Messages in this thread | | | From | Huacai Chen <> | Date | Mon, 14 Nov 2022 16:51:36 +0800 | Subject | Re: [PATCH v2 3/5] LoongArch: Add kretprobe support |
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On Mon, Nov 14, 2022 at 4:32 PM Jinyang He <hejinyang@loongson.cn> wrote: > > 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. ARM64 and RISC-V don't have such magics, so maybe they are unneeded?
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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