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Message-ID: <CAAhV-H4ok2r2FarFszwYJ6Hah4m7ieNf6egnXyZhUf1ESDUhXg@mail.gmail.com>
Date: Mon, 14 Nov 2022 14:50:28 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Jinyang He <hejinyang@...ngson.cn>
Cc: Tiezhu Yang <yangtiezhu@...ngson.cn>,
Masami Hiramatsu <mhiramat@...nel.org>,
loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/5] LoongArch: Add kretprobe support
On Mon, Nov 14, 2022 at 2:11 PM Jinyang He <hejinyang@...ngson.cn> wrote:
>
> On 2022/11/14 下午12:43, Huacai Chen wrote:
>
> > Hi, Tiezhu and Jinyang,
> >
> > On Wed, Sep 28, 2022 at 8:50 AM Tiezhu Yang <yangtiezhu@...ngson.cn> wrote:
> >> Use the generic kretprobe trampoline handler to add kretprobe
> >> support for LoongArch.
> >>
> >> Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
> >> ---
> >> arch/loongarch/Kconfig | 1 +
> >> arch/loongarch/kernel/Makefile | 2 +-
> >> arch/loongarch/kernel/kprobes.c | 24 ++++++++
> >> arch/loongarch/kernel/kprobes_trampoline.S | 97 ++++++++++++++++++++++++++++++
> >> 4 files changed, 123 insertions(+), 1 deletion(-)
> >> create mode 100644 arch/loongarch/kernel/kprobes_trampoline.S
> >>
> >> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> >> index 8debd70..877be6a 100644
> >> --- a/arch/loongarch/Kconfig
> >> +++ b/arch/loongarch/Kconfig
> >> @@ -95,6 +95,7 @@ config LOONGARCH
> >> select HAVE_IRQ_EXIT_ON_IRQ_STACK
> >> select HAVE_IRQ_TIME_ACCOUNTING
> >> select HAVE_KPROBES
> >> + select HAVE_KRETPROBES
> >> select HAVE_MOD_ARCH_SPECIFIC
> >> select HAVE_NMI
> >> select HAVE_PCI
> >> diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile
> >> index ff98d8a..48f50607 100644
> >> --- a/arch/loongarch/kernel/Makefile
> >> +++ b/arch/loongarch/kernel/Makefile
> >> @@ -33,6 +33,6 @@ obj-$(CONFIG_UNWINDER_PROLOGUE) += unwind_prologue.o
> >>
> >> obj-$(CONFIG_PERF_EVENTS) += perf_event.o perf_regs.o
> >>
> >> -obj-$(CONFIG_KPROBES) += kprobes.o
> >> +obj-$(CONFIG_KPROBES) += kprobes.o kprobes_trampoline.o
> >>
> >> CPPFLAGS_vmlinux.lds := $(KBUILD_CFLAGS)
> >> diff --git a/arch/loongarch/kernel/kprobes.c b/arch/loongarch/kernel/kprobes.c
> >> index c11f6e0..ca3f1dc 100644
> >> --- a/arch/loongarch/kernel/kprobes.c
> >> +++ b/arch/loongarch/kernel/kprobes.c
> >> @@ -306,6 +306,30 @@ int __init arch_populate_kprobe_blacklist(void)
> >> (unsigned long)__irqentry_text_end);
> >> }
> >>
> >> +/* Called from __kretprobe_trampoline */
> >> +void __used *trampoline_probe_handler(struct pt_regs *regs)
> >> +{
> >> + return (void *)kretprobe_trampoline_handler(regs, NULL);
> >> +}
> >> +NOKPROBE_SYMBOL(trampoline_probe_handler);
> >> +
> >> +void arch_prepare_kretprobe(struct kretprobe_instance *ri,
> >> + struct pt_regs *regs)
> >> +{
> >> + ri->ret_addr = (kprobe_opcode_t *)regs->regs[1];
> >> + ri->fp = NULL;
> >> +
> >> + /* Replace the return addr with trampoline addr */
> >> + regs->regs[1] = (unsigned long)&__kretprobe_trampoline;
> >> +}
> >> +NOKPROBE_SYMBOL(arch_prepare_kretprobe);
> >> +
> >> +int arch_trampoline_kprobe(struct kprobe *p)
> >> +{
> >> + return 0;
> >> +}
> >> +NOKPROBE_SYMBOL(arch_trampoline_kprobe);
> >> +
> >> int __init arch_init_kprobes(void)
> >> {
> >> return 0;
> >> diff --git a/arch/loongarch/kernel/kprobes_trampoline.S b/arch/loongarch/kernel/kprobes_trampoline.S
> >> new file mode 100644
