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

[Songshan Gong <gongss@linux.vnet.ibm.com>]

在 7/27/2016 4:29 AM, Arnaldo Carvalho de Melo 写道:
> Em Tue, Jul 26, 2016 at 10:14:18PM +0200, Christian Borntraeger escreveu:
>> On 07/26/2016 09:50 PM, Arnaldo Carvalho de Melo wrote:
>>> Em Thu, Jul 21, 2016 at 11:10:51AM +0800, Song Shan Gong escreveu:
>>>> 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.
>>>
>>> I'll apply this as it fixes the problem for you and we need to get fixes
>>> in ASAP to get this into 4.8, but why can't we just use your method for
>>> all arches and get rid of this arch__ hook? I.e. if I look here in my
>>> x86_64 notebook I see:
>>>
>>> [acme@jouet linux]$ cat /sys/module/tun/sections/.text
>>> 0xffffffffc0af2000
>>> [acme@jouet linux]$ grep tun /proc/modules
>>> tun 28672 4 vhost_net, Live 0xffffffffc0af2000
>>> [acme@jouet linux]$
>>>
>>> So I could as well use what is in /sys/module/tun/sections/.text instead
>>> of reading it from /proc/modules and, in s390, reading it from
>>> /sys/module/tun/sections/.text.
>>>
>>> Do you see any problem with using this approach for _all_ arches?
>>
>> I think it should work well for _all_ arches but it will probably be
>> hard to test this without help.
>
> Well, we could check for the cases we don't know, i.e. read from both
> and warn about cases where it is different, except for s390 where we now
> which is the right one to pick.

Good idea!

>
>> I wouldn't be surprised if other architectures than s390 actually have
>> the same issue, so doing this for everybody might atually fix this somewhere
>> else.
>
> Would be nice to get info from other arch people, Michael, how this goes
> on ppc?
>
> - Arnaldo
>
>>>
>>> - Arnaldo
>>>
>>>> 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@linux.vnet.ibm.com>
>>>> Acked-by: Jiri Olsa <jolsa@kernel.org>
>>>> ---
>>>>  tools/perf/arch/s390/util/Build     |  2 ++
>>>>  tools/perf/arch/s390/util/machine.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/machine.c
>>>>
>>>> diff --git a/tools/perf/arch/s390/util/Build b/tools/perf/arch/s390/util/Build
>>>> index 8a61372..5bd7b92 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 += machine.o
>>>> diff --git a/tools/perf/arch/s390/util/machine.c b/tools/perf/arch/s390/util/machine.c
>>>> new file mode 100644
>>>> index 0000000..b9a95a1
>>>> --- /dev/null
>>>> +++ b/tools/perf/arch/s390/util/machine.c
>>>> @@ -0,0 +1,19 @@
>>>> +#include <unistd.h>
>>>> +#include <stdio.h>
>>>> +#include <string.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
>>>
>

-- 
SongShan Gong