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Tue, 22 Jul 2025 08:56:55 GMT Received: from smtpav05.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 0EBDE20040; Tue, 22 Jul 2025 08:56:55 +0000 (GMT) Received: from smtpav05.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id D100720043; Tue, 22 Jul 2025 08:56:52 +0000 (GMT) Received: from localhost.localdomain (unknown [9.109.199.41]) by smtpav05.fra02v.mail.ibm.com (Postfix) with ESMTP; Tue, 22 Jul 2025 08:56:52 +0000 (GMT) From: Aditya Bodkhe To: 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, venkat88@linux.ibm.com, Aditya Bodkhe Subject: [PATCH v2 1/2] powerpc/ftrace: support CONFIG_FUNCTION_GRAPH_RETVAL Date: Tue, 22 Jul 2025 14:26:47 +0530 Message-ID: <20250722085648.1640-1-adityab1@linux.ibm.com> X-Mailer: git-send-email 2.50.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: U8dQhvN24Q4MFv_KRg1SnPiwVjLESJwb X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwNzIyMDA3MSBTYWx0ZWRfX1AN4ZemIuZa0 olXWi+IJZXqQDOFIhwbcIwzD4r9EJr45Ht64Xgo1W/idIvRSxCv3hDJffCKEYrwoqsT8SO/nq37 dgD802z6dy2fl0limv31NUBZCAqXYv6gwNt1HfiInJELS2f9Q+w51XaIroD/rhBGxUhoqQVq1XY 5q7Y0V6M/Mb7gKKCxqabn8RFsuAe5JiUzz9eo1fF+RnjKI7TnQtQGY2WoTm7uppja+T8bxIKNmw HutLlDvWOPRrdpr/eDSgKETxckkkSvIaLqZYixletRHoK1Ac+gTghjc0q5ZB6S8QqMb7ndUUnMU FxLGNwX8537jJgWIDCktCE77CEbhlOPx+Xl3ZwiWutMTuJYj+MgZqLAqspxxNg7KfxAlqlzBuTD HHQjoZ4ufLkZRVELcU2ndnOJnQ3qFF9O5M6O5HzEhSbqKrXN96BRCqM7Xerklgb3nqWngklc X-Authority-Analysis: v=2.4 cv=dpnbC0g4 c=1 sm=1 tr=0 ts=687f525c cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=Wb1JkmetP80A:10 a=VnNF1IyMAAAA:8 a=f-JPSP1mq3vSRxYuwIAA:9 X-Proofpoint-GUID: Zqytb6L4fNSzmhhgppjFwLE_bxEJ82nN X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1099,Hydra:6.1.9,FMLib:17.12.80.40 definitions=2025-07-22_01,2025-07-21_02,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 impostorscore=0 suspectscore=0 adultscore=0 phishscore=0 lowpriorityscore=0 priorityscore=1501 bulkscore=0 mlxscore=0 malwarescore=0 mlxlogscore=999 clxscore=1015 classifier=spam authscore=0 authtc=n/a authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2505280000 definitions=main-2507220071 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 --- 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 */ -- 2.50.0