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Date:   Mon, 18 Apr 2022 12:30:09 +0530
From:   "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
Subject: Re: [PATCH v1 10/22] powerpc/ftrace: Use CONFIG_FUNCTION_TRACER
 instead of CONFIG_DYNAMIC_FTRACE
To:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Christophe Leroy <christophe.leroy@csgroup.eu>,
        Ingo Molnar <mingo@redhat.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Paul Mackerras <paulus@samba.org>,
        Steven Rostedt <rostedt@goodmis.org>
Cc:     linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
References: <cover.1648131740.git.christophe.leroy@csgroup.eu>
        <72070995f96acaa9a387963e3848bd24a436a847.1648131740.git.christophe.leroy@csgroup.eu>
In-Reply-To: <72070995f96acaa9a387963e3848bd24a436a847.1648131740.git.christophe.leroy@csgroup.eu>
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Christophe Leroy wrote:
> Since commit 0c0c52306f47 ("powerpc: Only support DYNAMIC_FTRACE not
> static"), CONFIG_DYNAMIC_FTRACE is always selected when
> CONFIG_FUNCTION_TRACER is selected.
>=20
> To avoid confusion and have the reader wonder what's happen when
> CONFIG_FUNCTION_TRACER is selected and CONFIG_DYNAMIC_FTRACE is not,
> use CONFIG_FUNCTION_TRACER in ifdefs instead of CONFIG_DYNAMIC_FTRACE.
>=20
> As CONFIG_FUNCTION_GRAPH_TRACER depends on CONFIG_FUNCTION_TRACER,
> ftrace.o doesn't need to appear for both symbols in Makefile.
>=20
> Then as ftrace.o is built only when CONFIG_FUNCTION_TRACER is selected

and since it implies CONFIG_DYNAMIC_FTRACE, CONFIG_DYNAMIC_FTRACE is not=20
needed in ftrace.c

