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Tue, 9 Sep 2025 07:18:00 GMT Received: from smtpav07.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 4DD8E20040; Tue, 9 Sep 2025 07:18:00 +0000 (GMT) Received: from smtpav07.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 052B220043; Tue, 9 Sep 2025 07:17:57 +0000 (GMT) Received: from [9.43.21.165] (unknown [9.43.21.165]) by smtpav07.fra02v.mail.ibm.com (Postfix) with ESMTP; Tue, 9 Sep 2025 07:17:56 +0000 (GMT) Message-ID: Date: Tue, 9 Sep 2025 12:47:55 +0530 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 v3 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, christophe.leroy@csgroup.eu, rostedt@goodmis.org, mhiramat@kernel.org, mark.rutland@arm.com, Venkat Rao Bagalkote References: <20250909045615.50251-1-adityab1@linux.ibm.com> Content-Language: en-US From: Hari Bathini In-Reply-To: <20250909045615.50251-1-adityab1@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: vXfCZE_0cvAGRpCPEF7y3HQIaait3uaS X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwOTA2MDIzNSBTYWx0ZWRfX4H8nU5jqR/6X Q+/KacEVOef2pVLC93c4ikI3mQefj7T9YNDy+dbLppsDqyGv4dOE4/a9UTAL8P/quXQlpJlrNsJ w3IYK552YAmyX7P52Ry20HNG2OMJZydFsGVkHJ1k6kKMBcFU+xMIxvH8QmUWDfKZG6YdLEbbnyw pG3SB2MtVzLedl0gYRjxzxpbtqyi4HnuiZ3XnLSSndfIV3E8OA8QWxKlUJGj7RLcWGw8oUt6sWr ANDDtyI1YDyVd7ktxIL/AIOKyRmGjQqeCF8O0SWHdoE4gDtXqrjin54ZmxA//LBgcvPFQIBhe3c 8nO9Zbqz4kL59J3MM/+6qW/pWaTsoPASCQhICxSK8cHGm90uzyfYuVMu5ZHlCELfBe4z+8cMvAC lF2Dls9d X-Proofpoint-GUID: zXW5mYf8BmCY4BVrdt7wGSVf0siSEgGW X-Authority-Analysis: v=2.4 cv=F59XdrhN c=1 sm=1 tr=0 ts=68bfd4ae cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=IkcTkHD0fZMA:10 a=yJojWOMRYYMA:10 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=1UX6Do5GAAAA:8 a=dNnesIPfpvp5sUh9fRYA:9 a=QEXdDO2ut3YA:10 a=Et2XPkok5AAZYJIKzHr1:22 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1117,Hydra:6.1.9,FMLib:17.12.80.40 definitions=2025-09-08_06,2025-09-08_02,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 clxscore=1015 impostorscore=0 bulkscore=0 adultscore=0 spamscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2507300000 definitions=main-2509060235 On 09/09/25 10:26 am, Aditya Bodkhe wrote: > 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. > Looks good to me. Reviewed-by: Hari Bathini > Tested-by: Venkat Rao Bagalkote > Reviewed-by: Christophe Leroy > Signed-off-by: Aditya Bodkhe > --- > > Changelog: > v2 -> v3: > - Rebase on Linux 6.17-rc4 > > v2:https://lore.kernel.org/all/20250722085648.1640-1-adityab1@linux.ibm.com/ > > 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. > > v1:https://lore.kernel.org/all/20250528134820.74121-1-adityab1@linux.ibm.com/ > > --- > 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 93402a1d9c9f..451d0e140051 100644 > --- a/arch/powerpc/Kconfig > +++ b/arch/powerpc/Kconfig > @@ -246,6 +246,7 @@ 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..6599fe3c6234 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 */