Re: [PATCH -next V6 5/7] riscv: ftrace: Make ftrace_caller call ftrace_graph_func

From: Guo Ren
Date: Wed Jan 11 2023 - 03:42:48 EST

On Wed, Jan 11, 2023 at 4:23 PM Guo Ren <guoren@xxxxxxxxxx> wrote:
>
> On Wed, Jan 11, 2023 at 1:16 AM Evgenii Shatokhin <e.shatokhin@xxxxxxxxx> wrote:
> >
> > On 07.01.2023 16:35, guoren@xxxxxxxxxx wrote:
> > > From: Song Shuai <suagrfillet@xxxxxxxxx>
> > >
> > > 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@xxxxxxxxx>
> > > Tested-by: Guo Ren <guoren@xxxxxxxxxx>
> > > Signed-off-by: Guo Ren <guoren@xxxxxxxxxx>
> > > ---
> > > 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.
I misunderstood here; you're correct. The "REG_L x5, PT_T0(sp)"
should be skipped.

>
>
> >
> > > + 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



--
Best Regards
Guo Ren