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

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Date:   Wed, 18 May 2022 10:08:48 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH v3 19/25] powerpc/ftrace: Minimise number of #ifdefs



Le 18/05/2022 à 11:45, Naveen N. Rao a écrit :
> 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:

Ah yes, it makes sense.

Initial purpose was to de-duplicate ftrace_dyn_arch_init(), but as 
ftrace_dyn_arch_init() is defined as a weak nop function in 
kernel/trace/ftrace.c we don't need it for PPC32 at all.

And then kernel_toc_addr() could remain inside #ifdef CONFIG_PPC64 in 
asm/section.h

> 
> 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