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Date: Mon, 14 Nov 2022 14:11:13 +0800
From: Jinyang He <hejinyang@...ngson.cn>
To: Huacai Chen <chenhuacai@...nel.org>,
Tiezhu Yang <yangtiezhu@...ngson.cn>
Cc: 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 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.
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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