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

[Mark Rutland]

Hi Jessica, Helge,

Are you ok with the module and parisc changes, repectively?

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@xxxxxxx>
> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> Cc: Helge Deller <deller@xxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: James E.J. Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
> Cc: Jessica Yu <jeyu@xxxxxxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Cc: Sven Schnelle <svens@xxxxxxxxxxxxxx>
> Cc: linux-parisc@xxxxxxxxxxxxxxx
> ---
>  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
>