Re: [PATCH v2] pahole: Add --kabi_prefix flag

[Shuyi Cheng <chengshuyi@linux.alibaba.com>]

On 5/20/21 4:07 AM, Jiri Olsa wrote:
> On Wed, May 19, 2021 at 10:44:44AM +0800, Shuyi Cheng wrote:
>> To solve problems similar to _RH_KABI_REPLACE. The _RH_KABI_REPLACE(_orig,
>> _new) macros perserve size alignment and kabi agreement between _orig and
>> _new.Below is the definition of this macro:
>>
>> # define _RH_KABI_REPLACE(_orig, _new)            \
>>      union {                        \
>>          _new;                    \
>>          struct {                \
>>              _orig;                \
>>          } __UNIQUE_ID(rh_kabi_hide);        \
>>          __RH_KABI_CHECK_SIZE_ALIGN(_orig, _new);    \
>>      }
> 
> hi,
> that macro sounds familiar ;-) I think this should be already
> solved directly in the header file by this one:
> 
>    https://gitlab.com/cki-project/kernel-ark/-/commit/331be9c5a436057ee852075c102d9d90a9046a30
> 
> jirka
> 

Well, this patch solves this problem very well from the kernel level. 
But there are many mirrors [here](http://debuginfo.centos.org/7/x86_64/) 
that still have this problem. And these mirrors support ebpf, so it is 
very important to effectively extract the btf segment from these 
mirrors. :-)

