[gdb/testsuite] Add KFAILs in gdb.base/longjmp.exp

Add KFAILs in test-case gdb.base/longjmp.exp for PR gdb/26967, covering
various ways that gdb is unable to recover the longjmp target if the libc
probe is not supported.

Tested on x86_64-linux.

Approved-By: Simon Marchi <simon.marchi@efficios.com>

gdb/testsuite/gdb.base/longjmp.exp

@@ -31,6 +31,43 @@ if {![runto_main]} {
    return 0
 }
 
+# With a libc with probes, all tests should pass.
+#
+# Without probes, we can still set a break on longjmp, but getting the longjmp
+# target may not work, in the following cases:
+# - gdbarch_get_longjmp_target_p (gdbarch) == 0: not implemented.
+# - gdbarch_get_longjmp_target (gdbarch) == 0: for instance on amd64 if
+#   tdep->jb_pc_offset == -1.
+# - gdbarch_get_longjmp_target (gdbarch) != 0: if we have a glibc with
+#   pointer mangling ( https://sourceware.org/glibc/wiki/PointerEncryption )
+#   then we retrieve a mangled longjmp target that needs to be demangled.
+#   For instance on amd64 with target board unix/-m32.
+#
+# Pointer demangling is currently not implemented for any target.
+# For the amd64 case, this would require copying for instance this:
+#   48 c1 ca 11             ror    $0x11,%rdx
+#   64 48 33 14 25 30 00    xor    %fs:0x30,%rdx
+# into a scratch space, save the register set, set %rdx to the mangled
+# longjmp target, displaced-step through the two insn and read the
+# demangled longjmp target from %rdx, and restore the register set.
+#
+# The failure mode in the first two cases is that the next degrades into a
+# continue.  The failure mode in the latter case is a failure to set a
+# breakpoint (matched by re_cannot_insert_bp) and a stop in longjmp.
+#
+# We detect the different failure modes and kfail these.
+
+set have_longjmp_probe 0
+gdb_test_multiple "info probes stap libc ^longjmp$" "" {
+    -re -wrap "No probes matched\\." {
+	pass $gdb_test_name
+    }
+    -re -wrap "\r\nstap\[ \t\]+libc\[ \t\]+longjmp\[ \t\]+.*" {
+	pass $gdb_test_name
+	set have_longjmp_probe 1
+    }
+}
+
 set bp_miss_step_1 [gdb_get_line_number "miss_step_1"]
 set bp_miss_step_2 [gdb_get_line_number "miss_step_2"]
 
@@ -38,6 +75,12 @@ set bp_start_test_1 [gdb_get_line_number "patt1"]
 set bp_start_test_2 [gdb_get_line_number "patt2"]
 set bp_start_test_3 [gdb_get_line_number "patt3"]
 
+set re_cannot_insert_bp \
+    [multi_line \
+	 "Warning:" \
+	 "Cannot insert breakpoint $decimal\\." \
+	 "Cannot access memory at address $hex"]
+
 #
 # Pattern 1 - simple longjmp.
 #
@@ -69,7 +112,18 @@ with_test_prefix "pattern 1" {
 	    gdb_test "next" "miss_step_1.*" "next into safety net"
 	}
 	-re "miss_step_1.*$gdb_prompt $" {
-	    fail $msg
+	    if { $have_longjmp_probe } {
+		fail $gdb_test_name
+	    } else {
+		kfail $gdb_test_name "gdb/26967"
+	    }
+	}
+	-re -wrap "\r\n$re_cannot_insert_bp\r\n.*" {
+	    if { $have_longjmp_probe } {
+		fail $gdb_test_name
+	    } else {
+		kfail $gdb_test_name "gdb/26967"
+	    }
 	}
     }
 }
@@ -105,7 +159,18 @@ with_test_prefix "pattern 2" {
 	    gdb_test "next" "miss_step_2.*" "next into safety net"
 	}
 	-re "miss_step_2.*$gdb_prompt $" {
-	    fail $msg
+	    if { $have_longjmp_probe } {
+		fail $gdb_test_name
+	    } else {
+		kfail $gdb_test_name "gdb/26967"
+	    }
+	}
+	-re -wrap "\r\n$re_cannot_insert_bp\r\n.*" {
+	    if { $have_longjmp_probe } {
+		fail $gdb_test_name
+	    } else {
+		kfail $gdb_test_name "gdb/26967"
+	    }
 	}
     }
 }
@@ -125,5 +190,16 @@ with_test_prefix "pattern 3" {
 	gdb_test "continue" "patt3.*" "continue to breakpoint at pattern start"
     }
 
-    gdb_test "next" "longjmp caught.*" "next over pattern"
+    gdb_test_multiple "next" "next over pattern" {
+	-re -wrap "longjmp caught.*" {
+	    pass $gdb_test_name
+	}
+	-re -wrap "\r\n$re_cannot_insert_bp\r\n.*" {
+	    if { $have_longjmp_probe } {
+		fail $gdb_test_name
+	    } else {
+		kfail $gdb_test_name "gdb/26967"
+	    }
+	}
+    }
 }