fix skipping permanent breakpoints

The gdb.arch/i386-bp_permanent.exp test is currently failing an
assertion recently added:

 (gdb) stepi
 ../../src/gdb/infrun.c:2237: internal-error: resume: Assertion `sig != GDB_SIGNAL_0' failed.
 A problem internal to GDB has been detected,
 further debugging may prove unreliable.
 Quit this debugging session? (y or n)
 FAIL: gdb.arch/i386-bp_permanent.exp: Single stepping past permanent breakpoint. (GDB internal error)

The assertion expects that the only reason we currently need to step a
breakpoint instruction is when we have a signal to deliver.  But when
stepping a permanent breakpoint (with or without a signal) we also
reach this code.

The assertion is correct and the permanent breakpoints skipping code
is wrong.

Consider the case of the user doing "step/stepi" when stopped at a
permanent breakpoint.  GDB's `resume' calls the
gdbarch_skip_permanent_breakpoint hook and then happily continues
stepping:

  /* Normally, by the time we reach `resume', the breakpoints are either
     removed or inserted, as appropriate.  The exception is if we're sitting
     at a permanent breakpoint; we need to step over it, but permanent
     breakpoints can't be removed.  So we have to test for it here.  */
  if (breakpoint_here_p (aspace, pc) == permanent_breakpoint_here)
    {
      gdbarch_skip_permanent_breakpoint (gdbarch, regcache);
    }

But since gdbarch_skip_permanent_breakpoint already advanced the PC
manually, this ends up executing the instruction that is _after_ the
breakpoint instruction.  The user-visible result is that a single-step
steps two instructions.

The gdb.arch/i386-bp_permanent.exp test is actually ensuring that
that's indeed how things work.  It runs to an int3 instruction, does
"stepi", and checks that "leave" was executed with that "stepi".  Like
this:

 (gdb) b *0x0804848c
 Breakpoint 2 at 0x804848c
 (gdb) c
 Continuing.

 Breakpoint 2, 0x0804848c in standard ()
 (gdb) disassemble
 Dump of assembler code for function standard:
    0x08048488 <+0>:     push   %ebp
    0x08048489 <+1>:     mov    %esp,%ebp
    0x0804848b <+3>:     push   %edi
 => 0x0804848c <+4>:     int3
    0x0804848d <+5>:     leave
    0x0804848e <+6>:     ret
    0x0804848f <+7>:     nop
 (gdb) si
 0x0804848e in standard ()
 (gdb) disassemble
 Dump of assembler code for function standard:
    0x08048488 <+0>:     push   %ebp
    0x08048489 <+1>:     mov    %esp,%ebp
    0x0804848b <+3>:     push   %edi
    0x0804848c <+4>:     int3
    0x0804848d <+5>:     leave
 => 0x0804848e <+6>:     ret
    0x0804848f <+7>:     nop
 End of assembler dump.
 (gdb)

One would instead expect that a stepi at 0x0804848c stops at
0x0804848d, _before_ the "leave" is executed.  This commit changes GDB
this way.  Care is taken to make stepping into a signal handler when
the step starts at a permanent breakpoint instruction work correctly.

The patch adjusts gdb.arch/i386-bp_permanent.exp in this direction,
and also makes it work on x86_64 (currently it only works on i*86).

The patch also adds a new gdb.base/bp-permanent.exp test that
exercises many different code paths related to stepping permanent
breakpoints, including the stepping with signals cases.  The test uses
"hack/trick" to make it work on all (or most) platforms -- it doesn't
really hard code a breakpoint instruction.

Tested on x86_64 Fedora 20, native and gdbserver.

gdb/
2014-11-12  Pedro Alves  <palves@redhat.com>

	* infrun.c (resume): Clear the thread's 'stepped_breakpoint' flag.
	Rewrite stepping over a permanent breakpoint.
	(thread_still_needs_step_over, proceed): Don't set
	stepping_over_breakpoint for permanent breakpoints.
	(handle_signal_stop): Don't clear stepped_breakpoint.  Also pull
	single-step breakpoints out of the target on hardware step
	targets.
	(process_event_stop_test): If stepping a permanent breakpoint
	doesn't hit the step-resume breakpoint, delete the step-resume
	breakpoint.
	(switch_back_to_stepped_thread): Also check if the stepped thread
	has advanced already on hardware step targets.
	(currently_stepping): Return true if the thread stepped a
	breakpoint.

gdb/testsuite/
2014-11-12  Pedro Alves  <palves@redhat.com>

	* gdb.arch/i386-bp_permanent.c: New file.
	* gdb.arch/i386-bp_permanent.exp: Don't skip on x86_64.
	(srcfile): Set to i386-bp_permanent.c.
	(top level): Adjust to work in both 32-bit and 64-bit modes.  Test
	that stepi does not execute the 'leave' instruction, instead of
	testing it does execute.
	* gdb.base/bp-permanent.c: New file.
	* gdb.base/bp-permanent.exp: New file.

