[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>

diff --git a/arch/i386/kernel/ptrace.c b/arch/i386/kernel/ptrace.c
index 18642f0..3196ba5 100644 (file)
--- 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;

diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
index 7528afb..2afdafb 100644 (file)
--- a/include/linux/ptrace.h
+++ b/include/linux/ptrace.h
@@ -21,6 +21,7 @@
 
 #define PTRACE_SYSCALL           24
 #define PTRACE_SYSEMU            31
+#define PTRACE_SYSEMU_SINGLESTEP  32
 
 /* 0x4200-0x4300 are reserved for architecture-independent additions.  */
 #define PTRACE_SETOPTIONS      0x4200