From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from pegase1.c-s.fr (pegase1.c-s.fr [93.17.236.30]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 682A51F4612; Mon, 4 Aug 2025 14:50:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=93.17.236.30 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754319037; cv=none; b=tnv6SoaXRcLYASbCGlwpT9XRLh6XAhywwTllf3p9n5vtEdws7uHJBLSwrKUHWtQEUtRcgUzet6xjG3Q8gd2iRx1RYGcEsojmBmIG5U+Vicxs7uakJfp9ljLqpAZJS/rfFQIblpGAvldUjodZ7qqwzUDbmWkuTU/mZJgmIkYeDfk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754319037; c=relaxed/simple; bh=Lv0zUTekwP29mYEeNY8FP4NK5pv608kruRZBw117cek=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=mmnpBLWhqj1nMQoaUHvFxcq0QJzEirbGBh3bSkUSMcOtCOItle/YT9f3iGpCTEW7db07/BCsffnnMAI1PxQ/NmfbfoieGGzL483pCw7tmV7i8VLmmOqW10ZX4KnajsHz7licwqeV4cIhEHxaZtclEZQ7wCtrmz7WI0cweY9rCwY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=csgroup.eu; spf=pass smtp.mailfrom=csgroup.eu; arc=none smtp.client-ip=93.17.236.30 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=csgroup.eu Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=csgroup.eu Received: from localhost (mailhub3.si.c-s.fr [192.168.12.233]) by localhost (Postfix) with ESMTP id 4bwdx61Fwbz9t2k; Mon, 4 Aug 2025 16:19:54 +0200 (CEST) X-Virus-Scanned: amavisd-new at c-s.fr Received: from pegase1.c-s.fr ([192.168.12.234]) by localhost (pegase1.c-s.fr [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id aafYWNPsnuTc; Mon, 4 Aug 2025 16:19:54 +0200 (CEST) Received: from messagerie.si.c-s.fr (messagerie.si.c-s.fr [192.168.25.192]) by pegase1.c-s.fr (Postfix) with ESMTP id 4bwdx60NySz9t2V; Mon, 4 Aug 2025 16:19:54 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 0679F8B766; Mon, 4 Aug 2025 16:19:54 +0200 (CEST) X-Virus-Scanned: amavisd-new at c-s.fr Received: from messagerie.si.c-s.fr ([127.0.0.1]) by localhost (messagerie.si.c-s.fr [127.0.0.1]) (amavisd-new, port 10023) with ESMTP id 25xDQtsmUhRS; Mon, 4 Aug 2025 16:19:53 +0200 (CEST) Received: from [10.25.207.160] (unknown [10.25.207.160]) by messagerie.si.c-s.fr (Postfix) with ESMTP id BF56C8B763; Mon, 4 Aug 2025 16:19:53 +0200 (CEST) Message-ID: <7e1adda9-4348-4c4e-953e-3fd21e4ff3c5@csgroup.eu> Date: Mon, 4 Aug 2025 16:19:53 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/2] powerpc/ftrace: support CONFIG_FUNCTION_GRAPH_RETVAL To: Aditya Bodkhe , linuxppc-dev@lists.ozlabs.org Cc: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, maddy@linux.ibm.com, mpe@ellerman.id.au, npiggin@gmail.com, rostedt@goodmis.org, mhiramat@kernel.org, mark.rutland@arm.com, venkat88@linux.ibm.com References: <20250722085648.1640-1-adityab1@linux.ibm.com> From: Christophe Leroy Content-Language: fr-FR In-Reply-To: <20250722085648.1640-1-adityab1@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Le 22/07/2025 à 10:56, Aditya Bodkhe a écrit : > commit a1be9ccc57f0 ("function_graph: Support recording and printing the > return value of function") introduced support for function graph return > value tracing. > > Additionally, commit a3ed4157b7d8 ("fgraph: Replace fgraph_ret_regs with > ftrace_regs") further refactored and optimized the implementation, > making `struct fgraph_ret_regs` unnecessary. > > This patch enables the above modifications for powerpc all, ensuring that > function graph return value tracing is available on this architecture. > > In this patch we have redefined two functions: > - 'ftrace_regs_get_return_value()' - the existing implementation on > ppc returns -ve of return value based on some conditions not > relevant to our patch. > - 'ftrace_regs_get_frame_pointer()' - always returns 0 in current code . > > We also allocate stack space to equivalent of 'SWITCH_FRAME_SIZE', > allowing us to directly use predefined offsets like 'GPR3' and 'GPR4' > this keeps code clean and consistent with already defined offsets . > > After this patch, v6.14+ kernel can also be built with