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 <a6ce4a5e-bec7-bb0e-9765-c2d39f2f4e64@yadro.com>
In-Reply-To: <a6ce4a5e-bec7-bb0e-9765-c2d39f2f4e64@yadro.com>
From:   Guo Ren <guoren@kernel.org>
Date:   Wed, 11 Jan 2023 16:23:26 +0800
Message-ID: <CAJF2gTSTx_ZymEQdO_5dNmB-C2GgT1CN2mYoKLa-KsFw4AFzAw@mail.gmail.com>
Subject: Re: [PATCH -next V6 5/7] riscv: ftrace: Make ftrace_caller call ftrace_graph_func
To:     Evgenii Shatokhin <e.shatokhin@yadro.com>
Cc:     linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
        anup@brainfault.org, paul.walmsley@sifive.com, palmer@dabbelt.com,
        conor.dooley@microchip.com, heiko@sntech.de, rostedt@goodmis.org,
        mhiramat@kernel.org, jolsa@redhat.com, bp@suse.de,
        jpoimboe@kernel.org, suagrfillet@gmail.com, andy.chiu@sifive.com,
        linux@yadro.com
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On Wed, Jan 11, 2023 at 1:16 AM Evgenii Shatokhin <e.shatokhin@yadro.com> wrote:
>
> On 07.01.2023 16:35, guoren@kernel.org wrote:
> > From: Song Shuai <suagrfillet@gmail.com>
> >
> > In order to make the function graph use ftrace directly, ftrace_caller
> > should be adjusted to save the necessary regs against the pt_regs layout
> > so it can call ftrace_graph_func reasonably.
> >
> > SAVE_ALL now saves all the regs according to the pt_regs struct. Here
> > supersedes SAVE_ALL by SAVE_ABI_REGS which has an extra option to allow
> > saving only the necessary ABI-related regs for ftrace_caller.
> >
> > ftrace_caller and ftrace_regs_caller save their regs with the respective
> > option of SAVE_ABI_REGS, then call the tracing function, especially
> > graph_ops's ftrace_graph_func. So the ftrace_graph_[regs]_call labels
> > aren't needed anymore if FTRACE_WITH_REGS is defined.
> >
> > As the previous patch described, the ftrace_caller remains with its
> > ftrace_graph_call if FTRACE_WITH_REGS isn't defined,
> >
> > For convenience, the original argument setup for the tracing function in
> > ftrace_[regs]_caller is separated as PREPARE_ARGS.
> >
> > Signed-off-by: Song Shuai <suagrfillet@gmail.com>
> > Tested-by: Guo Ren <guoren@kernel.org>
> > Signed-off-by: Guo Ren <guoren@kernel.org>
> > ---
> >   arch/riscv/kernel/mcount-dyn.S | 142 ++++++++++++++++++++++++---------
> >   1 file changed, 104 insertions(+), 38 deletions(-)
> >
> > diff --git a/arch/riscv/kernel/mcount-dyn.S b/arch/riscv/kernel/mcount-dyn.S
> > index b75332ced757..d7d4d51b4bd7 100644
> > --- a/arch/riscv/kernel/mcount-dyn.S
> > +++ b/arch/riscv/kernel/mcount-dyn.S
> > @@ -57,19 +57,52 @@
> >          .endm
> >
> >   #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
> > -       .macro SAVE_ALL
> > +
> > +/**
> > +* SAVE_ABI_REGS - save regs against the pt_regs struct
> > +*
> > +* @all: tell if saving all the regs
> > +*
> > +* If all is set, all the regs will be saved, otherwise only ABI
> > +* related regs (a0-a7,epc,ra and optional s0) will be saved.
> > +*
> > +* After the stack is established,
> > +*
> > +* 0(sp) stores the PC of the traced function which can be accessed
> > +* by &(fregs)->regs->epc in tracing function. Note that the real
> > +* function entry address should be computed with -FENTRY_RA_OFFSET.
