linux-kernel - Re: [PATCHv2 2/8] module/ftrace: handle patchable-function-entry

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Date:   Mon, 4 Nov 2019 21:58:26 +0100
From:   Helge Deller <deller@....de>
To:     Mark Rutland <mark.rutland@....com>,
        linux-arm-kernel@...ts.infradead.org, Jessica Yu <jeyu@...nel.org>,
        "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>
Cc:     linux-kernel@...r.kernel.org, amit.kachhap@....com,
        catalin.marinas@....com, duwe@...e.de, james.morse@....com,
        jpoimboe@...hat.com, jthierry@...hat.com,
        linux-parisc@...r.kernel.org, mingo@...hat.com,
        peterz@...radead.org, rostedt@...dmis.org, svens@...ckframe.org,
        takahiro.akashi@...aro.org, will@...nel.org
Subject: Re: [PATCHv2 2/8] module/ftrace: handle patchable-function-entry

Hi Mark,

On 04.11.19 16:51, Mark Rutland wrote:
> Hi Jessica, Helge,
>
> Are you ok with the module and parisc changes, repectively?

Sure, please add my:
Acked-by: Helge Deller <deller@....de>

Helge

> The kbuild test robot is happy building this for multiple architectures,
> Sven has tested that this works correctly on parisc, and others have
> tested other architectures.
>
> I'd like to queue this in the arm64 tree soon if possible.
>
> Thanks,
> Mark.
>
> On Tue, Oct 29, 2019 at 04:58:26PM +0000, Mark Rutland wrote:
>> When using patchable-function-entry, the compiler will record the
>> callsites into a section named "__patchable_function_entries" rather
>> than "__mcount_loc". Let's abstract this difference behind a new
>> FTRACE_CALLSITE_SECTION, so that architectures don't have to handle this
>> explicitly (e.g. with custom module linker scripts).
>>
>> As parisc currently handles this explicitly, it is fixed up accordingly,
>> with its custom linker script removed. Since FTRACE_CALLSITE_SECTION is
>> only defined when DYNAMIC_FTRACE is selected, the parisc module loading
>> code is updated to only use the definition in that case. When
>> DYNAMIC_FTRACE is not selected, modules shouldn't have this section, so
>> this removes some redundant work in that case.
>>
>> I built parisc generic-{32,64}bit_defconfig with DYNAMIC_FTRACE enabled,
>> and verified that the section made it into the .ko files for modules.
>>
>> Signed-off-by: Mark Rutland <mark.rutland@....com>
>> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
>> Cc: Helge Deller <deller@....de>
>> Cc: Ingo Molnar <mingo@...hat.com>
>> Cc: James E.J. Bottomley <James.Bottomley@...senPartnership.com>
>> Cc: Jessica Yu <jeyu@...nel.org>
>> Cc: Steven Rostedt <rostedt@...dmis.org>
>> Cc: Sven Schnelle <svens@...ckframe.org>
>> Cc: linux-parisc@...r.kernel.org
>> ---
>>  arch/parisc/Makefile          |  1 -
>>  arch/parisc/kernel/module.c   | 10 +++++++---
>>  arch/parisc/kernel/module.lds |  7 -------
>>  include/linux/ftrace.h        |  5 +++++
>>  kernel/module.c               |  2 +-
>>  5 files changed, 13 insertions(+), 12 deletions(-)
>>  delete mode 100644 arch/parisc/kernel/module.lds
>>
>> diff --git a/arch/parisc/Makefile b/arch/parisc/Makefile
>> index 36b834f1c933..dca8f2de8cf5 100644
>> --- a/arch/parisc/Makefile
>> +++ b/arch/parisc/Makefile
>> @@ -60,7 +60,6 @@ KBUILD_CFLAGS += -DCC_USING_PATCHABLE_FUNCTION_ENTRY=1 \
