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From:   Huacai Chen <chenhuacai@kernel.org>
Date:   Mon, 14 Nov 2022 14:50:28 +0800
Message-ID: <CAAhV-H4ok2r2FarFszwYJ6Hah4m7ieNf6egnXyZhUf1ESDUhXg@mail.gmail.com>
Subject: Re: [PATCH v2 3/5] LoongArch: Add kretprobe support
To:     Jinyang He <hejinyang@loongson.cn>
Cc:     Tiezhu Yang <yangtiezhu@loongson.cn>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        loongarch@lists.linux.dev, linux-kernel@vger.kernel.org
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On Mon, Nov 14, 2022 at 2:11 PM Jinyang He <hejinyang@loongson.cn> wrote:
>
> On 2022/11/14 =E4=B8=8B=E5=8D=8812:43, Huacai Chen wrote:
>
> > Hi, Tiezhu and Jinyang,
> >
> > On Wed, Sep 28, 2022 at 8:50 AM Tiezhu Yang <yangtiezhu@loongson.cn> wr=
ote:
> >> Use the generic kretprobe trampoline handler to add kretprobe
> >> support for LoongArch.
> >>
> >> Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.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/Ma=
kefile
> >> index ff98d8a..48f50607 100644
> >> --- a/arch/loongarch/kernel/Makefile
> >> +++ b/arch/loongarch/kernel/Makefile
> >> @@ -33,6 +33,6 @@ obj-$(CONFIG_UNWINDER_PROLOGUE) +=3D unwind_prologue=
.o
> >>
> >>   obj-$(CONFIG_PERF_EVENTS)      +=3D perf_event.o perf_regs.o
> >>
> >> -obj-$(CONFIG_KPROBES)          +=3D kprobes.o
> >> +obj-$(CONFIG_KPROBES)          +=3D kprobes.o kprobes_trampoline.o
> >>
> >>   CPPFLAGS_vmlinux.lds           :=3D $(KBUILD_CFLAGS)
> >> diff --git a/arch/loongarch/kernel/kprobes.c b/arch/loongarch/kernel/k=
probes.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_te=
xt_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 =3D (kprobe_opcode_t *)regs->regs[1];
> >> +       ri->fp =3D NULL;
> >> +
> >> +       /* Replace the return addr with trampoline addr */
> >> +       regs->regs[1] =3D (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/loongar=
ch/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 i=
s
> 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
> >>
> >>
>