[gdb/testsuite] Add xfail in gdb.python/py-record-btrace.exp

There's a HW bug affecting Processor Trace on some Intel processors
(Ice Lake to Raptor Lake microarchitectures).

The bug was exposed by linux kernel commit 670638477aed
("perf/x86/intel/pt: Opportunistically use single range output mode"),
added in version v5.5.0, and was worked around by commit ce0d998be927
("perf/x86/intel/pt: Fix sampling using single range output") in version
6.1.0.

The bug manifests (on a Performance-core of an i7-1250U, an Alder Lake cpu) in
a single test-case:
...
(gdb) python insn = r.instruction_history^M
warning: Decode error (-20) at instruction 33 (offset = 0x3d6a, \
  pc = 0x400501): compressed return without call.^M
(gdb) FAIL: gdb.python/py-record-btrace.exp: prepare record: \
  python insn = r.instruction_history
...

Add a corresponding XFAIL.

Note that the i7-1250U has both Performance-cores and Efficient-cores, and on
an Efficient-Core the test-case runs without any problems, so if the testsuite
run is not pinned to a specific cpu, the test may either PASS or XFAIL.

Tested on x86_64-linux:
- openSUSE Leap 15.4 with linux kernel version 5.14.21
- openSUSE Tumbleweed with linux kernel version 6.1.8

PR testsuite/30075
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30075

diff --git a/gdb/testsuite/gdb.python/py-record-btrace.exp b/gdb/testsuite/gdb.python/py-record-btrace.exp
index 555b70ae336df072d7c363cfbf28be7efce86421..c055a882f859b62e19b202115dff2a81f22a340b 100644 (file)
--- a/gdb/testsuite/gdb.python/py-record-btrace.exp
+++ b/gdb/testsuite/gdb.python/py-record-btrace.exp
@@ -54,7 +54,48 @@ with_test_prefix "prepare record" {
     gdb_test "python print(r.method)" "btrace"
     gdb_test "python print(r.format)" "pt|bts"
     gdb_test "stepi 100" ".*"
-    gdb_test_no_output "python insn = r.instruction_history"
+
+    # There's a HW bug affecting Processor Trace on some Intel processors.
+    # The bug was exposed by linux kernel commit 670638477aed
+    # ("perf/x86/intel/pt: Opportunistically use single range output mode"),
+    # added in version v5.5.0, and was worked around by commit ce0d998be927
+    # ("perf/x86/intel/pt: Fix sampling using single range output") in version
+    # 6.1.0.  Detect the kernel version range for which the problem may
+    # manifest.
+    set have_xfail 0
+    set v [linux_kernel_version]
+    if { $v != {} } {
+       set have_xfail \
+           [expr [version_compare [list 5 5 0] <= $v] \
+                && [version_compare $v < [list 6 1 0]]]
+    }
+    set nonl_re \[^\r\n\]
+    set xfail_re \
+       [join \
+            [list \
+                 "warning: Decode error \\($nonl_re*\\) at instruction $decimal" \
+                 "\\(offset = $hex, pc = $hex\\):" \
+                 "$nonl_re*\\."]]
+
+    set got_xfail 0
+    set cmd "python insn = r.instruction_history"
+    gdb_test_multiple $cmd "" {
+       -re "^[string_to_regexp $cmd]\r\n$::gdb_prompt $" {
+           pass $gdb_test_name
+       }
+       -re -wrap "$xfail_re" {
+           if { $have_xfail } {
+               xfail $gdb_test_name
+               set got_xfail 1
+           } else {
+               fail $gdb_test_name
+           }
+       }
+    }
+    if { $got_xfail } {
+       return
+    }
+
     gdb_test_no_output "python call = r.function_call_history"
     gdb_test_no_output "python i = insn\[0\]"
     gdb_test_no_output "python c = call\[0\]"