uml: work around broken host PTRACE_SYSEMU

Fedora broke PTRACE_SYSEMU again, and UML crashes as a result when it
doesn't need to.  This patch makes the PTRACE_SYSEMU check fail gracefully
and makes UML fall back to PTRACE_SYSCALL.

Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/arch/um/os-Linux/start_up.c b/arch/um/os-Linux/start_up.c
index b4b36e0..183db26 100644 (file)
--- a/arch/um/os-Linux/start_up.c
+++ b/arch/um/os-Linux/start_up.c
@@ -121,8 +121,10 @@ static int stop_ptraced_child(int pid, int exitcode, int mustexit)
 {
        int status, n, ret = 0;
 
-       if (ptrace(PTRACE_CONT, pid, 0, 0) < 0)
-               fatal_perror("stop_ptraced_child : ptrace failed");
+       if (ptrace(PTRACE_CONT, pid, 0, 0) < 0) {
+               perror("stop_ptraced_child : ptrace failed");
+               return -1;
+       }
        CATCH_EINTR(n = waitpid(pid, &status, 0));
        if (!WIFEXITED(status) || (WEXITSTATUS(status) != exitcode)) {
                int exit_with = WEXITSTATUS(status);
@@ -212,7 +214,7 @@ static void __init check_sysemu(void)
        if (n < 0)
                fatal_perror("check_sysemu : wait failed");
        if (!WIFSTOPPED(status) || (WSTOPSIG(status) != SIGTRAP))
-               fatal("check_sysemu : expected SIGTRAP, got status = %d",
+               fatal("check_sysemu : expected SIGTRAP, got status = %d\n",
                      status);
 
        if (ptrace(PTRACE_GETREGS, pid, 0, regs) < 0)
@@ -254,9 +256,11 @@ static void __init check_sysemu(void)
 
                if (WIFSTOPPED(status) &&
                    (WSTOPSIG(status) == (SIGTRAP|0x80))) {
-                       if (!count)
-                               fatal("check_ptrace : SYSEMU_SINGLESTEP "
-                                     "doesn't singlestep");
+                       if (!count) {
+                               non_fatal("check_ptrace : SYSEMU_SINGLESTEP "
+                                         "doesn't singlestep");
+                               goto fail;
+                       }
                        n = ptrace(PTRACE_POKEUSR, pid, PT_SYSCALL_RET_OFFSET,
                                   os_getpid());
                        if (n < 0)
@@ -266,9 +270,12 @@ static void __init check_sysemu(void)
                }
                else if (WIFSTOPPED(status) && (WSTOPSIG(status) == SIGTRAP))
                        count++;
-               else
-                       fatal("check_ptrace : expected SIGTRAP or "
-                             "(SIGTRAP | 0x80), got status = %d", status);
+               else {
+                       non_fatal("check_ptrace : expected SIGTRAP or "
+                                 "(SIGTRAP | 0x80), got status = %d\n",
+                                 status);
+                       goto fail;
+               }
        }
        if (stop_ptraced_child(pid, 0, 0) < 0)
                goto fail_stopped;