> ifdef CONFIG_FUNCTION_TRACER is not needed in ftrace.c
>=20
> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> ---
>  arch/powerpc/include/asm/book3s/32/pgtable.h | 2 +-
>  arch/powerpc/include/asm/book3s/64/pgtable.h | 2 +-
>  arch/powerpc/include/asm/module.h            | 4 ++--
>  arch/powerpc/include/asm/nohash/pgtable.h    | 2 +-
>  arch/powerpc/kernel/module_32.c              | 4 ++--
>  arch/powerpc/kernel/module_64.c              | 6 +++---
>  arch/powerpc/kernel/trace/Makefile           | 4 +---
>  arch/powerpc/kernel/trace/ftrace.c           | 4 ----
>  8 files changed, 11 insertions(+), 17 deletions(-)
>=20
> diff --git a/arch/powerpc/include/asm/book3s/32/pgtable.h b/arch/powerpc/=
include/asm/book3s/32/pgtable.h
> index 772e00dc4ef1..992aed626eb4 100644
> --- a/arch/powerpc/include/asm/book3s/32/pgtable.h
> +++ b/arch/powerpc/include/asm/book3s/32/pgtable.h
> @@ -124,7 +124,7 @@ static inline bool pte_user(pte_t pte)
>   * on platforms where such control is possible.
>   */
>  #if defined(CONFIG_KGDB) || defined(CONFIG_XMON) || defined(CONFIG_BDI_S=
WITCH) ||\
> -	defined(CONFIG_KPROBES) || defined(CONFIG_DYNAMIC_FTRACE)
> +	defined(CONFIG_KPROBES) || defined(CONFIG_FUNCTION_TRACER)
>  #define PAGE_KERNEL_TEXT	PAGE_KERNEL_X
>  #else
>  #define PAGE_KERNEL_TEXT	PAGE_KERNEL_ROX
> diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/=
include/asm/book3s/64/pgtable.h
> index 875730d5af40..cf01b609572f 100644
> --- a/arch/powerpc/include/asm/book3s/64/pgtable.h
> +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
> @@ -169,7 +169,7 @@
>   * on platforms where such control is possible.
>   */
>  #if defined(CONFIG_KGDB) || defined(CONFIG_XMON) || defined(CONFIG_BDI_S=
WITCH) || \
> -	defined(CONFIG_KPROBES) || defined(CONFIG_DYNAMIC_FTRACE)
> +	defined(CONFIG_KPROBES) || defined(CONFIG_FUNCTION_TRACER)
>  #define PAGE_KERNEL_TEXT	PAGE_KERNEL_X
>  #else
>  #define PAGE_KERNEL_TEXT	PAGE_KERNEL_ROX
> diff --git a/arch/powerpc/include/asm/module.h b/arch/powerpc/include/asm=
/module.h
> index 857d9ff24295..e6f5963fd96e 100644
> --- a/arch/powerpc/include/asm/module.h
> +++ b/arch/powerpc/include/asm/module.h
> @@ -39,7 +39,7 @@ struct mod_arch_specific {
>  	unsigned int init_plt_section;
>  #endif /* powerpc64 */
>=20
> -#ifdef CONFIG_DYNAMIC_FTRACE
> +#ifdef CONFIG_FUNCTION_TRACER
>  	unsigned long tramp;
>  #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
>  	unsigned long tramp_regs;
> @@ -68,7 +68,7 @@ struct mod_arch_specific {
>  #    endif	/* MODULE */
>  #endif
>=20
> -#ifdef CONFIG_DYNAMIC_FTRACE
> +#ifdef CONFIG_FUNCTION_TRACER
>  #    ifdef MODULE
>  	asm(".section .ftrace.tramp,\"ax\",@nobits; .align 3; .previous");
>  #    endif	/* MODULE */
> diff --git a/arch/powerpc/include/asm/nohash/pgtable.h b/arch/powerpc/inc=
lude/asm/nohash/pgtable.h
> index ac75f4ab0dba..2e8cf217a191 100644
> --- a/arch/powerpc/include/asm/nohash/pgtable.h
> +++ b/arch/powerpc/include/asm/nohash/pgtable.h
> @@ -23,7 +23,7 @@
>   * on platforms where such control is possible.
>   */
>  #if defined(CONFIG_KGDB) || defined(CONFIG_XMON) || defined(CONFIG_BDI_S=
WITCH) ||\
> -	defined(CONFIG_KPROBES) || defined(CONFIG_DYNAMIC_FTRACE)
> +	defined(CONFIG_KPROBES) || defined(CONFIG_FUNCTION_TRACER)
>  #define PAGE_KERNEL_TEXT	PAGE_KERNEL_X
>  #else
>  #define PAGE_KERNEL_TEXT	PAGE_KERNEL_ROX
> diff --git a/arch/powerpc/kernel/module_32.c b/arch/powerpc/kernel/module=
_32.c
> index a0432ef46967..2aa368ce21c9 100644
> --- a/arch/powerpc/kernel/module_32.c
> +++ b/arch/powerpc/kernel/module_32.c
> @@ -39,7 +39,7 @@ static unsigned int count_relocs(const Elf32_Rela *rela=
, unsigned int num)
>  			r_addend =3D rela[i].r_addend;
>  		}
>=20
> -#ifdef CONFIG_DYNAMIC_FTRACE
> +#ifdef CONFIG_FUNCTION_TRACER
>  	_count_relocs++;	/* add one for ftrace_caller */
>  #endif
>  	return _count_relocs;
> @@ -288,7 +288,7 @@ int apply_relocate_add(Elf32_Shdr *sechdrs,
>  	return 0;
>  }
>=20
> -#ifdef CONFIG_DYNAMIC_FTRACE
> +#ifdef CONFIG_FUNCTION_TRACER
>  int module_trampoline_target(struct module *mod, unsigned long addr,
>  			     unsigned long *target)
>  {
> diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module=
_64.c
> index 794720530442..b13a72665eee 100644
> --- a/arch/powerpc/kernel/module_64.c
> +++ b/arch/powerpc/kernel/module_64.c
> @@ -207,7 +207,7 @@ static unsigned long get_stubs_size(const Elf64_Ehdr =
*hdr,
>  		}
>  	}
>=20
> -#ifdef CONFIG_DYNAMIC_FTRACE
> +#ifdef CONFIG_FUNCTION_TRACER
>  	/* make the trampoline to the ftrace_caller */
>  	relocs++;
>  #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
> @@ -372,7 +372,7 @@ static bool is_mprofile_ftrace_call(const char *name)
>  {
>  	if (!strcmp("_mcount", name))
>  		return true;
> -#ifdef CONFIG_DYNAMIC_FTRACE
> +#ifdef CONFIG_FUNCTION_TRACER
>  	if (!strcmp("ftrace_caller", name))
>  		return true;
>  #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
> @@ -740,7 +740,7 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
>  	return 0;
>  }
>=20
> -#ifdef CONFIG_DYNAMIC_FTRACE
> +#ifdef CONFIG_FUNCTION_TRACER
>  int module_trampoline_target(struct module *mod, unsigned long addr,
>  			     unsigned long *target)
>  {