>>
>>
>> __UNIQUE_ID uses the __COUNTER__ macro, and the __COUNTER__ macro is
>> automatically incremented by 1 every time it is precompiled. Therefore, in
>> different compilation units, the same structure has different names.Here is
>> a concrete example:
>>
>> struct acpi_dev_node {
>>      union {
>>          struct acpi_device *companion;
>>          struct {
>>              void *handle;
>>          } __UNIQUE_ID_rh_kabi_hide29;
>>          union {        };
>>      };
>> };
>> struct acpi_dev_node {
>>      union {
>>          struct acpi_device *companion;
>>          struct {
>>              void *handle;
>>          } __UNIQUE_ID_rh_kabi_hide31;
>>          union {        };
>>      };
>> };
>>
>> Finally, it will cause the btf algorithm to de-duplication efficiency is not
>> high, and time-consuming. For example, running ./pahole -J
>> vmlinux-3.10.0-1160.el7.x86_64 without --kabi_prefix flag, the running time
>> is:
>>                  real 8m28.912s
>>                  user 8m27.271s
>>                  sys 0m1.471s
>> And the size of the generated btf segment is 30678240 bytes.
>>
>> After adding the patch, running ./pahole
>> --kabi_prefix=__UNIQUE_ID_rh_kabi_hide -J vmlinux-3.10.0-1160.el7.x86_64.
>> The running time of the command is:
>>                  real 0m19.634s
>>                  user 0m18.457s
>>                  sys 0m1.169s
>> And the size of the generated btf segment is 3117719 bytes.
>>
>> ---
>>
>> v1:https://lore.kernel.org/dwarves/CAEf4Bzazh4RNCY3rGRRXfO2wJ7DSiMx8w+61B_hjhu9FrOffpQ@mail.gmail.com
>> v1->v2:
>> --Change btf_prefix to --kabi_prefix.
>> --Add man page.
>> --Add space after if and comma.
>>
>>   man-pages/pahole.1 |  4 ++++
>>   pahole.c           | 10 ++++++++++
>>   pahole_strings.h   |  2 ++
>>   strings.c          |  9 ++++++++-
>>   4 files changed, 24 insertions(+), 1 deletion(-)
>>
>> diff --git a/man-pages/pahole.1 b/man-pages/pahole.1
>> index a10738f..2659fe6 100644
>> --- a/man-pages/pahole.1
>> +++ b/man-pages/pahole.1
>> @@ -340,6 +340,10 @@ Show a traditional string version, i.e.: "v1.18".
>>   Show a numeric only version, suitable for use in Makefiles and scripts
>> where
>>   one wants to know what if the installed version has some feature, i.e.: 118
>> instead of "v1.18".
>>
>> +.TP
>> +.B \-\-kabi_prefix=STRING
>> +When the prefix of the string is STRING, treat the string as STRING.
>> +
>>   .SH NOTES
>>
>>   To enable the generation of debugging information in the Linux kernel build
>> diff --git a/pahole.c b/pahole.c
>> index dc40ccf..6a700d9 100644
>> --- a/pahole.c
>> +++ b/pahole.c
>> @@ -24,6 +24,7 @@
>>   #include "btf_encoder.h"
>>   #include "libbtf.h"
>>   #include "lib/bpf/src/libbpf.h"
>> +#include "pahole_strings.h"
>>
>>   static bool btf_encode;
>>   static bool ctf_encode;
>> @@ -855,6 +856,7 @@ ARGP_PROGRAM_VERSION_HOOK_DEF = dwarves_print_version;
>>   #define ARGP_btf_gen_floats	   322
>>   #define ARGP_btf_gen_all	   323
>>   #define ARGP_with_flexible_array   324
>> +#define ARGP_kabi_prefix   325
>>
>>   static const struct argp_option pahole__options[] = {
>>   	{
>> @@ -1140,6 +1142,12 @@ static const struct argp_option pahole__options[] = {
>>   		.doc  = "Path to the base BTF file",
>>   	},
>>   	{
>> +		.name = "kabi_prefix",
>> +		.key = ARGP_kabi_prefix,
>> +		.arg = "STRING",
>> +		.doc = "When the prefix of the string is STRING, treat the string as
>> STRING.",
>> +	},
>> +	{
>>   		.name = "btf_encode",
>>   		.key  = 'J',
>>   		.doc  = "Encode as BTF",
>> @@ -1297,6 +1305,8 @@ static error_t pahole__options_parser(int key, char
>> *arg,
>>   		btf_encode_force = true;		break;
>>   	case ARGP_btf_base:
>>   		base_btf_file = arg;			break;
>> +	case ARGP_kabi_prefix:
>> +		kabi_prefix = arg;		break;
>>   	case ARGP_numeric_version:
>>   		print_numeric_version = true;		break;
>>   	case ARGP_btf_gen_floats:
>> diff --git a/pahole_strings.h b/pahole_strings.h
>> index 522fbf2..a836ba8 100644
>> --- a/pahole_strings.h
>> +++ b/pahole_strings.h
>> @@ -14,6 +14,8 @@ struct strings {
>>   	struct btf *btf;
>>   };
>>
>> +extern const char *kabi_prefix;
>> +
>>   struct strings *strings__new(void);
>>
>>   void strings__delete(struct strings *strings);
>> diff --git a/strings.c b/strings.c
>> index d37f49d..d1a54ec 100644
>> --- a/strings.c
>> +++ b/strings.c
>> @@ -17,6 +17,8 @@
>>   #include "dutil.h"
>>   #include "lib/bpf/src/libbpf.h"
>>
>> +const char *kabi_prefix;
>> +
>>   struct strings *strings__new(void)
>>   {
>>   	struct strings *strs = malloc(sizeof(*strs));
>> @@ -48,7 +50,12 @@ strings_t strings__add(struct strings *strs, const char
>> *str)
>>   	if (str == NULL)
>>   		return 0;
>>
>> -	index = btf__add_str(strs->btf, str);
>> +	if (kabi_prefix &&
>> +		strncmp(str, kabi_prefix, strlen(kabi_prefix)) == 0)
>> +		index = btf__add_str(strs->btf, kabi_prefix);
>> +	else
>> +		index = btf__add_str(strs->btf, str);
>> +		
>>   	if (index < 0)
>>   		return 0;
>>
>> -- 
>> 1.8.3.1
>>