2 files changed, 78 insertions, 28 deletions

diff --git a/gdb/testsuite/gdb.arch/i386-bp_permanent.c b/gdb/testsuite/gdb.arch/i386-bp_permanent.c
new file mode 100644
index 0000000..dc36d89
--- /dev/null
+++ b/gdb/testsuite/gdb.arch/i386-bp_permanent.c
@@ -0,0 +1,57 @@
+/* Copyright (C) 2003-2014 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#ifdef SYMBOL_PREFIX
+#define SYMBOL(str)	SYMBOL_PREFIX #str
+#else
+#define SYMBOL(str)	#str
+#endif
+
+int
+main (void)
+{
+  standard ();
+  return 0;
+}
+
+/* A normal prologue.  */
+
+#ifdef __x86_64__
+asm(".text\n"
+    "    .align 8\n"
+    SYMBOL (standard) ":\n"
+    "    push %rbp\n"
+    "    mov  %rsp, %rbp\n"
+    "    push %rdi\n"
+    "    int3\n"
+    "    leaveq\n"
+    "    retq\n");
+
+#else
+
+asm(".text\n"
+    "    .align 8\n"
+    "    .global " SYMBOL(standard) "\n"
+    SYMBOL (standard) ":\n"
+    "    pushl %ebp\n"
+    "    movl  %esp, %ebp\n"
+    "    pushl %edi\n"
+    "    int3\n"
+    "    leave\n"
+    "    ret\n");
+
+#endif
diff --git a/gdb/testsuite/gdb.arch/i386-bp_permanent.exp b/gdb/testsuite/gdb.arch/i386-bp_permanent.exp
index 6be1626..833b4ed 100644
--- a/gdb/testsuite/gdb.arch/i386-bp_permanent.exp
+++ b/gdb/testsuite/gdb.arch/i386-bp_permanent.exp
@@ -18,13 +18,13 @@
 
 # Test stepping over permanent breakpoints on i386.
 
-if { ![is_x86_like_target] } then {
+if { ![istarget "i?86-*-*"] && ![istarget "x86_64-*-*"] } then {
     verbose "Skipping skip over permanent breakpoint on i386 tests."
     return
 }
 
 set testfile "i386-bp_permanent"
-set srcfile i386-prologue.c
+set srcfile i386-bp_permanent.c
 set binfile ${objdir}/${subdir}/${testfile}
 
 # some targets have leading underscores on assembly symbols.
@@ -51,14 +51,12 @@ if ![runto_main] then {
   return -1
 }
 
-set function standard
+set function "standard"
 
 set retcode [gdb_test_multiple "disassemble $function" "Disassemble function '$function'" {
-    -re ".*($hex) <\\+0>.*($hex) <\\+4>.*($hex) <\\+5>.*($hex) <\\+6>.*$gdb_prompt $" {
-      set function_start $expect_out(1,string)
-      set address $expect_out(2,string)
-      set address1 $expect_out(3,string)
-      set address2 $expect_out(4,string)
+    -re "($hex) <\\+0>.*($hex) <\\+$decimal>.*int3.*($hex) <\\+$decimal>.*leave.*$gdb_prompt $" {
+      set address_bp $expect_out(2,string)
+      set address_after_bp $expect_out(3,string)
     }
 }]
 
@@ -67,30 +65,25 @@ if {$retcode != 0} {
   return -1
 }
 
-gdb_breakpoint "*$function_start"
+gdb_breakpoint "*$address_bp"
 
-gdb_breakpoint "*$address"
+gdb_test "continue" "Breakpoint .*, $address_bp in $function.*" \
+	 "stop at permanent breakpoint"
 
-gdb_test "continue" "Breakpoint .*, $function_start in $function.*" \
-	 "Stop at the '$function' start breakpoint (fetching esp)."
-
-# We want to fetch esp at the start of '$function' function to make sure
-# skip_permanent_breakpoint implementation really skips only the perm. 
-# breakpoint. If, for whatever reason, 'leave' instruction doesn't get
-# executed, esp will not have this value.
-set start_esp 0
-gdb_test_multiple "print \$esp" "Fetch esp value." {
+# We want to fetch the stack pointer at the start of '$function'
+# function to make sure the skip_permanent_breakpoint implementation
+# really skips only the permanent breakpoint.  If, for whatever
+# reason, the 'leave' instruction executes, the stack pointer will not
+# have this value.
+set start_sp 0
+gdb_test_multiple "print \$sp" "fetch stack pointer value" {
     -re "\\\$1.*($hex).*$gdb_prompt $" {
-      set start_esp $expect_out(1,string)
+      set start_sp $expect_out(1,string)
     }
 }
 
-gdb_test "continue" "Breakpoint .*, $address in $function.*" \
-	 "Stop at permanent breakpoint."
-
-gdb_test "stepi" "$address1|$address2 in $function.*" \
-	 "Single stepping past permanent breakpoint."
-
-gdb_test "print \$esp" ".*$start_esp.*" \
-	 "ESP value does not match - step_permanent_breakpoint wrong."
+gdb_test "stepi" "$address_after_bp in $function.*" \
+	 "single-step past permanent breakpoint"
 
+gdb_test "print \$sp" ".*$start_sp.*" \
+	 "stack pointer value matches"