linux-kernel - Re: [PATCH v1 10/22] powerpc/ftrace: Use CONFIG_FUNCTION_TRACER instead of CONFIG_DYNAMIC

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Message-ID: <a02d74de-7714-3b6a-ef05-d18aec6039ba@csgroup.eu>
Date:   Fri, 6 May 2022 11:41:02 +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>,
        Ingo Molnar <mingo@...hat.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>,
        Steven Rostedt <rostedt@...dmis.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 v1 10/22] powerpc/ftrace: Use CONFIG_FUNCTION_TRACER
 instead of CONFIG_DYNAMIC_FTRACE



Le 18/04/2022 à 09:00, Naveen N. Rao a écrit :
> 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.
>>
>> 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.
>>
>> As CONFIG_FUNCTION_GRAPH_TRACER depends on CONFIG_FUNCTION_TRACER,
>> ftrace.o doesn't need to appear for both symbols in Makefile.
>>
>> 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 
> needed in ftrace.c

Ok, added to the commit message

> 
>> ifdef CONFIG_FUNCTION_TRACER is not needed in ftrace.c
>>
>> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.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(-)
>>
>> 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_SWITCH) ||\
>> -    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_SWITCH) || \
>> -    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 */
>>
>> -#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
>>
>> -#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/include/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_SWITCH) ||\
>> -    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 = rela[i].r_addend;
>>          }
>>
>> -#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;
>>  }
>>
>> -#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,
>>          }
>>      }
>>
>> -#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;
>>  }
>>
>> -#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 sense, 
> but I'm not sure the above changes are necessary.
> 
> For generic code (outside arch/powerpc/kernel/trace), I think it is good 
> to retain the actual dependency which is DYNAMIC_FTRACE. In my view, 
> gating some of the above code on FUNCTION_TRACER is also confusing. The 
> primary implication of always selecting DYNAMIC_FTRACE is within the 
> powerpc trace code, and it is good to keep it that way.

Ok I keep only the changes to trace directory for now.

> 
>> diff --git a/arch/powerpc/kernel/trace/Makefile 
>> b/arch/powerpc/kernel/trace/Makefile
>> index fc32ec30b297..af8527538fe4 100644
>> --- a/arch/powerpc/kernel/trace/Makefile
>> +++ b/arch/powerpc/kernel/trace/Makefile
>> @@ -14,9 +14,7 @@ obj64-$(CONFIG_FUNCTION_TRACER)        += 
>> ftrace_mprofile.o
>>  else
>>  obj64-$(CONFIG_FUNCTION_TRACER)        += ftrace_64_pg.o
>>  endif
>> -obj-$(CONFIG_FUNCTION_TRACER)        += ftrace_low.o
>> -obj-$(CONFIG_DYNAMIC_FTRACE)        += ftrace.o
>> -obj-$(CONFIG_FUNCTION_GRAPH_TRACER)    += ftrace.o
>> +obj-$(CONFIG_FUNCTION_TRACER)        += ftrace_low.o ftrace.o
>>  obj-$(CONFIG_TRACING)            += trace_clock.o
>>
>>  obj-$(CONFIG_PPC64)            += $(obj64-y)
>> diff --git a/arch/powerpc/kernel/trace/ftrace.c 
>> b/arch/powerpc/kernel/trace/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>
>>
>> -
>> -#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 */
>>
>>  #ifdef CONFIG_FUNCTION_GRAPH_TRACER
>>
>> -- 
>> 2.35.1
>>
> 
> - Naveen