> > +*
> > +* 8(sp) stores the function return address (i.e. parent IP) that
> > +* can be accessed by &(fregs)->regs->ra in tracing function.
> > +*
> > +* The other regs are saved at the respective localtion and accessed
> > +* by the respective pt_regs member.
> > +*
> > +* Here is the layout of stack for your reference.
> > +*
> > +* PT_SIZE_ON_STACK  ->  +++++++++
> > +*                       + ..... +
> > +*                       + t3-t6 +
> > +*                       + s2-s11+
> > +*                       + a0-a7 + --++++-> ftrace_caller saved
> > +*                       + s1    +   +
> > +*                       + s0    + --+
> > +*                       + t0-t2 +   +
> > +*                       + tp    +   +
> > +*                       + gp    +   +
> > +*                       + sp    +   +
> > +*                       + ra    + --+ // parent IP
> > +*               sp  ->  + epc   + --+ // PC
> > +*                       +++++++++
> > +**/
> > +       .macro SAVE_ABI_REGS, all=0
> >          addi    sp, sp, -PT_SIZE_ON_STACK
> >
> >          REG_S t0,  PT_EPC(sp)
> >          REG_S x1,  PT_RA(sp)
> > -       REG_S x2,  PT_SP(sp)
> > -       REG_S x3,  PT_GP(sp)
> > -       REG_S x4,  PT_TP(sp)
> > -       REG_S x5,  PT_T0(sp)
> > -       REG_S x6,  PT_T1(sp)
> > -       REG_S x7,  PT_T2(sp)
> > -       REG_S x8,  PT_S0(sp)
> > -       REG_S x9,  PT_S1(sp)
> > +
> > +       // always save the ABI regs
> > +
> >          REG_S x10, PT_A0(sp)
> >          REG_S x11, PT_A1(sp)
> >          REG_S x12, PT_A2(sp)
> > @@ -78,6 +111,18 @@
> >          REG_S x15, PT_A5(sp)
> >          REG_S x16, PT_A6(sp)
> >          REG_S x17, PT_A7(sp)
> > +
> > +       // save the leftover regs
> > +
> > +       .if \all == 1
> > +       REG_S x2,  PT_SP(sp)
> > +       REG_S x3,  PT_GP(sp)
> > +       REG_S x4,  PT_TP(sp)
> > +       REG_S x5,  PT_T0(sp)
> > +       REG_S x6,  PT_T1(sp)
> > +       REG_S x7,  PT_T2(sp)
> > +       REG_S x8,  PT_S0(sp)
> > +       REG_S x9,  PT_S1(sp)
> >          REG_S x18, PT_S2(sp)
> >          REG_S x19, PT_S3(sp)
> >          REG_S x20, PT_S4(sp)
> > @@ -92,19 +137,19 @@
> >          REG_S x29, PT_T4(sp)
> >          REG_S x30, PT_T5(sp)
> >          REG_S x31, PT_T6(sp)
> > +
> > +       // save s0 if FP_TEST defined
> > +
> > +       .else
> > +#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
> > +       REG_S x8,  PT_S0(sp)
> > +#endif
> > +       .endif
> >          .endm
> >
> > -       .macro RESTORE_ALL
> > +       .macro RESTORE_ABI_REGS, all=0
> >          REG_L t0,  PT_EPC(sp)
> >          REG_L x1,  PT_RA(sp)
> > -       REG_L x2,  PT_SP(sp)
> > -       REG_L x3,  PT_GP(sp)
> > -       REG_L x4,  PT_TP(sp)
> > -       REG_L x5,  PT_T0(sp)
> > -       REG_L x6,  PT_T1(sp)
> > -       REG_L x7,  PT_T2(sp)
> > -       REG_L x8,  PT_S0(sp)
> > -       REG_L x9,  PT_S1(sp)
> >          REG_L x10, PT_A0(sp)
> >          REG_L x11, PT_A1(sp)
> >          REG_L x12, PT_A2(sp)
> > @@ -113,6 +158,16 @@
> >          REG_L x15, PT_A5(sp)
> >          REG_L x16, PT_A6(sp)
> >          REG_L x17, PT_A7(sp)
> > +
> > +       .if \all == 1
> > +       REG_L x2,  PT_SP(sp)
> > +       REG_L x3,  PT_GP(sp)
> > +       REG_L x4,  PT_TP(sp)
> > +       REG_L x5,  PT_T0(sp)
>
> Same as for the patch #3, please skip "REG_L x5,  PT_T0(sp)" here. The
> correct value of t0/x5 has already been read from PT_EPC(sp) at this point.
