[binutils-gdb] btrace, linux: use data_size and data_offset

[Markus Metzger <mmetzger at sourceware dot org>]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=010a18a1b12ec6d5219b7e602aa6abe12344dd1a

commit 010a18a1b12ec6d5219b7e602aa6abe12344dd1a
Author: Markus Metzger <markus.t.metzger@intel.com>
Date:   Mon Nov 17 11:18:05 2014 +0100

    btrace, linux: use data_size and data_offset
    
    In struct perf_event_mmap_page there are new fields data_size and data_offset
    that give the location of the perf_event data buffer relative to the mmap
    page.  Use them if they are present.
    
    gdb/
    	* nat/linux-btrace.c (linux_enable_bts): Check for
    	PERF_ATTR_SIZE_VER5.
    	Check for data_offset and data_size fields.  Use them.

Diff:
---
 gdb/ChangeLog          |  6 ++++++
 gdb/nat/linux-btrace.c | 21 ++++++++++++++++-----
 2 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 4c96e8a..a4cce4d 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,11 @@
 2015-07-02  Markus Metzger  <markus.t.metzger@intel.com>
 
+	* nat/linux-btrace.c (linux_enable_bts): Check for
+	PERF_ATTR_SIZE_VER5.
+	Check for data_offset and data_size fields.  Use them.
+
+2015-07-02  Markus Metzger  <markus.t.metzger@intel.com>
+
 	* NEWS: Announce new commands "record btrace pt" and "record pt".
 	Announce new options "set|show record btrace pt buffer-size".
 	* btrace.c: Include "rsp-low.h".
diff --git a/gdb/nat/linux-btrace.c b/gdb/nat/linux-btrace.c
index ddd79a3..3b630f5 100644
--- a/gdb/nat/linux-btrace.c
+++ b/gdb/nat/linux-btrace.c
@@ -642,7 +642,7 @@ linux_enable_bts (ptid_t ptid, const struct btrace_config_bts *conf)
   struct perf_event_mmap_page *header;
   struct btrace_target_info *tinfo;
   struct btrace_tinfo_bts *bts;
-  unsigned long long size, pages;
+  unsigned long long size, pages, data_offset, data_size;
   int pid, pg;
 
   tinfo = xzalloc (sizeof (*tinfo));
@@ -704,16 +704,27 @@ linux_enable_bts (ptid_t ptid, const struct btrace_config_bts *conf)
 	break;
     }
 
-  if (header == MAP_FAILED)
+  if (pages == 0)
     goto err_file;
 
+  data_offset = PAGE_SIZE;
+  data_size = size;
+
+#if defined (PERF_ATTR_SIZE_VER5)
+  if (offsetof (struct perf_event_mmap_page, data_size) <= header->size)
+    {
+      data_offset = header->data_offset;
+      data_size = header->data_size;
+    }
+#endif /* defined (PERF_ATTR_SIZE_VER5) */
+
   bts->header = header;
-  bts->bts.mem = ((const uint8_t *) header) + PAGE_SIZE;
-  bts->bts.size = size;
+  bts->bts.mem = ((const uint8_t *) header) + data_offset;
+  bts->bts.size = data_size;
   bts->bts.data_head = &header->data_head;
   bts->bts.last_head = 0;
 
-  tinfo->conf.bts.size = size;
+  tinfo->conf.bts.size = data_size;
   return tinfo;
 
  err_file: