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Date: Wed, 16 Nov 2022 09:45:40 +0100
From: Andrew Jones <ajones@...tanamicro.com>
To: Song Shuai <suagrfillet@...il.com>
Cc: guoren@...nel.org, rostedt@...dmis.org, mhiramat@...nel.org,
mark.rutland@....com, paul.walmsley@...ive.com, palmer@...belt.com,
aou@...s.berkeley.edu, linux-riscv@...ts.infradead.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] riscv/ftrace: SAVE_ALL supports lightweight save
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@...il.com>
> ---
> 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.
> +*
> +* 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
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