[binutils-gdb] Step over fork/vfork syscall insn in gdbserver

[Yao Qi <qiyao at sourceware dot org>]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=92fa70b0bd8690d979357ebcdb501a9e4aa42ea6

commit 92fa70b0bd8690d979357ebcdb501a9e4aa42ea6
Author: Yao Qi <yao.qi@linaro.org>
Date:   Thu Mar 3 09:17:44 2016 +0000

    Step over fork/vfork syscall insn in gdbserver
    
    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:
    
    2016-03-03  Yao Qi  <yao.qi@linaro.org>
    
    	* gdb.base/disp-step-syscall.exp (break_cond_on_syscall): New.
    	If target supports condition evaluation on target, invoke
    	break_cond_on_syscall for fork and vfork.

Diff:
---
 gdb/testsuite/ChangeLog                      |  6 +++
 gdb/testsuite/gdb.base/disp-step-syscall.exp | 57 ++++++++++++++++++++++++++++
 2 files changed, 63 insertions(+)

diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 244efcc..eab1255 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,5 +1,11 @@
 2016-03-03  Yao Qi  <yao.qi@linaro.org>
 
+	* gdb.base/disp-step-syscall.exp (break_cond_on_syscall): New.
+	If target supports condition evaluation on target, invoke
+	break_cond_on_syscall for fork and vfork.
+
+2016-03-03  Yao Qi  <yao.qi@linaro.org>
+
 	* gdb.base/disp-step-syscall.exp: Don't invoke
 	support_displaced_stepping.
 	(disp_step_cross_syscall): Test with displaced stepping off and
diff --git a/gdb/testsuite/gdb.base/disp-step-syscall.exp b/gdb/testsuite/gdb.base/disp-step-syscall.exp
index 3cf436d..0aac649 100644
--- a/gdb/testsuite/gdb.base/disp-step-syscall.exp
+++ b/gdb/testsuite/gdb.base/disp-step-syscall.exp
@@ -168,5 +168,62 @@ proc disp_step_cross_syscall { syscall } {
     }
 }
 
+# Set a breakpoint with a condition that evals false on syscall
+# instruction.  In fact, it tests GDBserver steps over syscall
+# instruction.
+
+proc break_cond_on_syscall { syscall } {
+    with_test_prefix "break cond on target : $syscall" {
+	set testfile "disp-step-$syscall"
+
+	set ret [setup $syscall]
+
+	set syscall_insn_addr [lindex $ret 0]
+	set syscall_insn_next_addr [lindex $ret 1]
+	if { $syscall_insn_addr == -1 } {
+	    return -1
+	}
+
+	gdb_test "continue" "Continuing\\..*Breakpoint \[0-9\]+, (.* in |__libc_|)$syscall \\(\\).*" \
+	    "continue to $syscall"
+	# Delete breakpoint syscall insns to avoid interference with other syscalls.
+	delete_breakpoints
+
+
+	# Create a breakpoint with a condition that evals false.
+	gdb_test "break \*$syscall_insn_addr if main == 0" \
+	    "Breakpoint \[0-9\]* at .*"
+
+	gdb_test "break marker" "Breakpoint.*at.* file .*${testfile}.c, line.*"
+	gdb_test "continue" "Continuing\\..*Breakpoint \[0-9\]+, marker \\(\\) at.*" \
+	    "continue to marker ($syscall)"
+    }
+}
+
 disp_step_cross_syscall "fork"
 disp_step_cross_syscall "vfork"
+
+set testfile "disp-step-fork"
+clean_restart $testfile
+if { ![runto main] } then {
+    fail "run to main"
+    return -1
+}
+
+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 } {
+    break_cond_on_syscall "fork"
+    break_cond_on_syscall "vfork"
+}