[binutils-gdb/gdb-7.10-branch] btrace: diagnose "record btrace pt" without libipt

[Markus Metzger <mmetzger at sourceware dot org>]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=bab694b7f968cc5703a69df694b5968384d6c0b4

commit bab694b7f968cc5703a69df694b5968384d6c0b4
Author: Markus Metzger <markus.t.metzger@intel.com>
Date:   Thu Nov 19 14:33:41 2015 +0100

    btrace: diagnose "record btrace pt" without libipt
    
    If GDB has been configured without libipt support, i.e. HAVE_LIBIPT is
    undefined, and is running on a system that supports Intel(R) Processor Trace,
    GDB will run into an internal error when trying to decode the trace.
    
        (gdb) record btrace
        (gdb) s
        usage (name=0x7fffffffe954 "fib-64")
            at src/fib.c:12
        12          fprintf(stderr, "usage: %s <num>\n", name);
        (gdb) info record
        Active record target: record-btrace
        Recording format: Intel(R) Processor Trace.
        Buffer size: 16kB.
        gdb/btrace.c:971: internal-error: Unexpected branch trace format.
        A problem internal to GDB has been detected,
        further debugging may prove unreliable.
        Quit this debugging session? (y or n)
    
    This requires a system with Linux kernel 4.1 or later running on a 5th
    Generation Intel Core processor or later.
    
    The issue is documented as PR 19297.
    
    When trying to enable branch tracing, in addition to checking the target
    support for the requested branch tracing format, also check whether GDB
    supports. it.
    
    gdb/
    	* btrace.c (btrace_enable): Check whether HAVE_LIBIPT is defined.

Diff:
---
 gdb/ChangeLog | 5 +++++
 gdb/btrace.c  | 5 +++++
 2 files changed, 10 insertions(+)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 94bcf9f..f2b395f 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2015-11-26  Markus Metzger  <markus.t.metzger@intel.com>
+
+	PR 19297
+	* btrace.c (btrace_enable): Check whether HAVE_LIBIPT is defined.
+
 2015-09-14  Peter Bergner  <bergner@vnet.ibm.com>
 
 	PR gdb/18957
diff --git a/gdb/btrace.c b/gdb/btrace.c
index 1618e55..ada0eb7 100644
--- a/gdb/btrace.c
+++ b/gdb/btrace.c
@@ -1020,6 +1020,11 @@ btrace_enable (struct thread_info *tp, const struct btrace_config *conf)
   if (tp->btrace.target != NULL)
     return;
 
+#if !defined (HAVE_LIBIPT)
+  if (conf->format == BTRACE_FORMAT_PT)
+    error (_("GDB does not support Intel(R) Processor Trace."));
+#endif /* !defined (HAVE_LIBIPT) */
+
   if (!target_supports_btrace (conf->format))
     error (_("Target does not support branch tracing."));