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

[Jiri Olsa <jolsa@redhat.com>]

On Thu, May 20, 2021 at 06:27:48PM +0800, Shuyi Cheng wrote:
> 
> 
> 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. :-)

hum, the link shows 3.10.* centos kernel, right?
AFAIK there's no BTF support in those kernels..

but maybe I'm missing some backporting channel,
could you please point me to related sources?

jirka

> 
> > > 
> > > 
> > > __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
> > > 
>