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

[Jiri Olsa <jolsa@redhat.com>]

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

> 
> 
> __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
>