Re: [PATCH v6 5/9] LoongArch/ftrace: Add DYNAMIC_FTRACE_WITH_REGS support

[Qing Zhang <zhangqing@loongson.cn>]

Hi, huacai
On 2022/11/15 下午5:24, Huacai Chen wrote:
> On Tue, Nov 15, 2022 at 5:22 PM Qing Zhang <zhangqing@loongson.cn> wrote:
>>
>> Hi, Huacai
>>
>> On 2022/11/15 下午4:41, Huacai Chen wrote:
>>> Hi, Qing,
>>>
>>> Patch5 and Patch6 are small and related, maybe they can be combined
>>> with a name "LoongArch/ftrace: Add DYNAMIC_FTRACE_WITH_{ARGS,REGS}
>>> support"
>> I think they should be independent due to different use scenarios.
>  From the commit message it seems  DYNAMIC_FTRACE_WITH_ARGS depend on
> DYNAMIC_FTRACE_WITH_REGS.

DYNAMIC_FTRACE_WITH_REGS : which allows trace function saved registers,
It means that these registers can be modified, eg: Kprobe、Livepatch.

DYNAMIC_FTRACE_WITH_ARGS: uses pt_regs as a parameter for get sp,
which means it can be used to access registers on the stack, and
use graph_ops::func to install return_hooker to replace the special
hook, eg: Livepatch.

 From the following Kconfig, they are reasonable as separate patches.
config LIVEPATCH
         bool "Kernel Live Patching"
         depends on DYNAMIC_FTRACE_WITH_REGS || DYNAMIC_FTRACE_WITH_ARGS