Oh, I don't want to do that here. It's a common macro. Because it's a
continuous load within the cacheline, I don't think it would cause a
performance gap.


>
> > +       REG_L x6,  PT_T1(sp)
> > +       REG_L x7,  PT_T2(sp)
> > +       REG_L x8,  PT_S0(sp)
> > +       REG_L x9,  PT_S1(sp)
> >          REG_L x18, PT_S2(sp)
> >          REG_L x19, PT_S3(sp)
> >          REG_L x20, PT_S4(sp)
> > @@ -128,10 +183,25 @@
> >          REG_L x30, PT_T5(sp)
> >          REG_L x31, PT_T6(sp)
> >
> > +       .else
> > +#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
> > +       REG_L x8,  PT_S0(sp)
> > +#endif
> > +       .endif
> >          addi    sp, sp, PT_SIZE_ON_STACK
> >          .endm
> > +
> > +       .macro PREPARE_ARGS
> > +       addi    a0, t0, -FENTRY_RA_OFFSET       // ip
> > +       la      a1, function_trace_op
> > +       REG_L   a2, 0(a1)                       // op
> > +       mv      a1, ra                          // parent_ip
> > +       mv      a3, sp                          // fregs
> > +       .endm
> > +
> >   #endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
> >
> > +#ifndef CONFIG_DYNAMIC_FTRACE_WITH_REGS
> >   ENTRY(ftrace_caller)
> >          SAVE_ABI
> >
> > @@ -160,33 +230,29 @@ ftrace_graph_call:
> >          jr t0
> >   ENDPROC(ftrace_caller)
> >
> > -#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
> > +#else /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
> >   ENTRY(ftrace_regs_caller)
> > -       SAVE_ALL
> > -
> > -       addi    a0, t0, -FENTRY_RA_OFFSET
> > -       la      a1, function_trace_op
> > -       REG_L   a2, 0(a1)
> > -       mv      a1, ra
> > -       mv      a3, sp
> > +       SAVE_ABI_REGS 1
> > +       PREPARE_ARGS
> >
> >   ftrace_regs_call:
> >          .global ftrace_regs_call
> >          call    ftrace_stub
> >
> > -#ifdef CONFIG_FUNCTION_GRAPH_TRACER
> > -       addi    a0, sp, PT_RA
> > -       REG_L   a1, PT_T0(sp)
> > -       addi    a1, a1, -FENTRY_RA_OFFSET
> > -#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
> > -       mv      a2, s0
> > -#endif
> > -ftrace_graph_regs_call:
> > -       .global ftrace_graph_regs_call
> > -       call    ftrace_stub
> > -#endif
> >
> > -       RESTORE_ALL
> > +       RESTORE_ABI_REGS 1
> >          jr t0
> >   ENDPROC(ftrace_regs_caller)
> > +
> > +ENTRY(ftrace_caller)
> > +       SAVE_ABI_REGS 0
> > +       PREPARE_ARGS
> > +
> > +ftrace_call:
> > +       .global ftrace_call
> > +       call    ftrace_stub
> > +
> > +       RESTORE_ABI_REGS 0
> > +       jr t0
> > +ENDPROC(ftrace_caller)
> >   #endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
> > --
> > 2.36.1
> >
> >
> Regards,
> Evgenii
>
>


--
Best Regards
 Guo Ren