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

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Date:	Tue, 19 Jul 2016 09:50:43 +0800
From:	Songshan Gong <gongss@...ux.vnet.ibm.com>
To:	Jiri Olsa <jolsa@...hat.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



在 7/19/2016 9:37 AM, Songshan Gong 写道:
>
>
> 在 7/18/2016 10:07 PM, Jiri Olsa 写道:
>> 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..
>
> Oh, yes.
>
Sorry, just ignore the upper reply.

I use the 'module_name' here instead of 'name', because 'name' is 
something like '[module_name]', I need strip the '[' and ']', so I have 
to set the tail ']' to '\0' to indicate the string end, which will need 
change the constant variable 'name'.


>
>>> +
>>> +    if (sysfs__read_ull(path, (unsigned long long *)start) < 0) {
>>> +        free(module_name);
>>> +        return -1;
>>> +    }
>>
>> leaking module_name in here
>
> yes, thanks.
>>
>>> +    return 0;
>>> +}
>>
>> SNIP
>>
>> thanks,
>> jirka
>>
>

-- 
SongShan Gong