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Date:   Mon, 14 Feb 2022 23:21:56 +0530
From:   "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
Subject: Re: [PATCH v2 12/13] powerpc/ftrace: Prepare ftrace_64_mprofile.S for
 reuse by PPC32
To:     Christophe Leroy <christophe.leroy@csgroup.eu>,
        Jiri Kosina <jikos@kernel.org>,
        Joe Lawrence <joe.lawrence@redhat.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Miroslav Benes <mbenes@suse.cz>,
        Ingo Molnar <mingo@redhat.com>, Petr Mladek <pmladek@suse.com>,
        Steven Rostedt <rostedt@goodmis.org>
Cc:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
        "live-patching@vger.kernel.org" <live-patching@vger.kernel.org>
References: <cover.1640017960.git.christophe.leroy@csgroup.eu>
        <82a732915dc71ee766e31809350939331944006d.1640017960.git.christophe.leroy@csgroup.eu>
In-Reply-To: <82a732915dc71ee766e31809350939331944006d.1640017960.git.christophe.leroy@csgroup.eu>
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Christophe Leroy wrote:
> PPC64 mprofile versions and PPC32 are very similar.
>=20
> Modify PPC64 version so that if can be reused for PPC32.
>=20
> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> ---
>  .../powerpc/kernel/trace/ftrace_64_mprofile.S | 73 +++++++++++++------
>  1 file changed, 51 insertions(+), 22 deletions(-)

While I agree that ppc32 and -mprofile-kernel ftrace code are very=20
similar, I think this patch adds way too many #ifdefs. IMHO, this
makes the resultant code quite difficult to follow.


