[PATCH v10 08/10] btrace, linux: Enable ptwrite packets.

[Felix Willgerodt <felix.willgerodt@intel.com>]

Enable ptwrite in the PT config, if it is supported by the kernel.
---
 gdb/nat/linux-btrace.c | 58 ++++++++++++++++++++++++++++++++++++++++++
 gdb/record-btrace.c    |  5 ++++
 2 files changed, 63 insertions(+)

diff --git a/gdb/nat/linux-btrace.c b/gdb/nat/linux-btrace.c
index c5b3f1c93cf..689f4c46dd4 100644
--- a/gdb/nat/linux-btrace.c
+++ b/gdb/nat/linux-btrace.c
@@ -417,6 +417,57 @@ cpu_supports_bts (void)
     }
 }
 
+/* Read config bits.  */
+
+static bool
+linux_read_pt_config_bit (const std::string &feature, uint64_t *config_bit)
+{
+  std::string filename
+      = "/sys/bus/event_source/devices/intel_pt/format/" + feature;
+  gdb_file_up file = gdb_fopen_cloexec (filename.c_str (), "r");
+
+  if (file.get () == nullptr || config_bit == nullptr)
+    return false;
+
+  int found = fscanf (file.get (), "config:%lu", config_bit);
+
+  if (found != 1)
+    {
+      warning (_("Failed to determine config bit from %s."),
+	       filename.c_str ());
+      return false;
+    }
+
+  return true;
+}
+
+
+/* Check whether the linux target supports Intel Processor Trace PTWRITE.  */
+
+static bool
+linux_supports_ptwrite (uint64_t *config_bit)
+{
+  static const char filename[]
+      = "/sys/bus/event_source/devices/intel_pt/caps/ptwrite";
+  gdb_file_up file = gdb_fopen_cloexec (filename, "r");
+
+  if (file.get () == nullptr)
+    return false;
+
+  int status, found = fscanf (file.get (), "%d", &status);
+
+  if (found != 1)
+    {
+      warning (_("Failed to determine ptwrite support from %s."), filename);
+      return false;
+    }
+
+  if (!linux_read_pt_config_bit ("ptw", config_bit))
+    return false;
+
+  return status == 1;
+}
+
 /* The perf_event_open syscall failed.  Try to print a helpful error
    message.  */
 
@@ -626,6 +677,13 @@ linux_enable_pt (ptid_t ptid, const struct btrace_config_pt *conf)
   pt->attr.exclude_hv = 1;
   pt->attr.exclude_idle = 1;
 
+  uint64_t config_bit;
+  if (conf->ptwrite && linux_supports_ptwrite (&config_bit))
+    {
+      pt->attr.config |= 1 << config_bit;
+      tinfo->conf.pt.ptwrite = conf->ptwrite;
+    }
+
   errno = 0;
   scoped_fd fd (syscall (SYS_perf_event_open, &pt->attr, pid, -1, -1, 0));
   if (fd.get () < 0)
diff --git a/gdb/record-btrace.c b/gdb/record-btrace.c
index c93b3d7c8de..ad3160d42c5 100644
--- a/gdb/record-btrace.c
+++ b/gdb/record-btrace.c
@@ -3295,4 +3295,9 @@ to see the actual buffer size."), NULL, show_record_pt_buffer_size_value,
 
   record_btrace_conf.bts.size = 64 * 1024;
   record_btrace_conf.pt.size = 16 * 1024;
+#if (LIBIPT_VERSION >= 0x200)
+  record_btrace_conf.pt.ptwrite = true;
+#else
+  record_btrace_conf.pt.ptwrite = false;
+#endif
 }
-- 
2.34.1

Intel Deutschland GmbH
Registered Address: Am Campeon 10, 85579 Neubiberg, Germany
Tel: +49 89 99 8853-0, www.intel.de <http://www.intel.de>
Managing Directors: Christin Eisenschmid, Sharon Heck, Tiffany Doon Silva  
Chairperson of the Supervisory Board: Nicole Lau
Registered Office: Munich
Commercial Register: Amtsgericht Muenchen HRB 186928