>>  		 -DFTRACE_PATCHABLE_FUNCTION_SIZE=$(NOP_COUNT)
>>
>>  CC_FLAGS_FTRACE := -fpatchable-function-entry=$(NOP_COUNT),$(shell echo $$(($(NOP_COUNT)-1)))
>> -KBUILD_LDS_MODULE += $(srctree)/arch/parisc/kernel/module.lds
>>  endif
>>
>>  OBJCOPY_FLAGS =-O binary -R .note -R .comment -S
>> diff --git a/arch/parisc/kernel/module.c b/arch/parisc/kernel/module.c
>> index ac5f34993b53..1c50093e2ebe 100644
>> --- a/arch/parisc/kernel/module.c
>> +++ b/arch/parisc/kernel/module.c
>> @@ -43,6 +43,7 @@
>>  #include <linux/elf.h>
>>  #include <linux/vmalloc.h>
>>  #include <linux/fs.h>
>> +#include <linux/ftrace.h>
>>  #include <linux/string.h>
>>  #include <linux/kernel.h>
>>  #include <linux/bug.h>
>> @@ -862,7 +863,7 @@ int module_finalize(const Elf_Ehdr *hdr,
>>  	const char *strtab = NULL;
>>  	const Elf_Shdr *s;
>>  	char *secstrings;
>> -	int err, symindex = -1;
>> +	int symindex = -1;
>>  	Elf_Sym *newptr, *oldptr;
>>  	Elf_Shdr *symhdr = NULL;
>>  #ifdef DEBUG
>> @@ -946,11 +947,13 @@ int module_finalize(const Elf_Ehdr *hdr,
>>  			/* patch .altinstructions */
>>  			apply_alternatives(aseg, aseg + s->sh_size, me->name);
>>
>> +#ifdef CONFIG_DYNAMIC_FTRACE
>>  		/* For 32 bit kernels we're compiling modules with
>>  		 * -ffunction-sections so we must relocate the addresses in the
>> -		 *__mcount_loc section.
>> +		 *  ftrace callsite section.
>>  		 */
>> -		if (symindex != -1 && !strcmp(secname, "__mcount_loc")) {
>> +		if (symindex != -1 && !strcmp(secname, FTRACE_CALLSITE_SECTION)) {
>> +			int err;
>>  			if (s->sh_type == SHT_REL)
>>  				err = apply_relocate((Elf_Shdr *)sechdrs,
>>  							strtab, symindex,
>> @@ -962,6 +965,7 @@ int module_finalize(const Elf_Ehdr *hdr,
>>  			if (err)
>>  				return err;
>>  		}
>> +#endif
>>  	}
>>  	return 0;
>>  }
>> diff --git a/arch/parisc/kernel/module.lds b/arch/parisc/kernel/module.lds
>> deleted file mode 100644
>> index 1a9a92aca5c8..000000000000
>> --- a/arch/parisc/kernel/module.lds
>> +++ /dev/null
>> @@ -1,7 +0,0 @@
>> -/* SPDX-License-Identifier: GPL-2.0 */
>> -
>> -SECTIONS {
>> -	__mcount_loc : {
>> -		*(__patchable_function_entries)
>> -	}
>> -}
>> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
>> index 9867d90d635e..9141f2263286 100644
>> --- a/include/linux/ftrace.h
>> +++ b/include/linux/ftrace.h
>> @@ -738,6 +738,11 @@ static inline unsigned long get_lock_parent_ip(void)
>>
>>  #ifdef CONFIG_FTRACE_MCOUNT_RECORD
>>  extern void ftrace_init(void);
>> +#ifdef CC_USING_PATCHABLE_FUNCTION_ENTRY
>> +#define FTRACE_CALLSITE_SECTION	"__patchable_function_entries"
>> +#else
>> +#define FTRACE_CALLSITE_SECTION	"__mcount_loc"
>> +#endif
>>  #else
>>  static inline void ftrace_init(void) { }
>>  #endif
>> diff --git a/kernel/module.c b/kernel/module.c
>> index ff2d7359a418..acf7962936c4 100644
>> --- a/kernel/module.c
>> +++ b/kernel/module.c
>> @@ -3222,7 +3222,7 @@ static int find_module_sections(struct module *mod, struct load_info *info)
>>  #endif
>>  #ifdef CONFIG_FTRACE_MCOUNT_RECORD
>>  	/* sechdrs[0].sh_size is always zero */
>> -	mod->ftrace_callsites = section_objs(info, "__mcount_loc",
>> +	mod->ftrace_callsites = section_objs(info, FTRACE_CALLSITE_SECTION,
>>  					     sizeof(*mod->ftrace_callsites),
>>  					     &mod->num_ftrace_callsites);
>>  #endif
>> --
>> 2.11.0
>>