The below two changes to trace/Makefile and trace/ftrace.c make=20
sense, but I'm not sure the above changes are necessary.

For generic code (outside arch/powerpc/kernel/trace), I think it is good=20
to retain the actual dependency which is DYNAMIC_FTRACE. In my view,=20
gating some of the above code on FUNCTION_TRACER is also confusing. The=20
primary implication of always selecting DYNAMIC_FTRACE is within the=20
powerpc trace code, and it is good to keep it that way.

> diff --git a/arch/powerpc/kernel/trace/Makefile b/arch/powerpc/kernel/tra=
ce/Makefile
> index fc32ec30b297..af8527538fe4 100644
> --- a/arch/powerpc/kernel/trace/Makefile
> +++ b/arch/powerpc/kernel/trace/Makefile
> @@ -14,9 +14,7 @@ obj64-$(CONFIG_FUNCTION_TRACER)		+=3D ftrace_mprofile.o
>  else
>  obj64-$(CONFIG_FUNCTION_TRACER)		+=3D ftrace_64_pg.o
>  endif
> -obj-$(CONFIG_FUNCTION_TRACER)		+=3D ftrace_low.o
> -obj-$(CONFIG_DYNAMIC_FTRACE)		+=3D ftrace.o
> -obj-$(CONFIG_FUNCTION_GRAPH_TRACER)	+=3D ftrace.o
> +obj-$(CONFIG_FUNCTION_TRACER)		+=3D ftrace_low.o ftrace.o
>  obj-$(CONFIG_TRACING)			+=3D trace_clock.o
>=20
>  obj-$(CONFIG_PPC64)			+=3D $(obj64-y)
> diff --git a/arch/powerpc/kernel/trace/ftrace.c b/arch/powerpc/kernel/tra=
ce/ftrace.c
> index 2c7e42e439bb..188f59f4ee4a 100644
> --- a/arch/powerpc/kernel/trace/ftrace.c
> +++ b/arch/powerpc/kernel/trace/ftrace.c
> @@ -28,9 +28,6 @@
>  #include <asm/syscall.h>
>  #include <asm/inst.h>
>=20
> -
> -#ifdef CONFIG_DYNAMIC_FTRACE
> -
>  /*
>   * We generally only have a single long_branch tramp and at most 2 or 3 =
plt
>   * tramps generated. But, we don't use the plt tramps currently. We also=
 allot
> @@ -783,7 +780,6 @@ int __init ftrace_dyn_arch_init(void)
>  	return 0;
>  }
>  #endif
> -#endif /* CONFIG_DYNAMIC_FTRACE */
>=20
>  #ifdef CONFIG_FUNCTION_GRAPH_TRACER
>=20
> --=20
> 2.35.1
>=20

- Naveen