Re: [PATCH v2 2/3] riscv/ftrace: SAVE_ALL supports lightweight save

From: Guo Ren
Date: Wed Nov 16 2022 - 20:56:00 EST

On Wed, Nov 16, 2022 at 4:45 PM Andrew Jones <ajones@xxxxxxxxxxxxxxxx> wrote:
>
> On Wed, Nov 16, 2022 at 11:13:04AM +0800, Song Shuai wrote:
> > 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
> > introduces a lightweight option for SAVE_ALL to save only the necessary
> > regs for ftrace_caller.
> >
> > For convenience, the original argument setup for the tracing function in
> > ftrace_[regs]_caller is killed and appended to the tail of SAVE_ALL.
> >
> > Signed-off-by: Song Shuai <suagrfillet@xxxxxxxxx>
> > ---
> > arch/riscv/kernel/mcount-dyn.S | 110 +++++++++++++++++++++++++++------
> > 1 file changed, 92 insertions(+), 18 deletions(-)
> >
> > diff --git a/arch/riscv/kernel/mcount-dyn.S b/arch/riscv/kernel/mcount-dyn.S
> > index d171eca623b6..2f0a280bd7a0 100644
> > --- a/arch/riscv/kernel/mcount-dyn.S
> > +++ b/arch/riscv/kernel/mcount-dyn.S
> > @@ -56,7 +56,51 @@
> > .endm
> >
> > #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
> > - .macro SAVE_ALL
> > +
> > +/**
> > +* SAVE_ALL - save regs against the pt_regs struct
> > +*
> > +* @all: tell if saving all the regs
>
> I find it odd to have a macro name that includes 'ALL' in it
> to require a parameter 'all' to be set in order to actually save
> all. I suggest renaming the macro to something like SAVE_REGS.
SAVE_ABI_REGS <arg>
arg = 0 -> SAVE_ABI in pt_regs
arg = 1 -> SAVE_REGS

SAVE_ABI_REGS keeps the pt_regs layout and needs more stack space than SAVE_ABI.

>
> > +*
> > +* 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.
> > +*
> > +* For convenience the argument setup for tracing function is appended here.
> > +* Especially $sp is passed as the 4th argument of the tracing function.
> > +*
> > +* 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.
> > +*
> > +*
> > +* =========
> > +* | pip |
> > +* 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 of the traced function
> > +* +++++++++
> > +**/
> > + .macro SAVE_ALL, all=0
> > addi sp, sp, -SZREG
> > addi sp, sp, -PT_SIZE_ON_STACK
> >
> > @@ -67,14 +111,8 @@
> > REG_S x1, PT_RA(sp)
> > REG_L x1, PT_EPC(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)
> > @@ -83,6 +121,18 @@
> > REG_S x15, PT_A5(sp)
> > REG_S x16, PT_A6(sp)
> > REG_S x17, PT_A7(sp)
> > +
> > + /* save leftover regs for ftrace_regs_caller*/
> > +
> > + .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)
> > @@ -97,22 +147,31 @@
> > REG_S x29, PT_T4(sp)
> > REG_S x30, PT_T5(sp)
> > REG_S x31, PT_T6(sp)
> > + .else
> > +
> > + /* save s0 for ftrace_caller if FP_TEST defined */
> > +
> > +#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
> > + REG_S x8, PT_S0(sp)
> > +#endif
> > + .endif
> > +
> > + /* setup 4 args for tracing functions */
> > +
> > + addi a0, ra, -FENTRY_RA_OFFSET // ip
> > + la a1, function_trace_op
> > + REG_L a2, 0(a1) // op
> > + REG_L a1, PT_SIZE_ON_STACK(sp) // parent_ip
> > + mv a3, sp // fregs
>
> Please line up the comments.
>
> > .endm
> >
> > - .macro RESTORE_ALL
> > + .macro RESTORE_ALL, all=0
> > REG_L x1, PT_RA(sp)
> > addi sp, sp, PT_SIZE_ON_STACK
> > REG_S x1, (sp)
> > addi sp, sp, -PT_SIZE_ON_STACK
> > REG_L x1, PT_EPC(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)
> > @@ -121,6 +180,16 @@
> > 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)
> > + 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)
> > @@ -136,6 +205,11 @@
> > 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
> > addi sp, sp, SZREG
> > .endm
> > --
> > 2.20.1
> >
> >
>
> Thanks,
> drew



--
Best Regards
Guo Ren