linux-kernel - Re: [PATCH] s390/perf: fix 'start' address of module's map

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Date:	Wed, 20 Jul 2016 13:51:27 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Song Shan Gong <gongss@...ux.vnet.ibm.com>
Cc:	acme@...nel.org, jolsa@...nel.org, borntraeger@...ibm.com,
	dsahern@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] s390/perf: fix 'start' address of module's map

On Tue, Jul 19, 2016 at 07:31:58PM +0800, Song Shan Gong wrote:
> At preset, when creating module's map, perf gets 'start' address by parsing
> '/proc/modules', but it's module base address, isn't the start address of
> '.text' section. In most archs, it's OK. But for s390, it places 'GOT' and
> 'PLT' relocations before '.text' section. So there exists an offset between
> module base address and '.text' section, which will incur wrong symbol
> resolution for modules.
> 
> Fix this bug by getting 'start' address of module's map from parsing
> '/sys/module/[module name]/sections/.text', not from '/proc/modules'.
> 
> Signed-off-by: Song Shan Gong <gongss@...ux.vnet.ibm.com>
> ---
>  tools/perf/arch/s390/util/Build          |  2 ++
>  tools/perf/arch/s390/util/sym-handling.c | 19 +++++++++++++++++++
>  tools/perf/util/machine.c                |  8 ++++++++
>  tools/perf/util/machine.h                |  1 +
>  4 files changed, 30 insertions(+)
>  create mode 100644 tools/perf/arch/s390/util/sym-handling.c
> 
> diff --git a/tools/perf/arch/s390/util/Build b/tools/perf/arch/s390/util/Build
> index 8a61372..5e322ed 100644
> --- a/tools/perf/arch/s390/util/Build
> +++ b/tools/perf/arch/s390/util/Build
> @@ -2,3 +2,5 @@ libperf-y += header.o
>  libperf-y += kvm-stat.o
>  
>  libperf-$(CONFIG_DWARF) += dwarf-regs.o
> +
> +libperf-y += sym-handling.o
> diff --git a/tools/perf/arch/s390/util/sym-handling.c b/tools/perf/arch/s390/util/sym-handling.c
> new file mode 100644
> index 0000000..ebfc55d
> --- /dev/null
> +++ b/tools/perf/arch/s390/util/sym-handling.c

I wonder we should rather put this into arch/s390/util/machine.c

other than that:

Acked-by: Jiri Olsa <jolsa@...nel.org>

thanks,
jirka

> @@ -0,0 +1,19 @@
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <unistd.h>
> +#include "util.h"
> +#include "machine.h"
> +#include "api/fs/fs.h"
> +
> +int arch__fix_module_text_start(u64 *start, const char *name)
> +{
> +	char path[PATH_MAX];
> +
> +	snprintf(path, PATH_MAX, "module/%.*s/sections/.text",
> +				(int)strlen(name) - 2, name + 1);
> +
> +	if (sysfs__read_ull(path, (unsigned long long *)start) < 0)
> +		return -1;
> +
> +	return 0;
> +}
> diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
> index b177218..97cc9f0 100644
> --- a/tools/perf/util/machine.c
> +++ b/tools/perf/util/machine.c
> @@ -1091,12 +1091,20 @@ static int machine__set_modules_path(struct machine *machine)
>  
>  	return map_groups__set_modules_path_dir(&machine->kmaps, modules_path, 0);
>  }
> +int __weak arch__fix_module_text_start(u64 *start __maybe_unused,
> +				const char *name __maybe_unused)
> +{
> +	return 0;
> +}
>  
>  static int machine__create_module(void *arg, const char *name, u64 start)
>  {
>  	struct machine *machine = arg;
>  	struct map *map;
>  
> +	if (arch__fix_module_text_start(&start, name) < 0)
> +		return -1;
> +
>  	map = machine__findnew_module_map(machine, start, name);
>  	if (map == NULL)
>  		return -1;
> diff --git a/tools/perf/util/machine.h b/tools/perf/util/machine.h
> index 41ac9cf..20739f7 100644
> --- a/tools/perf/util/machine.h
> +++ b/tools/perf/util/machine.h
> @@ -216,6 +216,7 @@ struct symbol *machine__find_kernel_function_by_name(struct machine *machine,
>  
>  struct map *machine__findnew_module_map(struct machine *machine, u64 start,
>  					const char *filename);
> +int arch__fix_module_text_start(u64 *start, const char *name);
>  
>  int __machine__load_kallsyms(struct machine *machine, const char *filename,
>  			     enum map_type type, bool no_kcore, symbol_filter_t filter);
> -- 
> 2.3.0
>