> >> index 0000000..9888ab8
> >> --- /dev/null
> >> +++ b/arch/loongarch/kernel/kprobes_trampoline.S
> >> @@ -0,0 +1,97 @@
> >> +/* SPDX-License-Identifier: GPL-2.0+ */
> >> +#include <linux/linkage.h>
> >> +#include <asm/stackframe.h>
> >> +
> >> + .text
> >> +
> >> + .macro save_all_base_regs
> >> + cfi_st zero, PT_R0
> >> + cfi_st ra, PT_R1
> >> + cfi_st tp, PT_R2
> >> + cfi_st a0, PT_R4
> >> + cfi_st a1, PT_R5
> >> + cfi_st a2, PT_R6
> >> + cfi_st a3, PT_R7
> >> + cfi_st a4, PT_R8
> >> + cfi_st a5, PT_R9
> >> + cfi_st a6, PT_R10
> >> + cfi_st a7, PT_R11
> >> + cfi_st t0, PT_R12
> >> + cfi_st t1, PT_R13
> >> + cfi_st t2, PT_R14
> >> + cfi_st t3, PT_R15
> >> + cfi_st t4, PT_R16
> >> + cfi_st t5, PT_R17
> >> + cfi_st t6, PT_R18
> >> + cfi_st t7, PT_R19
> >> + cfi_st t8, PT_R20
> >> + cfi_st u0, PT_R21
> >> + cfi_st fp, PT_R22
> >> + cfi_st s0, PT_R23
> >> + cfi_st s1, PT_R24
> >> + cfi_st s2, PT_R25
> >> + cfi_st s3, PT_R26
> >> + cfi_st s4, PT_R27
> >> + cfi_st s5, PT_R28
> >> + cfi_st s6, PT_R29
> >> + cfi_st s7, PT_R30
> >> + cfi_st s8, PT_R31
> >> + addi.d t0, sp, PT_SIZE
> >> + LONG_S t0, sp, PT_R3
> >> + csrrd t0, LOONGARCH_CSR_CRMD
> >> + andi t0, t0, 0x7 /* extract bit[1:0] PLV, bit[2] IE */
> >> + LONG_S t0, sp, PT_PRMD
> >> + .endm
> >> +
> >> + .macro restore_all_base_regs
> >> + cfi_ld zero, PT_R0
> >> + cfi_ld tp, PT_R2
> >> + cfi_ld a0, PT_R4
> >> + cfi_ld a1, PT_R5
> >> + cfi_ld a2, PT_R6
> >> + cfi_ld a3, PT_R7
> >> + cfi_ld a4, PT_R8
> >> + cfi_ld a5, PT_R9
> >> + cfi_ld a6, PT_R10
> >> + cfi_ld a7, PT_R11
> >> + cfi_ld t0, PT_R12
> >> + cfi_ld t1, PT_R13
> >> + cfi_ld t2, PT_R14
> >> + cfi_ld t3, PT_R15
> >> + cfi_ld t4, PT_R16
> >> + cfi_ld t5, PT_R17
> >> + cfi_ld t6, PT_R18
> >> + cfi_ld t7, PT_R19
> >> + cfi_ld t8, PT_R20
> >> + cfi_ld u0, PT_R21
> >> + cfi_ld fp, PT_R22
> >> + cfi_ld s0, PT_R23
> >> + cfi_ld s1, PT_R24
> >> + cfi_ld s2, PT_R25
> >> + cfi_ld s3, PT_R26
> >> + cfi_ld s4, PT_R27
> >> + cfi_ld s5, PT_R28
> >> + cfi_ld s6, PT_R29
> >> + cfi_ld s7, PT_R30
> >> + cfi_ld s8, PT_R31
> >> + LONG_L t0, sp, PT_PRMD
> >> + li.d t1, 0x7 /* mask bit[1:0] PLV, bit[2] IE */
> >> + csrxchg t0, t1, LOONGARCH_CSR_CRMD
> >> + .endm
> > Do you think we need to save and restore all regs here?
> >
> > Huacai
>
> Hi, Huacai,
>
>
> Note that it is not function context. In the original kprobe design, it is
> triggered by 'break' and then trap into exception with all pt_regs saved.
> The all pt_regs will be visible to the user. So I think in this version
> we should also support all regs to user. BTW, due to all exceptions is
> trapped by 'break' something in pt_regs is not needed, like estat,
> badvaddr and so on.
OK, but I still have some questions:
1, Why $r0 need save/restore?
2, Why save $r1 but not restore?
3, What is the purpose of CRMD magic?
Huacai
>
>
> Thanks,
>
> Jinyang
>
> >> +
> >> +SYM_CODE_START(__kretprobe_trampoline)
> >> + addi.d sp, sp, -PT_SIZE
> >> + save_all_base_regs
> >> +
> >> + move a0, sp /* pt_regs */
> >> +
> >> + bl trampoline_probe_handler
> >> +
> >> + /* use the result as the return-address */
> >> + move ra, a0
> >> +
> >> + restore_all_base_regs
> >> + addi.d sp, sp, PT_SIZE
> >> +
> >> + jr ra
> >> +SYM_CODE_END(__kretprobe_trampoline)
> >> --
> >> 2.1.0
> >>
> >>
>
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