linux-kernel - Re: [RFC PATCH V2] s390/perf: fix 'start' address of module's map

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Date:	Mon, 18 Jul 2016 16:07:54 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Song Shan Gong <gongss@...ux.vnet.ibm.com>
Cc:	acme@...nel.org, jolsa@...nel.org, dsahern@...il.com,
	linux-kernel@...r.kernel.org, borntraeger@...ibm.com
Subject: Re: [RFC PATCH V2] s390/perf: fix 'start' address of module's map

On Fri, Jul 15, 2016 at 06:15:11PM +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 | 27 +++++++++++++++++++++++++++
>  tools/perf/util/machine.c                |  8 ++++++++
>  tools/perf/util/machine.h                |  1 +
>  4 files changed, 38 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..ff51336
> --- /dev/null
> +++ b/tools/perf/arch/s390/util/sym-handling.c
> @@ -0,0 +1,27 @@
> +#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];
> +	char *module_name = NULL;
> +	int len;
> +
> +	if (!(module_name = strdup(name)))
> +		return -1;
> +
> +	len = strlen(module_name);
> +	module_name[len - 1] = '\0';
> +	snprintf(path, PATH_MAX, "module/%s/sections/.text",
> +				module_name + 1);

why can't you use 'name' in here? I can't see the reason
you allocated module_name..

> +
> +	if (sysfs__read_ull(path, (unsigned long long *)start) < 0) {
> +		free(module_name);
> +		return -1;
> +	}

leaking module_name in here

> +	return 0;
> +}

SNIP

thanks,
jirka