Desaulniers , Bill Wendling , Justin Stitt , Puranjay Mohan , Palmer Dabbelt , linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, llvm@lists.linux.dev, Evgenii Shatokhin Subject: Re: [PATCH 4/8] riscv: ftrace: align patchable functions to 4 Byte boundary Message-ID: <20240613190920.GB1272931@thelio-3990X> References: <20240613-dev-andyc-dyn-ftrace-v4-v1-0-1a538e12c01e@sifive.com> <20240613-dev-andyc-dyn-ftrace-v4-v1-4-1a538e12c01e@sifive.com> Precedence: bulk X-Mailing-List: linux-trace-kernel@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: <20240613-dev-andyc-dyn-ftrace-v4-v1-4-1a538e12c01e@sifive.com> Hi Andy, On Thu, Jun 13, 2024 at 03:11:09PM +0800, Andy Chiu wrote: > We are changing ftrace code patching in order to remove dependency from > stop_machine() and enable kernel preemption. This requires us to align > functions entry at a 4-B align address. > > However, -falign-functions on older versions of GCC alone was not strong > enoungh to align all functions. In fact, cold functions are not aligned > after turning on optimizations. We consider this is a bug in GCC and > turn off guess-branch-probility as a workaround to align all functions. > > GCC bug id: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88345 > > The option -fmin-function-alignment is able to align all functions > properly on newer versions of gcc. So, we add a cc-option to test if > the toolchain supports it. > > Suggested-by: Evgenii Shatokhin > Signed-off-by: Andy Chiu > --- > arch/riscv/Kconfig | 1 + > arch/riscv/Makefile | 7 ++++++- > 2 files changed, 7 insertions(+), 1 deletion(-) > > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig > index b94176e25be1..80b8d48e1e46 100644 > --- a/arch/riscv/Kconfig > +++ b/arch/riscv/Kconfig > @@ -203,6 +203,7 @@ config CLANG_SUPPORTS_DYNAMIC_FTRACE > config GCC_SUPPORTS_DYNAMIC_FTRACE > def_bool CC_IS_GCC > depends on $(cc-option,-fpatchable-function-entry=8) > + depends on $(cc-option,-fmin-function-alignment=4) || !RISCV_ISA_C Please use CC_HAS_MIN_FUNCTION_ALIGNMENT (from arch/Kconfig), which already checks for support for this option. > config HAVE_SHADOW_CALL_STACK > def_bool $(cc-option,-fsanitize=shadow-call-stack) > diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile > index 06de9d365088..74628ad8dcf8 100644 > --- a/arch/riscv/Makefile > +++ b/arch/riscv/Makefile > @@ -14,8 +14,13 @@ endif > ifeq ($(CONFIG_DYNAMIC_FTRACE),y) > LDFLAGS_vmlinux += --no-relax > KBUILD_CPPFLAGS += -DCC_USING_PATCHABLE_FUNCTION_ENTRY > +ifeq ($(CONFIG_CC_IS_CLANG),y) Same here, please invert this and use ifdef CONFIG_CC_HAS_MIN_FUNCTION_ALIGNMENT like the main Makefile does. > + cflags_ftrace_align := -falign-functions=4 > +else > + cflags_ftrace_align := -fmin-function-alignment=4 > +endif > ifeq ($(CONFIG_RISCV_ISA_C),y) > - CC_FLAGS_FTRACE := -fpatchable-function-entry=4 > + CC_FLAGS_FTRACE := -fpatchable-function-entry=4 $(cflags_ftrace_align) > else > CC_FLAGS_FTRACE := -fpatchable-function-entry=2 > endif > > -- > 2.43.0 > >