Re: [PATCH v4 1/9] ppc64 (le): prepare for -mprofile-kernel

[Denis Kirjanov]

On 11/25/15, Torsten Duwe <duwe@xxxxxx> wrote:
> The gcc switch -mprofile-kernel, available for ppc64 on gcc > 4.8.5,
> allows to call _mcount very early in the function, which low-level
> ASM code and code patching functions need to consider.
> Especially the link register and the parameter registers are still
> alive and not yet saved into a new stack frame.
>
> Signed-off-by: Torsten Duwe <duwe@xxxxxxx>
> ---
>  arch/powerpc/kernel/entry_64.S  | 44
> +++++++++++++++++++++++++++++++++++++++--
>  arch/powerpc/kernel/ftrace.c    | 12 +++++++++--
>  arch/powerpc/kernel/module_64.c | 13 ++++++++++++
>  3 files changed, 65 insertions(+), 4 deletions(-)
>
> diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
> index a94f155..8d56b16 100644
> --- a/arch/powerpc/kernel/entry_64.S
> +++ b/arch/powerpc/kernel/entry_64.S
> @@ -1206,7 +1206,11 @@ _GLOBAL(enter_prom)
>  #ifdef CONFIG_DYNAMIC_FTRACE
>  _GLOBAL(mcount)
>  _GLOBAL(_mcount)
> -	blr
> +	mflr	r0
> +	mtctr	r0
> +	ld	r0,LRSAVE(r1)
> +	mtlr	r0
> +	bctr
>
>  _GLOBAL_TOC(ftrace_caller)
>  	/* Taken from output of objdump from lib64/glibc */
> @@ -1262,13 +1266,28 @@ _GLOBAL(ftrace_stub)
>
>  #ifdef CONFIG_FUNCTION_GRAPH_TRACER
>  _GLOBAL(ftrace_graph_caller)
> +#ifdef CC_USING_MPROFILE_KERNEL
> +	// with -mprofile-kernel, parameter regs are still alive at _mcount
> +	std	r10, 104(r1)
> +	std	r9, 96(r1)
> +	std	r8, 88(r1)
> +	std	r7, 80(r1)
> +	std	r6, 72(r1)
> +	std	r5, 64(r1)
> +	std	r4, 56(r1)
> +	std	r3, 48(r1)
> +	mfctr	r4		// ftrace_caller has moved local addr here
> +	std	r4, 40(r1)
> +	mflr	r3		// ftrace_caller has restored LR from stack
> +#else
>  	/* load r4 with local address */
>  	ld	r4, 128(r1)
> -	subi	r4, r4, MCOUNT_INSN_SIZE
>
>  	/* Grab the LR out of the caller stack frame */
>  	ld	r11, 112(r1)
>  	ld	r3, 16(r11)
> +#endif
> +	subi	r4, r4, MCOUNT_INSN_SIZE
>
>  	bl	prepare_ftrace_return
>  	nop
> @@ -1277,6 +1296,26 @@ _GLOBAL(ftrace_graph_caller)
>  	 * prepare_ftrace_return gives us the address we divert to.
>  	 * Change the LR in the callers stack frame to this.
>  	 */
> +
> +#ifdef CC_USING_MPROFILE_KERNEL
> +	mtlr	r3
> +
> +	ld	r0, 40(r1)
> +	mtctr	r0
> +	ld	r10, 104(r1)
> +	ld	r9, 96(r1)
> +	ld	r8, 88(r1)
> +	ld	r7, 80(r1)
> +	ld	r6, 72(r1)
> +	ld	r5, 64(r1)
> +	ld	r4, 56(r1)
> +	ld	r3, 48(r1)
> +
> +	addi	r1, r1, 112
> +	mflr	r0
> +	std	r0, LRSAVE(r1)
> +	bctr
> +#else
>  	ld	r11, 112(r1)
>  	std	r3, 16(r11)
>
> @@ -1284,6 +1323,7 @@ _GLOBAL(ftrace_graph_caller)
>  	mtlr	r0
>  	addi	r1, r1, 112
>  	blr
> +#endif
>
>  _GLOBAL(return_to_handler)
>  	/* need to save return values */
> diff --git a/arch/powerpc/kernel/ftrace.c b/arch/powerpc/kernel/ftrace.c
> index 44d4d8e..080c525 100644
> --- a/arch/powerpc/kernel/ftrace.c
> +++ b/arch/powerpc/kernel/ftrace.c
> @@ -306,11 +306,19 @@ __ftrace_make_call(struct dyn_ftrace *rec, unsigned
> long addr)
>  	 * The load offset is different depending on the ABI. For simplicity
>  	 * just mask it out when doing the compare.
>  	 */
> +#ifndef CC_USING_MPROFILE_KERNEL
>  	if ((op[0] != 0x48000008) || ((op[1] & 0xffff0000) != 0xe8410000)) {
> -		pr_err("Unexpected call sequence: %x %x\n", op[0], op[1]);
> +		pr_err("Unexpected call sequence at %p: %x %x\n",
> +		ip, op[0], op[1]);
>  		return -EINVAL;
>  	}
> -
> +#else
> +	/* look for patched "NOP" on ppc64 with -mprofile-kernel */
> +	if (op[0] != 0x60000000) {
> +		pr_err("Unexpected call at %p: %x\n", ip, op[0]);
> +		return -EINVAL;
> +	}
> +#endif
>  	/* If we never set up a trampoline to ftrace_caller, then bail */
>  	if (!rec->arch.mod->arch.tramp) {
>  		pr_err("No ftrace trampoline\n");
> diff --git a/arch/powerpc/kernel/module_64.c
> b/arch/powerpc/kernel/module_64.c
> index 6838451..0819ce7 100644
> --- a/arch/powerpc/kernel/module_64.c
> +++ b/arch/powerpc/kernel/module_64.c
> @@ -475,6 +475,19 @@ static unsigned long stub_for_addr(Elf64_Shdr *sechdrs,
>  static int restore_r2(u32 *instruction, struct module *me)
>  {
>  	if (*instruction != PPC_INST_NOP) {
> +#ifdef CC_USING_MPROFILE_KERNEL
> +		/* -mprofile_kernel sequence starting with
> +		 * mflr r0; std r0, LRSAVE(r1)
> +		 */
> +		if (instruction[-3] == 0x7c0802a6 &&
> +		    instruction[-2] == 0xf8010010) {
> +			/* Nothing to be done here, it's an _mcount
> +			 * call location and r2 will have to be
> +			 * restored in the _mcount function.
> +			 */
> +			return 2;
I didn't find where you check for this return value.
> +		};
> +#endif
>  		pr_err("%s: Expect noop after relocate, got %08x\n",
>  		       me->name, *instruction);
>  		return 0;
> --
> 1.8.5.6
>
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