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[94.175.9.129]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-49597186eb9sm2616918f8f.35.2026.11.07.23.58.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 07 Nov 2026 23:58:11 -0800 (PST) Date: Sun, 8 Nov 2026 07:58:10 +0000 From: Stafford Horne To: Sahil Siddiq Cc: jonas@southpole.se, stefan.kristiansson@saunalahti.fi, naveen@kernel.org, davem@davemloft.net, mhiramat@kernel.org, pjw@kernel.org, wangruikang@iscas.ac.cn, namcao@linutronix.de, kees@kernel.org, linux-openrisc@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 4/4] openrisc: Add Kretprobes Message-ID: References: <20260930202744.50489-1-sahilcdq0@gmail.com> <20261026201240.107462-5-sahilcdq0@gmail.com> X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261026201240.107462-5-sahilcdq0@gmail.com> On Tue, Oct 27, 2026 at 01:42:40AM +0530, Sahil Siddiq wrote: > Add Kretprobes support for OpenRISC. Kretprobes allow a probe to be > fired when a function returns. They are built on top of the generic > rethook framework and also require the KProbe mechanism introduced > in the previous commit. This work is primarily based on similar work > done for RISC-V. > > Kretprobes work by inserting a KProbe at a function's entry point. > When the function begins to execute, the KProbe is fired and its > pre-handler replaces the function's return address with that of the > rethook trampoline. The trampoline in turn calls the kretprobe handler. > Control is returned to the original caller following this. > > Signed-off-by: Sahil Siddiq > --- > Changes v2 -> v3: > - arch/openrisc/kernel/rethook_trampoline.S: > (save_all_base_regs): Save SR and SP registers > (restore_all_base_regs): Restore SR register > > Changes v1 -> v2: New commit > > arch/openrisc/Kconfig | 2 + > arch/openrisc/kernel/Makefile | 1 + > arch/openrisc/kernel/rethook.c | 32 +++++++ > arch/openrisc/kernel/rethook.h | 8 ++ > arch/openrisc/kernel/rethook_trampoline.S | 111 ++++++++++++++++++++++ > 5 files changed, 154 insertions(+) > create mode 100644 arch/openrisc/kernel/rethook.c > create mode 100644 arch/openrisc/kernel/rethook.h > create mode 100644 arch/openrisc/kernel/rethook_trampoline.S > > diff --git a/arch/openrisc/Kconfig b/arch/openrisc/Kconfig > index d240533b424b..82365eb8f574 100644 > --- a/arch/openrisc/Kconfig > +++ b/arch/openrisc/Kconfig > @@ -28,6 +28,8 @@ config OPENRISC > select HAVE_ARCH_JUMP_LABEL_RELATIVE > select HAVE_PCI > select HAVE_KPROBES > + select HAVE_KRETPROBES > + select HAVE_RETHOOK > select HAVE_UID16 > select HAVE_PAGE_SIZE_8KB > select HAVE_REGS_AND_STACK_ACCESS_API > diff --git a/arch/openrisc/kernel/Makefile b/arch/openrisc/kernel/Makefile > index 0c1cade09e0c..e36537cea319 100644 > --- a/arch/openrisc/kernel/Makefile > +++ b/arch/openrisc/kernel/Makefile > @@ -15,6 +15,7 @@ obj-$(CONFIG_STACKTRACE) += stacktrace.o > obj-$(CONFIG_MODULES) += module.o > obj-$(CONFIG_OF) += prom.o > obj-$(CONFIG_KPROBES) += kprobes.o > +obj-$(CONFIG_RETHOOK) += rethook.o rethook_trampoline.o > obj-$(CONFIG_OR_KPROBES_KUNIT) += tests/ > obj-y += patching.o > > diff --git a/arch/openrisc/kernel/rethook.c b/arch/openrisc/kernel/rethook.c > new file mode 100644 > index 000000000000..50ef6715d044 > --- /dev/null > +++ b/arch/openrisc/kernel/rethook.c > @@ -0,0 +1,32 @@ > +// SPDX-License-Identifier: GPL-2.0-or-later > +/* > + * Generic return hook for OpenRISC. Depends on KProbes. > + * > + * Linux architectural port borrowing liberally from similar works of > + * others. All original copyrights apply as per the original source > + * declaration. > + * > + * OpenRISC implementation: > + * Copyright (C) 2026 Sahil Siddiq > + */ > + > +#include > +#include > +#include "rethook.h" > + > +unsigned long arch_rethook_trampoline_callback(struct pt_regs *regs) > +{ > + return rethook_trampoline_handler(regs, regs->gpr2); > +} > +NOKPROBE_SYMBOL(arch_rethook_trampoline_callback) > + > +void arch_rethook_prepare(struct rethook_node *rhn, struct pt_regs *regs, bool mcount) > +{ > + /* Store original return address and frame pointer */ > + rhn->ret_addr = regs->gpr9; > + rhn->frame = regs->gpr2; > + > + /* Set return address to trampoline */ > + regs->gpr9 = (unsigned long)arch_rethook_trampoline; Though this will work, in the kernel code we prefer to regs->gpr[n] syntax for accessing gprs. So to be consistent could you use that? i.e. regs->gpr[9]; > +} > +NOKPROBE_SYMBOL(arch_rethook_prepare) > diff --git a/arch/openrisc/kernel/rethook.h b/arch/openrisc/kernel/rethook.h > new file mode 100644 > index 000000000000..332306a5c380 > --- /dev/null > +++ b/arch/openrisc/kernel/rethook.h > @@ -0,0 +1,8 @@ > +/* SPDX-License-Identifier: GPL-2.0-or-later */ > +#ifndef __OPENRISC_RETHOOK_H > +#define __OPENRISC_RETHOOK_H > + > +unsigned long arch_rethook_trampoline_callback(struct pt_regs *regs); > +void arch_rethook_prepare(struct rethook_node *rhn, struct pt_regs *regs, bool mcount); > + > +#endif > diff --git a/arch/openrisc/kernel/rethook_trampoline.S b/arch/openrisc/kernel/rethook_trampoline.S > new file mode 100644 > index 000000000000..5e8fd5a65222 > --- /dev/null > +++ b/arch/openrisc/kernel/rethook_trampoline.S > @@ -0,0 +1,111 @@ > +/* SPDX-License-Identifier: GPL-2.0-or-later */ > +/* > + * Author: Sahil Siddiq > + */ > + > +#include > + > +#include > +#include > +#include > + > + .text > + > + .macro save_all_base_regs > + l.sw PT_GPR2(r1),r2 > + l.sw PT_GPR3(r1),r3 > + l.sw PT_GPR4(r1),r4 > + l.sw PT_GPR5(r1),r5 > + l.sw PT_GPR6(r1),r6 > + l.sw PT_GPR7(r1),r7 > + l.sw PT_GPR8(r1),r8 > + l.sw PT_GPR9(r1),r9 > + l.sw PT_GPR10(r1),r10 > + l.sw PT_GPR11(r1),r11 > + l.sw PT_GPR12(r1),r12 > + l.sw PT_GPR13(r1),r13 > + l.sw PT_GPR14(r1),r14 > + l.sw PT_GPR15(r1),r15 > + l.sw PT_GPR16(r1),r16 > + l.sw PT_GPR17(r1),r17 > + l.sw PT_GPR18(r1),r18 > + l.sw PT_GPR19(r1),r19 > + l.sw PT_GPR20(r1),r20 > + l.sw PT_GPR21(r1),r21 > + l.sw PT_GPR22(r1),r22 > + l.sw PT_GPR23(r1),r23 > + l.sw PT_GPR24(r1),r24 > + l.sw PT_GPR25(r1),r25 > + l.sw PT_GPR26(r1),r26 > + l.sw PT_GPR27(r1),r27 > + l.sw PT_GPR28(r1),r28 > + l.sw PT_GPR29(r1),r29 > + l.sw PT_GPR30(r1),r30 > + l.sw PT_GPR31(r1),r31 > + /* Save SR in pt_regs */ > + l.mfspr r13,r0,SPR_SR > + l.sw PT_SR(r1),r13 > + /* Save SP in pt_regs as it was prior to setting up this frame */ > + l.addi r13,r1,PT_SIZE > + l.sw PT_SP(r1),r13 > + .endm > + > + .macro restore_all_base_regs > + /* Restore SR from pt_regs */ > + l.lwz r13,PT_SR(r1) > + l.mtspr r0,r13,SPR_SR > + /* > + * r1 doesn't need to be explicitly restored from pt_regs. When > + * arch_rethook_trampoline_callback finishes, it restores SP to > + * what it was before its frame was set up. > + */ > + l.lwz r2,PT_GPR2(r1) > + l.lwz r3,PT_GPR3(r1) > + l.lwz r4,PT_GPR4(r1) > + l.lwz r5,PT_GPR5(r1) > + l.lwz r6,PT_GPR6(r1) > + l.lwz r7,PT_GPR7(r1) > + l.lwz r8,PT_GPR8(r1) > + /* Return address in r9 is stale, so don't restore it */ > + l.lwz r10,PT_GPR10(r1) > + l.lwz r11,PT_GPR11(r1) > + l.lwz r12,PT_GPR12(r1) > + l.lwz r13,PT_GPR13(r1) > + l.lwz r14,PT_GPR14(r1) > + l.lwz r15,PT_GPR15(r1) > + l.lwz r16,PT_GPR16(r1) > + l.lwz r17,PT_GPR17(r1) > + l.lwz r18,PT_GPR18(r1) > + l.lwz r19,PT_GPR19(r1) > + l.lwz r20,PT_GPR20(r1) > + l.lwz r21,PT_GPR21(r1) > + l.lwz r22,PT_GPR22(r1) > + l.lwz r23,PT_GPR23(r1) > + l.lwz r24,PT_GPR24(r1) > + l.lwz r25,PT_GPR25(r1) > + l.lwz r26,PT_GPR26(r1) > + l.lwz r27,PT_GPR27(r1) > + l.lwz r28,PT_GPR28(r1) > + l.lwz r29,PT_GPR29(r1) > + l.lwz r30,PT_GPR30(r1) > + l.lwz r31,PT_GPR31(r1) > + .endm > + > +SYM_CODE_START(arch_rethook_trampoline) > + /* Allocate enough space on stack for pt_regs */ > + l.addi r1,r1,-PT_SIZE > + save_all_base_regs > + > + l.addi r3,r1,0 /* pt_regs */ > + l.jal arch_rethook_trampoline_callback > + l.nop Could you indent the delay slot? For example: l.jal ... l.nop > + > + /* use the result as the return-address */ > + l.addi r9,r11,0 > + > + restore_all_base_regs > + l.addi r1,r1,PT_SIZE > + > + l.jr r9 > + l.nop Indent here too. > +SYM_CODE_END(arch_rethook_trampoline) Thanks, -Stafford