FPROBE on powerpc > but there are a few other build and runtime dependencies for FPROBE to > work properly. The next patch addresses them. > > Signed-off-by: Aditya Bodkhe Reviewed-by: Christophe Leroy > --- > > Changelog: > v1 -> v2: > - Added explanation for redefining ftrace_regs_get_return_value() > and ftrace_regs_get_frame_pointer() > - Explained why stack space equivalent to 'SWITCH_FRAME_SIZE' is allocated. > > arch/powerpc/Kconfig | 1 + > arch/powerpc/include/asm/ftrace.h | 15 +++++++++ > arch/powerpc/kernel/trace/ftrace_entry.S | 42 ++++++++++++++---------- > 3 files changed, 41 insertions(+), 17 deletions(-) > > diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig > index c3e0cc83f120..9163521bc4b9 100644 > --- a/arch/powerpc/Kconfig > +++ b/arch/powerpc/Kconfig > @@ -250,6 +250,7 @@ config PPC > select HAVE_FUNCTION_ARG_ACCESS_API > select HAVE_FUNCTION_DESCRIPTORS if PPC64_ELF_ABI_V1 > select HAVE_FUNCTION_ERROR_INJECTION > + select HAVE_FUNCTION_GRAPH_FREGS > select HAVE_FUNCTION_GRAPH_TRACER > select HAVE_FUNCTION_TRACER if !COMPILE_TEST && (PPC64 || (PPC32 && CC_IS_GCC)) > select HAVE_GCC_PLUGINS if GCC_VERSION >= 50200 # plugin support on gcc <= 5.1 is buggy on PPC > diff --git a/arch/powerpc/include/asm/ftrace.h b/arch/powerpc/include/asm/ftrace.h > index 82da7c7a1d12..6ffc9c9cf4e3 100644 > --- a/arch/powerpc/include/asm/ftrace.h > +++ b/arch/powerpc/include/asm/ftrace.h > @@ -50,6 +50,21 @@ static __always_inline struct pt_regs *arch_ftrace_get_regs(struct ftrace_regs * > asm volatile("mfmsr %0" : "=r" ((_regs)->msr)); \ > } while (0) > > +#undef ftrace_regs_get_return_value > +static __always_inline unsigned long > +ftrace_regs_get_return_value(const struct ftrace_regs *fregs) > +{ > + return arch_ftrace_regs(fregs)->regs.gpr[3]; > +} > +#define ftrace_regs_get_return_value ftrace_regs_get_return_value > + > +#undef ftrace_regs_get_frame_pointer > +static __always_inline unsigned long > +ftrace_regs_get_frame_pointer(const struct ftrace_regs *fregs) > +{ > + return arch_ftrace_regs(fregs)->regs.gpr[1]; > +} > + > static __always_inline void > ftrace_regs_set_instruction_pointer(struct ftrace_regs *fregs, > unsigned long ip) > diff --git a/arch/powerpc/kernel/trace/ftrace_entry.S b/arch/powerpc/kernel/trace/ftrace_entry.S > index 3565c67fc638..3da14d8271d9 100644 > --- a/arch/powerpc/kernel/trace/ftrace_entry.S > +++ b/arch/powerpc/kernel/trace/ftrace_entry.S > @@ -409,23 +409,31 @@ EXPORT_SYMBOL(_mcount) > _GLOBAL(return_to_handler) > /* need to save return values */ > #ifdef CONFIG_PPC64 > - std r4, -32(r1) > - std r3, -24(r1) > + stdu r1, -SWITCH_FRAME_SIZE(r1) > + std r4, GPR4(r1) > + std r3, GPR3(r1) > + /* Save previous stack pointer (r1) */ > + addi r3, r1, SWITCH_FRAME_SIZE > + std r3, GPR1(r1) > /* save TOC */ > - std r2, -16(r1) > - std r31, -8(r1) > + std r2, 24(r1) > + std r31, 32(r1) > mr r31, r1 > - stdu r1, -112(r1) > - > + /* pass ftrace_regs/pt_regs to ftrace_return_to_handler */ > + addi r3, r1, STACK_INT_FRAME_REGS > /* > * We might be called from a module. > * Switch to our TOC to run inside the core kernel. > */ > LOAD_PACA_TOC() > #else > - stwu r1, -16(r1) > - stw r3, 8(r1) > - stw r4, 12(r1) > + stwu r1, -SWITCH_FRAME_SIZE(r1) > + stw r4, GPR4(r1) > + stw r3, GPR3(r1) > + addi r3, r1, SWITCH_FRAME_SIZE > + stw r3, GPR1(r1) > + /* pass ftrace_regs/pt_regs to ftrace_return_to_handler */ > + addi r3, r1, STACK_INT_FRAME_REGS > #endif > > > bl ftrace_return_to_handler > @@ -435,15 +443,15 @@ _GLOBAL(return_to_handler) > mtlr r3 > > #ifdef CONFIG_PPC64 > - ld r1, 0(r1) > - ld r4, -32(r1) > - ld r3, -24(r1) > - ld r2, -16(r1) > - ld r31, -8(r1) > + ld r4, GPR4(r1) > + ld r3, GPR3(r1) > + ld r2, 24(r1) > + ld r31, 32(r1) > + ld r1, 0(r1) > #else > - lwz r3, 8(r1) > - lwz r4, 12(r1) > - addi r1, r1, 16 > + lwz r3, GPR3(r1) > + lwz r4, GPR4(r1) > + addi r1, r1, SWITCH_FRAME_SIZE > #endif > > /* Jump back to real return address */