linux-kernel - Re: [PATCH v3 19/25] powerpc/ftrace: Minimise number of #ifdefs

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Date:   Wed, 18 May 2022 15:15:40 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v3 19/25] powerpc/ftrace: Minimise number of #ifdefs

Christophe Leroy wrote:
> A lot of #ifdefs can be replaced by IS_ENABLED()
> 
> Do so.
> 
> This requires to have kernel_toc_addr() defined at all time
> as well as PPC_INST_LD_TOC and PPC_INST_STD_LR.
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> ---
> v2: Moved the setup of pop outside of the big if()/else() in __ftrace_make_nop()
> ---
>  arch/powerpc/include/asm/code-patching.h |   2 -
>  arch/powerpc/include/asm/module.h        |   2 -
>  arch/powerpc/include/asm/sections.h      |  24 +--
>  arch/powerpc/kernel/trace/ftrace.c       | 182 +++++++++++------------
>  4 files changed, 103 insertions(+), 107 deletions(-)
> 

<snip>

> @@ -710,6 +707,9 @@ void arch_ftrace_update_code(int command)
> 
>  #ifdef CONFIG_PPC64
>  #define PACATOC offsetof(struct paca_struct, kernel_toc)
> +#else
> +#define PACATOC 0
> +#endif

This conflicts with my fix for the ftrace init tramp:
https://patchwork.ozlabs.org/project/linuxppc-dev/patch/20220516071422.463738-1-naveen.n.rao@linux.vnet.ibm.com/

It probably makes sense to retain #ifdef CONFIG_PPC64, so that we can 
get rid of the PACATOC. Here is an incremental diff:

diff --git a/arch/powerpc/kernel/trace/ftrace.c b/arch/powerpc/kernel/trace/ftrace.c
index da1a2f8ebb72f3..28169a1ccc7377 100644
--- a/arch/powerpc/kernel/trace/ftrace.c
+++ b/arch/powerpc/kernel/trace/ftrace.c
@@ -701,11 +701,6 @@ void arch_ftrace_update_code(int command)
 }
 
 #ifdef CONFIG_PPC64
-#define PACATOC offsetof(struct paca_struct, kernel_toc)
-#else
-#define PACATOC 0
-#endif
-
 extern unsigned int ftrace_tramp_text[], ftrace_tramp_init[];
 
 void ftrace_free_init_tramp(void)
@@ -724,7 +719,7 @@ int __init ftrace_dyn_arch_init(void)
 	int i;
 	unsigned int *tramp[] = { ftrace_tramp_text, ftrace_tramp_init };
 	u32 stub_insns[] = {
-		PPC_RAW_LD(_R12, _R13, PACATOC),
+		PPC_RAW_LD(_R12, _R13, offsetof(struct paca_struct, kernel_toc)),
 		PPC_RAW_ADDIS(_R12, _R12, 0),
 		PPC_RAW_ADDI(_R12, _R12, 0),
 		PPC_RAW_MTCTR(_R12),
@@ -733,9 +728,6 @@ int __init ftrace_dyn_arch_init(void)
 	unsigned long addr;
 	long reladdr;
 
-	if (IS_ENABLED(CONFIG_PPC32))
-		return 0;
-
 	addr = ppc_global_function_entry((void *)FTRACE_REGS_ADDR);
 	reladdr = addr - kernel_toc_addr();
 
@@ -754,6 +746,7 @@ int __init ftrace_dyn_arch_init(void)
 
 	return 0;
 }
+#endif
 
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 

- Naveen