gdb/

	Fix disp-step-syscall.exp: fork: single step over fork.
	* i386-linux-tdep.c (-i386_linux_get_syscall_number): Rename to ...
	(i386_linux_get_syscall_number_from_regcache): ... here, new function
	comment, change parameters gdbarch and ptid to regcache.  Remove
	parameter regcache, initialize gdbarch from regcache here.
	(i386_linux_get_syscall_number, i386_linux_displaced_step_copy_insn):
	New functions.
	(i386_linux_init_abi): Install i386_linux_displaced_step_copy_insn
	instead.
	* i386-tdep.c (i386_syscall_p): Check also for 'sysenter' and
	'syscall'.  Make the 'int' check more strict.

gdb/testsuite/
	Fix disp-step-syscall.exp: fork: single step over fork.
	* gdb.base/disp-step-syscall.exp (syscall_insn): Anchor it by
	whitespaces.
	(single step over $syscall): Remove its check.
	(single step over $syscall final pc): New check.

1 files changed, 65 insertions, 4 deletions

diff --git a/gdb/i386-linux-tdep.c b/gdb/i386-linux-tdep.c
index 13857e5235f..bfb0e1c7071 100644
--- a/gdb/i386-linux-tdep.c
+++ b/gdb/i386-linux-tdep.c
@@ -491,11 +491,17 @@ i386_linux_record_signal (struct gdbarch *gdbarch,
 }
 
 
+/* Core of the implementation for gdbarch get_syscall_number.  Get pending
+   syscall number from REGCACHE.  If there is no pending syscall -1 will be
+   returned.  Pending syscall means ptrace has stepped into the syscall but
+   another ptrace call will step out.  PC is right after the int $0x80
+   / syscall / sysenter instruction in both cases, PC does not change during
+   the second ptrace step.  */
+
 static LONGEST
-i386_linux_get_syscall_number (struct gdbarch *gdbarch,
-                               ptid_t ptid)
+i386_linux_get_syscall_number_from_regcache (struct regcache *regcache)
 {
-  struct regcache *regcache = get_thread_regcache (ptid);
+  struct gdbarch *gdbarch = get_regcache_arch (regcache);
   enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
   /* The content of a register.  */
   gdb_byte buf[4];
@@ -512,6 +518,18 @@ i386_linux_get_syscall_number (struct gdbarch *gdbarch,
   return ret;
 }
 
+/* Wrapper for i386_linux_get_syscall_number_from_regcache to make it
+   compatible with gdbarch get_syscall_number method prototype.  */
+
+static LONGEST
+i386_linux_get_syscall_number (struct gdbarch *gdbarch,
+                               ptid_t ptid)
+{
+  struct regcache *regcache = get_thread_regcache (ptid);
+
+  return i386_linux_get_syscall_number_from_regcache (regcache);
+}
+
 /* The register sets used in GNU/Linux ELF core-dumps are identical to
    the register sets in `struct user' that are used for a.out
    core-dumps.  These are also used by ptrace(2).  The corresponding
@@ -643,6 +661,49 @@ i386_linux_core_read_description (struct gdbarch *gdbarch,
     return tdesc_i386_mmx_linux;
 }
 
+/* Linux kernel shows PC value after the 'int $0x80' instruction even if
+   inferior is still inside the syscall.  On next PTRACE_SINGLESTEP it will
+   finish the syscall but PC will not change.
+   
+   Some vDSOs contain 'int $0x80; ret' and during stepping out of the syscall
+   i386_displaced_step_fixup would keep PC at the displaced pad location.
+   As PC is pointing to the 'ret' instruction before the step
+   i386_displaced_step_fixup would expect inferior has just executed that 'ret'
+   and PC should not be adjusted.  In reality it finished syscall instead and
+   PC should get relocated back to its vDSO address.  Hide the 'ret'
+   instruction by 'nop' so that i386_displaced_step_fixup is not confused.
+   
+   It is not fully correct as the bytes in struct displaced_step_closure will
+   not match the inferior code.  But we would need some new flag in
+   displaced_step_closure otherwise to keep the state that syscall is finishing
+   for the later i386_displaced_step_fixup execution as the syscall execution
+   is already no longer detectable there.  The new flag field would mean
+   i386-linux-tdep.c needs to wrap all the displacement methods of i386-tdep.c
+   which does not seem worth it.  The same effect is achieved by patching that
+   'nop' instruction there instead.  */
+
+struct displaced_step_closure *
+i386_linux_displaced_step_copy_insn (struct gdbarch *gdbarch,
+				     CORE_ADDR from, CORE_ADDR to,
+				     struct regcache *regs)
+{
+  struct displaced_step_closure *closure;
+  
+  closure = i386_displaced_step_copy_insn (gdbarch, from, to, regs);
+
+  if (i386_linux_get_syscall_number_from_regcache (regs) != -1)
+    {
+      /* Since we use simple_displaced_step_copy_insn, our closure is a
+	 copy of the instruction.  */
+      gdb_byte *insn = (gdb_byte *) closure;
+
+      /* Fake nop.  */
+      insn[0] = 0x90;
+    }
+
+  return closure;
+}
+
 static void
 i386_linux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
 {
@@ -891,7 +952,7 @@ i386_linux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
 
   /* Displaced stepping.  */
   set_gdbarch_displaced_step_copy_insn (gdbarch,
-                                        i386_displaced_step_copy_insn);
+                                        i386_linux_displaced_step_copy_insn);
   set_gdbarch_displaced_step_fixup (gdbarch, i386_displaced_step_fixup);
   set_gdbarch_displaced_step_free_closure (gdbarch,
                                            simple_displaced_step_free_closure);