[PATCH] btf: Add --btf_prefix flag

[程书意 <chengshuyi@linux.alibaba.com>]

To solve problems similar to _RH_KABI_REPLACE, _RH_KABI_REPLACE makes 
many structures have different names, resulting in a
particularly large vmlinux btf. For example, running ./pahole -J 
vmlinux-3.10.0-1160.el7.x86_64 without --btf_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 
--btf_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
The size of the generated btf segment is 3117719 bytes.

Thanks.

Signed-off-by: chengshuyi <chengshuyi@linux.alibaba.com>
---
  pahole.c         | 10 ++++++++++
  pahole_strings.h |  2 ++
  strings.c        |  9 +++++++--
  3 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/pahole.c b/pahole.c
index dc40ccf..0b4f4ca 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_btf_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 = "btf_prefix",
+        .key = ARGP_btf_prefix,
+        .arg = "STRING",
+        .doc = "Strings with the same prefix are considered the same.",
+    },
+    {
          .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_btf_prefix:
+        btf_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..bf3dc7c 100644
--- a/pahole_strings.h
+++ b/pahole_strings.h
@@ -14,6 +14,8 @@ struct strings {
      struct btf *btf;
  };

+extern const char *btf_prefix;
+
  struct strings *strings__new(void);

  void strings__delete(struct strings *strings);
diff --git a/strings.c b/strings.c
index d37f49d..911ce25 100644
--- a/strings.c
+++ b/strings.c
@@ -16,6 +16,9 @@

  #include "dutil.h"
  #include "lib/bpf/src/libbpf.h"
+#include "libbtf.h"
+
+const char *btf_prefix;

  struct strings *strings__new(void)
  {
@@ -47,8 +50,10 @@ strings_t strings__add(struct strings *strs, const 
char *str)

      if (str == NULL)
          return 0;
-
-    index = btf__add_str(strs->btf, str);
+    if(btf_prefix && strncmp(str,btf_prefix,strlen(btf_prefix))==0)
+        index = btf__add_str(strs->btf, btf_prefix);
+    else
+        index = btf__add_str(strs->btf, str);
      if (index < 0)
          return 0;

-- 
1.8.3.1