[PATCH] Uml support: add PTRACE_SYSEMU_SINGLESTEP option to i386

This patch implements the new ptrace option PTRACE_SYSEMU_SINGLESTEP, which
can be used by UML to singlestep a process: it will receive SINGLESTEP
interceptions for normal instructions and syscalls, but syscall execution will
be skipped just like with PTRACE_SYSEMU.

Signed-off-by: Bodo Stroesser <bstroesser@fujitsu-siemens.com>
Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Cc: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 17 insertions, 4 deletions

diff --git a/arch/i386/kernel/ptrace.c b/arch/i386/kernel/ptrace.c
index 18642f05dde1..3196ba50fcd5 100644
--- a/arch/i386/kernel/ptrace.c
+++ b/arch/i386/kernel/ptrace.c
@@ -547,11 +547,17 @@ asmlinkage int sys_ptrace(long request, long pid, long addr, long data)
                 wake_up_process(child);
                 break;
 
+        case PTRACE_SYSEMU_SINGLESTEP: /* Same as SYSEMU, but singlestep if not syscall */
         case PTRACE_SINGLESTEP: /* set the trap flag. */
                 ret = -EIO;
                 if (!valid_signal(data))
                         break;
-                clear_tsk_thread_flag(child, TIF_SYSCALL_EMU);
+
+                if (request == PTRACE_SYSEMU_SINGLESTEP)
+                        set_tsk_thread_flag(child, TIF_SYSCALL_EMU);
+                else
+                        clear_tsk_thread_flag(child, TIF_SYSCALL_EMU);
+
                 clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
                 set_singlestep(child);
                 child->exit_code = data;
@@ -686,7 +692,10 @@ void send_sigtrap(struct task_struct *tsk, struct pt_regs *regs, int error_code)
 __attribute__((regparm(3)))
 int do_syscall_trace(struct pt_regs *regs, int entryexit)
 {
-        int is_sysemu, is_singlestep, ret = 0;
+        int is_sysemu = test_thread_flag(TIF_SYSCALL_EMU), ret = 0;
+        /* With TIF_SYSCALL_EMU set we want to ignore TIF_SINGLESTEP */
+        int is_singlestep = !is_sysemu && test_thread_flag(TIF_SINGLESTEP);
+
         /* do the secure computing check first */
         secure_computing(regs->orig_eax);
 
@@ -696,8 +705,11 @@ int do_syscall_trace(struct pt_regs *regs, int entryexit)
         if (!(current->ptrace & PT_PTRACED))
                 goto out;
 
-        is_sysemu = test_thread_flag(TIF_SYSCALL_EMU);
-        is_singlestep = test_thread_flag(TIF_SINGLESTEP);
+        /* If a process stops on the 1st tracepoint with SYSCALL_TRACE
+         * and then is resumed with SYSEMU_SINGLESTEP, it will come in
+         * here. We have to check this and return */
+        if (is_sysemu && entryexit)
+                return 0;
 
         /* Fake a debug trap */
         if (is_singlestep)
@@ -728,6 +740,7 @@ int do_syscall_trace(struct pt_regs *regs, int entryexit)
         if (ret == 0)
                 return 0;
 
+        regs->orig_eax = -1; /* force skip of syscall restarting */
         if (unlikely(current->audit_context))
                 audit_syscall_exit(current, AUDITSC_RESULT(regs->eax), regs->eax);
         return 1;