[PATCH 5/8] Step over fork/vfork syscall insn in gdbserver

[Yao Qi <qiyaoltc@gmail.com>]

We can also extend disp-step-syscall.exp to test GDBserver step over
breakpoint on syscall instruction.  That is, we set a breakpoint
with a false condition on syscall instruction, so that GDBserver will
step over it.

This test triggers a GDBserver internal error, which can be fixed by
this series.

(gdb) PASS: gdb.base/disp-step-syscall.exp: fork: break cond on target: break on syscall insns
continue^M
Continuing.^M
Remote connection closed^M
(gdb) FAIL: gdb.base/disp-step-syscall.exp: fork: break cond on target: continue to fork again

In GDBserver, there is an internal error,

/home/yao/SourceCode/gnu/gdb/git/gdb/gdbserver/linux-low.c:1922: A problem internal to GDBserver has been detected.
unsuspend LWP 25554, suspended=-1

the simplified reproducer is like,

$ ./gdb ./testsuite/outputs/gdb.base/disp-step-syscall/disp-step-fork
(gdb) b main
(gdb) c
(gdb) disassemble fork // in order to find the address of insn 'syscall'
....
   0x00007ffff7ad6023 <+179>:	syscall
(gdb) b *0x00007ffff7ad6023 if main == 0
(gdb) c

gdb/testsuite:

2016-02-19  Yao Qi  <yao.qi@linaro.org>

	* gdb.base/disp-step-fork.c (main): Increase loop boundary.
	* gdb.base/disp-step-vfork.c (main): Likewise.
	* gdb.base/disp-step-syscall.exp (disp_step_cross_syscall): Test
	breakpoint condition evaluated on the target side.
---
 gdb/testsuite/gdb.base/disp-step-fork.c      |  2 +-
 gdb/testsuite/gdb.base/disp-step-syscall.exp | 38 ++++++++++++++++++++++++++++
 gdb/testsuite/gdb.base/disp-step-vfork.c     |  2 +-
 3 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/gdb/testsuite/gdb.base/disp-step-fork.c b/gdb/testsuite/gdb.base/disp-step-fork.c
index d8d602f..6d477ea 100644
--- a/gdb/testsuite/gdb.base/disp-step-fork.c
+++ b/gdb/testsuite/gdb.base/disp-step-fork.c
@@ -26,7 +26,7 @@ main (void)
 {
   int i, pid;
 
-  for (i = 0; i < 4; i++)
+  for (i = 0; i < 6; i++)
     {
       pid = fork ();
       if (pid == 0) /* child */
diff --git a/gdb/testsuite/gdb.base/disp-step-syscall.exp b/gdb/testsuite/gdb.base/disp-step-syscall.exp
index 9e43fbb..53ac1e1 100644
--- a/gdb/testsuite/gdb.base/disp-step-syscall.exp
+++ b/gdb/testsuite/gdb.base/disp-step-syscall.exp
@@ -153,6 +153,44 @@ proc disp_step_cross_syscall { syscall } {
     }
 	}
 
+	with_test_prefix "break cond on target" {
+	    set cond_bp_target 1
+
+	    set test "set breakpoint condition-evaluation target"
+	    gdb_test_multiple $test $test {
+		-re "warning: Target does not support breakpoint condition evaluation.\r\nUsing host evaluation mode instead.\r\n$gdb_prompt $" {
+		    # Target doesn't support breakpoint condition
+		    # evaluation on its side.
+		    set cond_bp_target 0
+		}
+		-re "^$test\r\n$gdb_prompt $" {
+		}
+	    }
+
+	    if { $cond_bp_target } {
+		gdb_test "continue" "Continuing\\..*Breakpoint \[0-9\]+, (.* in |__libc_|)$syscall \\(\\).*" \
+		    "continue to $syscall"
+
+		# Create a breakpoint with the condition which is false.
+		set syscall_insn_bp 0
+		gdb_test_multiple "break \*$syscall_insn_addr if main == 0" \
+		    "break on syscall insns" {
+			-re "Breakpoint (\[0-9\]*) at .*$gdb_prompt $" {
+			    set syscall_insn_bp $expect_out(1,string)
+			    pass "break on syscall insns"
+			}
+		    }
+
+		gdb_test "continue" "Continuing\\..*Breakpoint \[0-9\]+, (.* in |__libc_|)$syscall \\(\\).*" \
+		    "continue to $syscall again"
+
+		# Delete breakpoint syscall insns to avoid interference to
+		# other syscalls.
+		gdb_test_no_output "delete $syscall_insn_bp" \
+		    "delete break $syscall insn"
+	    }
+	}
+
 	gdb_test_no_output "delete $syscall_bp" "delete break $syscall"
 
 	gdb_test "continue" "Continuing\\..*Breakpoint \[0-9\]+, marker \\(\\) at.*" \
diff --git a/gdb/testsuite/gdb.base/disp-step-vfork.c b/gdb/testsuite/gdb.base/disp-step-vfork.c
index 17bef55..35665ab 100644
--- a/gdb/testsuite/gdb.base/disp-step-vfork.c
+++ b/gdb/testsuite/gdb.base/disp-step-vfork.c
@@ -25,7 +25,7 @@ main (void)
 {
   int i, pid;
 
-  for (i = 0; i < 4; i++)
+  for (i = 0; i < 6; i++)
     {
       pid = vfork ();
       if (pid == -1)
-- 
1.9.1