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

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Date:	Tue, 19 Jul 2016 11:35:13 +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 9:50 AM, Songshan Gong 写道:
>
>
> 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'.
>
eeee, I found a new way to implement it.

I could use '%.*s' to format the 'path', 'name' is enough indeed.

It's so concise now. Appreciate.
>
>>
>>>> +
>>>> +    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