Thanks
- Qing
> 
> Huacai
>>
>> Thanks,
>> -Qing
>>>
>>> Huacai
>>>
>>> On Tue, Nov 15, 2022 at 10:55 AM Qing Zhang <zhangqing@loongson.cn> wrote:
>>>>
>>>> This patch implements DYNAMIC_FTRACE_WITH_REGS on LoongArch, which allows
>>>> a traced function's arguments (and some other registers) to be captured
>>>> into a struct pt_regs, allowing these to be inspected and modified.
>>>>
>>>> Co-developed-by: Jinyang He <hejinyang@loongson.cn>
>>>> Signed-off-by: Jinyang He <hejinyang@loongson.cn>
>>>> Signed-off-by: Qing Zhang <zhangqing@loongson.cn>
>>>> ---
>>>>    arch/loongarch/Kconfig              |  1 +
>>>>    arch/loongarch/include/asm/ftrace.h |  3 +++
>>>>    arch/loongarch/kernel/ftrace_dyn.c  | 17 ++++++++++++++
>>>>    arch/loongarch/kernel/mcount-dyn.S  | 36 +++++++++++++++++++++++++++--
>>>>    4 files changed, 55 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
>>>> index 615ce62422b8..12e3e91a68ae 100644
>>>> --- a/arch/loongarch/Kconfig
>>>> +++ b/arch/loongarch/Kconfig
>>>> @@ -90,6 +90,7 @@ config LOONGARCH
>>>>           select HAVE_DEBUG_STACKOVERFLOW
>>>>           select HAVE_DMA_CONTIGUOUS
>>>>           select HAVE_DYNAMIC_FTRACE
>>>> +       select HAVE_DYNAMIC_FTRACE_WITH_REGS
>>>>           select HAVE_EBPF_JIT
>>>>           select HAVE_EXIT_THREAD
>>>>           select HAVE_FAST_GUP
>>>> diff --git a/arch/loongarch/include/asm/ftrace.h b/arch/loongarch/include/asm/ftrace.h
>>>> index 76ca58767f4d..a3f974a7a5ce 100644
>>>> --- a/arch/loongarch/include/asm/ftrace.h
>>>> +++ b/arch/loongarch/include/asm/ftrace.h
>>>> @@ -28,6 +28,9 @@ struct dyn_ftrace;
>>>>    int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec);
>>>>    #define ftrace_init_nop ftrace_init_nop
>>>>
>>>> +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
>>>> +#define ARCH_SUPPORTS_FTRACE_OPS 1
>>>> +#endif
>>>>    #endif /* CONFIG_DYNAMIC_FTRACE */
>>>>    #endif /* __ASSEMBLY__ */
>>>>    #endif /* CONFIG_FUNCTION_TRACER */
>>>> diff --git a/arch/loongarch/kernel/ftrace_dyn.c b/arch/loongarch/kernel/ftrace_dyn.c
>>>> index 3fe791b6783e..ec3d951be50c 100644
>>>> --- a/arch/loongarch/kernel/ftrace_dyn.c
>>>> +++ b/arch/loongarch/kernel/ftrace_dyn.c
>>>> @@ -99,6 +99,23 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
>>>>           return ftrace_modify_code(pc, old, new, true);
>>>>    }
>>>>
>>>> +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
>>>> +int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
>>>> +                       unsigned long addr)
>>>> +{
>>>> +       unsigned long pc;
>>>> +       long offset;
>>>> +       u32 old, new;
>>>> +
>>>> +       pc = rec->ip + LOONGARCH_INSN_SIZE;
>>>> +
>>>> +       old = larch_insn_gen_bl(pc, old_addr);
>>>> +       new = larch_insn_gen_bl(pc, addr);
>>>> +
>>>> +       return ftrace_modify_code(pc, old, new, true);
>>>> +}
>>>> +#endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
>>>> +
>>>>    void arch_ftrace_update_code(int command)
>>>>    {
>>>>           command |= FTRACE_MAY_SLEEP;
>>>> diff --git a/arch/loongarch/kernel/mcount-dyn.S b/arch/loongarch/kernel/mcount-dyn.S
>>>> index 0c12cc108e6f..02835186b463 100644
>>>> --- a/arch/loongarch/kernel/mcount-dyn.S
>>>> +++ b/arch/loongarch/kernel/mcount-dyn.S
>>>> @@ -27,7 +27,7 @@
>>>>     * follows the LoongArch psABI well.
>>>>     */
>>>>
>>>> -       .macro  ftrace_regs_entry
>>>> +       .macro  ftrace_regs_entry allregs=0
>>>>           PTR_ADDI sp, sp, -PT_SIZE
>>>>           /* Save trace function ra at PT_ERA */
>>>>           PTR_S   ra, sp, PT_ERA
>>>> @@ -43,16 +43,48 @@
>>>>           PTR_S   a7, sp, PT_R11
>>>>           PTR_S   fp, sp, PT_R22
>>>>
>>>> +       .if \allregs
>>>> +       PTR_S   t0, sp, PT_R12
>>>> +       PTR_S   t1, sp, PT_R13
>>>> +       PTR_S   t2, sp, PT_R14
>>>> +       PTR_S   t3, sp, PT_R15
>>>> +       PTR_S   t4, sp, PT_R16
>>>> +       PTR_S   t5, sp, PT_R17
>>>> +       PTR_S   t6, sp, PT_R18
>>>> +       PTR_S   t7, sp, PT_R19
>>>> +       PTR_S   t8, sp, PT_R20
>>>> +       PTR_S   s0, sp, PT_R23
>>>> +       PTR_S   s1, sp, PT_R24
>>>> +       PTR_S   s2, sp, PT_R25
>>>> +       PTR_S   s3, sp, PT_R26
>>>> +       PTR_S   s4, sp, PT_R27
>>>> +       PTR_S   s5, sp, PT_R28
>>>> +       PTR_S   s6, sp, PT_R29
>>>> +       PTR_S   s7, sp, PT_R30
>>>> +       PTR_S   s8, sp, PT_R31
>>>> +       PTR_S   tp, sp, PT_R2
>>>> +       /* Clear it for later use as a flag sometimes. */
>>>> +       PTR_S   zero, sp, PT_R0
>>>> +       PTR_S   $r21, sp, PT_R21
>>>> +       .endif
>>>> +
>>>>           PTR_ADDI t8, sp, PT_SIZE
>>>>           PTR_S   t8, sp, PT_R3
>>>>
>>>>           .endm
>>>>
>>>>    SYM_CODE_START(ftrace_caller)
>>>> -       ftrace_regs_entry
>>>> +       ftrace_regs_entry allregs=0
>>>>           b       ftrace_common
>>>>    SYM_CODE_END(ftrace_caller)
>>>>
>>>> +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
>>>> +SYM_CODE_START(ftrace_regs_caller)
>>>> +       ftrace_regs_entry allregs=1
>>>> +       b       ftrace_common
>>>> +SYM_CODE_END(ftrace_regs_caller)
>>>> +#endif
>>>> +
>>>>    SYM_CODE_START(ftrace_common)
>>>>           PTR_ADDI        a0, ra, -8      /* arg0: ip */
>>>>           move            a1, t0          /* arg1: parent_ip */
>>>> --
>>>> 2.36.0
>>>>
>>>>
>>
>>