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

Felix Willgerodt via Gdb-patches
2023-07-18T11:58:55Z

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