[PATCH v3] pahole: Add --kabi_prefix flag

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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);    \
    }


__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.

Acked-by: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <arnaldo.melo@xxxxxxxxx>
Cc: Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx>
Cc: Wenan Mao <wenan.mao@xxxxxxxxxxxxxxxxx>
Signed-off-by: Shuyi Cheng <chengshuyi@xxxxxxxxxxxxxxxxx>
---

v1: https://lore.kernel.org/dwarves/a249699a-7c6c-4d4a-71b0-87981c8d229e@xxxxxxxxxxxxxxxxx/
v1->v2:
-- Change btf_prefix to --kabi_prefix.
-- Add man page.
-- Add space after if and comma.

v2: https://lore.kernel.org/dwarves/ec80d351-ac2f-5c48-c339-c2c503d36d68@xxxxxxxxxxxxxxxxx/
v2->v3:
-- Keep the '=' indentation.
-- Remove extra whitespace.

 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..f2406e4 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..d5eb3a1 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





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