- Naveen

>=20
> diff --git a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S b/arch/powerp=
c/kernel/trace/ftrace_64_mprofile.S
> index 6071e0122797..56da60e98327 100644
> --- a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
> +++ b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
> @@ -34,13 +34,16 @@
>   */
>  _GLOBAL(ftrace_regs_caller)
>  	/* Save the original return address in A's stack frame */
> -	std	r0,LRSAVE(r1)
> +#ifdef CONFIG_MPROFILE_KERNEL
> +	PPC_STL	r0,LRSAVE(r1)
> +#endif
> =20
>  	/* Create our stack frame + pt_regs */
> -	stdu	r1,-SWITCH_FRAME_SIZE(r1)
> +	PPC_STLU	r1,-SWITCH_FRAME_SIZE(r1)
> =20
>  	/* Save all gprs to pt_regs */
>  	SAVE_GPR(0, r1)
> +#ifdef CONFIG_PPC64
>  	SAVE_GPRS(2, 11, r1)
> =20
>  	/* Ok to continue? */
> @@ -49,10 +52,13 @@ _GLOBAL(ftrace_regs_caller)
>  	beq	ftrace_no_trace
> =20
>  	SAVE_GPRS(12, 31, r1)
> +#else
> +	stmw	r2, GPR2(r1)
> +#endif
> =20
>  	/* Save previous stack pointer (r1) */
>  	addi	r8, r1, SWITCH_FRAME_SIZE
> -	std	r8, GPR1(r1)
> +	PPC_STL	r8, GPR1(r1)
> =20
>  	/* Load special regs for save below */
>  	mfmsr   r8
> @@ -63,10 +69,11 @@ _GLOBAL(ftrace_regs_caller)
>  	/* Get the _mcount() call site out of LR */
>  	mflr	r7
>  	/* Save it as pt_regs->nip */
> -	std     r7, _NIP(r1)
> +	PPC_STL	r7, _NIP(r1)
>  	/* Save the read LR in pt_regs->link */
> -	std     r0, _LINK(r1)
> +	PPC_STL	r0, _LINK(r1)
> =20
> +#ifdef CONFIG_PPC64
>  	/* Save callee's TOC in the ABI compliant location */
>  	std	r2, 24(r1)
>  	ld	r2,PACATOC(r13)	/* get kernel TOC in r2 */
> @@ -74,8 +81,12 @@ _GLOBAL(ftrace_regs_caller)
>  	addis	r3,r2,function_trace_op@toc@ha
>  	addi	r3,r3,function_trace_op@toc@l
>  	ld	r5,0(r3)
> +#else
> +	lis	r3,function_trace_op@ha
> +	lwz	r5,function_trace_op@l(r3)
> +#endif
> =20
> -#ifdef CONFIG_LIVEPATCH
> +#ifdef CONFIG_LIVEPATCH_64
>  	mr	r14,r7		/* remember old NIP */
>  #endif
>  	/* Calculate ip from nip-4 into r3 for call below */
> @@ -85,10 +96,10 @@ _GLOBAL(ftrace_regs_caller)
>  	mr	r4, r0
> =20
>  	/* Save special regs */
> -	std     r8, _MSR(r1)
> -	std     r9, _CTR(r1)
> -	std     r10, _XER(r1)
> -	std     r11, _CCR(r1)
> +	PPC_STL	r8, _MSR(r1)
> +	PPC_STL	r9, _CTR(r1)
> +	PPC_STL	r10, _XER(r1)
> +	PPC_STL	r11, _CCR(r1)
> =20
>  	/* Load &pt_regs in r6 for call below */
>  	addi    r6, r1 ,STACK_FRAME_OVERHEAD
> @@ -100,27 +111,32 @@ ftrace_regs_call:
>  	nop
> =20
>  	/* Load ctr with the possibly modified NIP */
> -	ld	r3, _NIP(r1)
> +	PPC_LL	r3, _NIP(r1)
>  	mtctr	r3
> -#ifdef CONFIG_LIVEPATCH
> +#ifdef CONFIG_LIVEPATCH_64
>  	cmpd	r14, r3		/* has NIP been altered? */
>  #endif
> =20
>  	/* Restore gprs */
> -	REST_GPR(0, r1)
> +#ifdef CONFIG_PPC64
>  	REST_GPRS(2, 31, r1)
> +#else
> +	lmw	r2, GPR2(r1)
> +#endif
> =20
>  	/* Restore possibly modified LR */
> -	ld	r0, _LINK(r1)
> +	PPC_LL	r0, _LINK(r1)
>  	mtlr	r0
> =20
> +#ifdef CONFIG_PPC64
>  	/* Restore callee's TOC */
>  	ld	r2, 24(r1)
> +#endif
> =20
>  	/* Pop our stack frame */
>  	addi r1, r1, SWITCH_FRAME_SIZE
> =20
> -#ifdef CONFIG_LIVEPATCH
> +#ifdef CONFIG_LIVEPATCH_64
>          /* Based on the cmpd above, if the NIP was altered handle livepa=
tch */
>  	bne-	livepatch_handler
>  #endif
> @@ -129,6 +145,7 @@ ftrace_regs_call:
>  _GLOBAL(ftrace_stub)
>  	blr
> =20
> +#ifdef CONFIG_PPC64
>  ftrace_no_trace:
>  	mflr	r3
>  	mtctr	r3
> @@ -136,25 +153,31 @@ ftrace_no_trace:
>  	addi	r1, r1, SWITCH_FRAME_SIZE
>  	mtlr	r0
>  	bctr
> +#endif
> =20
>  _GLOBAL(ftrace_caller)
>  	/* Save the original return address in A's stack frame */
> -	std	r0, LRSAVE(r1)
> +#ifdef CONFIG_MPROFILE_KERNEL
> +	PPC_STL	r0, LRSAVE(r1)
> +#endif
> =20
>  	/* Create our stack frame + pt_regs */
> -	stdu	r1, -SWITCH_FRAME_SIZE(r1)
> +	PPC_STLU	r1, -SWITCH_FRAME_SIZE(r1)
> =20
>  	/* Save all gprs to pt_regs */
>  	SAVE_GPRS(3, 10, r1)
> =20
> +#ifdef CONFIG_PPC64
>  	lbz	r3, PACA_FTRACE_ENABLED(r13)
>  	cmpdi	r3, 0
>  	beq	ftrace_no_trace
> +#endif
> =20
>  	/* Get the _mcount() call site out of LR */
>  	mflr	r7
> -	std     r7, _NIP(r1)
> +	PPC_STL     r7, _NIP(r1)
> =20
> +#ifdef CONFIG_PPC64
>  	/* Save callee's TOC in the ABI compliant location */
>  	std	r2, 24(r1)
>  	ld	r2, PACATOC(r13)	/* get kernel TOC in r2 */
> @@ -162,6 +185,10 @@ _GLOBAL(ftrace_caller)
>  	addis	r3, r2, function_trace_op@toc@ha
>  	addi	r3, r3, function_trace_op@toc@l
>  	ld	r5, 0(r3)
> +#else
> +	lis	r3,function_trace_op@ha
> +	lwz	r5,function_trace_op@l(r3)
> +#endif
> =20
>  #ifdef CONFIG_LIVEPATCH_64
>  	SAVE_GPR(14, r1)
> @@ -171,7 +198,7 @@ _GLOBAL(ftrace_caller)
>  	subi    r3, r7, MCOUNT_INSN_SIZE
> =20
>  	/* Put the original return address in r4 as parent_ip */
> -	std	r0, _LINK(r1)
> +	PPC_STL	r0, _LINK(r1)
>  	mr	r4, r0
> =20
>  	/* Load &pt_regs in r6 for call below */
> @@ -183,7 +210,7 @@ ftrace_call:
>  	bl	ftrace_stub
>  	nop
> =20
> -	ld	r3, _NIP(r1)
> +	PPC_LL	r3, _NIP(r1)
>  	mtctr	r3
>  #ifdef CONFIG_LIVEPATCH_64
>  	cmpd	r14, r3		/* has NIP been altered? */
> @@ -193,11 +220,13 @@ ftrace_call:
>  	/* Restore gprs */
>  	REST_GPRS(3, 10, r1)
> =20
> +#ifdef CONFIG_PPC64
>  	/* Restore callee's TOC */
>  	ld	r2, 24(r1)
> +#endif
> =20
>  	/* Restore possibly modified LR */
> -	ld	r0, _LINK(r1)
> +	PPC_LL	r0, _LINK(r1)
>  	mtlr	r0
> =20
>  	/* Pop our stack frame */
> @@ -209,7 +238,7 @@ ftrace_call:
>  #endif
>  	bctr			/* jump after _mcount site */
> =20
> -#ifdef CONFIG_LIVEPATCH
> +#ifdef CONFIG_LIVEPATCH_64
>  	/*
>  	 * This function runs in the mcount context, between two functions. As
>  	 * such it can only clobber registers which are volatile and used in
> --=20
> 2.33.1
>=20