linux-kernel - Re: [PATCH] [RFC V1]s390/perf: fix 'start' address of module's map

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Date:	Fri, 8 Jul 2016 10:17:30 +0800
From:	Songshan Gong <gongss@...ux.vnet.ibm.com>
To:	acme@...nel.org, jolsa@...nel.org
Cc:	dsahern@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [RFC V1]s390/perf: fix 'start' address of module's map



在 7/7/2016 9:49 AM, Song Shan Gong 写道:
> 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 | 49 ++++++++++++++++++++++++++++++++
>  tools/perf/util/machine.c                |  6 ++++
>  tools/perf/util/machine.h                |  2 ++
>  4 files changed, 59 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..efe2a50
> --- /dev/null
> +++ b/tools/perf/arch/s390/util/sym-handling.c
> @@ -0,0 +1,49 @@
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <unistd.h>
> +#include "symbol.h"
> +#include "map.h"
> +#include "util.h"
> +#include "machine.h"
> +
> +int arch__fix_module_baseaddr(struct machine *machine,
> +		u64 *start, const char *name)
> +{
> +	char path[PATH_MAX];
> +	char *module_name = strdup(name);
> +	int len = strlen(module_name);
> +	FILE *file;
> +	int err = 0;
> +	u64 text_start;
> +	char *line = NULL;
> +	size_t n;
> +	char *sep;
> +
> +	module_name[len - 1] = '\0';
> +	module_name += 1;
> +	snprintf(path, PATH_MAX, "%s/sys/module/%s/sections/.text",
> +				machine->root_dir, module_name);
> +	file = fopen(path, "r");
> +	if (file == NULL)
> +		return -1;
> +
> +	len = getline(&line, &n, file);
> +	if (len < 0) {
> +		err = -1;
> +		goto out;
> +	}
> +	line[--len] = '\0'; /* \n */
> +	sep = strrchr(line, 'x');
> +	if (sep == NULL) {
> +		err = -1;
> +		goto out;
> +	}
> +	hex2u64(sep + 1, &text_start);
> +
> +	*start = text_start;
> +out:
> +	free(line);
> +	fclose(file);
> +	free(module_name - 1);
> +	return err;
> +}
> diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
> index b177218..e5c2721 100644
> --- a/tools/perf/util/machine.c
> +++ b/tools/perf/util/machine.c
> @@ -1091,12 +1091,18 @@ 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_baseaddr(struct machine *machine __maybe_unused,
> +				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;
>
> +	arch__fix_module_baseaddr(machine, &start, name);

As the description says, I would change the function name to 
'arch__fix_module_text_start';

>  	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..da7b6c0 100644
> --- a/tools/perf/util/machine.h
> +++ b/tools/perf/util/machine.h
> @@ -216,6 +216,8 @@ 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_baseaddr(struct machine *machine, 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);
>

-- 
SongShan Gong