Messages in this thread | | | Subject | Re: [PATCH v2 3/5] LoongArch: Add kretprobe support | From | Jinyang He <> | Date | Mon, 14 Nov 2022 16:32:40 +0800 |
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On 2022/11/14 下午2:50, Huacai Chen wrote:
> On Mon, Nov 14, 2022 at 2:11 PM Jinyang He <hejinyang@loongson.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@loongson.cn> wrote: >>>> 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/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?
Surely $r0 can be not saved, as now we do not have strange purpose to make PT_R0 as a flag.
> 2, Why save $r1 but not restore? My wrong idea is $r1 should be saved at CSR_ERA, to plays it like exception happened. But its value always equal the address of __kretprobe_trampoline. The kretprobe is something like fgraph. The real return address is returned by trampoline_probe_handler. And at present, the real return address is replaced in pt_regs->csr_era in __kretprobe_trampoline_handler(). So the $r1 saved in CSR_ERA will be destroied at __kretprobe_trampoline_handler() actually. That's why $r1 saved also is not needed.
And both way to get return address from return value or get return address
from pt_regs is same on LoongArch because arch_kretprobe_fixup_return()
does nothing. But I think get return address from pt_regs is more reliable.
> 3, What is the purpose of CRMD magic?
PT_CRMD magic is just exception context. It gives us a chance e.g. set ie off at func head, and ie on at func return.
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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