[Qemu-devel] [7194] MIPS signal handling fixes.

[Paul Brook]

Revision: 7194
          http://svn.sv.gnu.org/viewvc/?view=rev&root=qemu&revision=7194
Author:   pbrook
Date:     2009-04-21 01:41:10 +0000 (Tue, 21 Apr 2009)
Log Message:
-----------
MIPS signal handling fixes.

Also fixes a register corruption bug in do_sigreturn. When "returning"
from sigreturn we are actually restoring the virtual cpu state from the
signal frame.  This is actually surprisingly hard to observe in practice.

Typically an thread be blocked in a FUTEX_WAIT call when the signal arrives,
so the effect is a spurious syscall success and the introduction of a
subtle race condition.

On x86/arm a syscall modifies a single word sized register, so
do_sigreturn can just return that value.  On MIPS a syscall clobbers
multiple registers, so we need additional smarts.  My solution is to
invent a magic errno value that means "don't touch CPU state".

Modified Paths:
--------------
    trunk/linux-user/main.c
    trunk/linux-user/mips/syscall.h
    trunk/linux-user/signal.c

Modified: trunk/linux-user/main.c
===================================================================
--- trunk/linux-user/main.c     2009-04-21 01:03:10 UTC (rev 7193)
+++ trunk/linux-user/main.c     2009-04-21 01:41:10 UTC (rev 7194)
@@ -1858,6 +1858,11 @@
                                  env->active_tc.gpr[7],
                                  arg5, arg6/*, arg7, arg8*/);
             }
+            if (ret == -TARGET_QEMU_ESIGRETURN) {
+                /* Returning from a successful sigreturn syscall.
+                   Avoid clobbering register state.  */
+                break;
+            }
             if ((unsigned int)ret >= (unsigned int)(-1133)) {
                 env->active_tc.gpr[7] = 1; /* error flag */
                 ret = -ret;

Modified: trunk/linux-user/mips/syscall.h
===================================================================
--- trunk/linux-user/mips/syscall.h     2009-04-21 01:03:10 UTC (rev 7193)
+++ trunk/linux-user/mips/syscall.h     2009-04-21 01:41:10 UTC (rev 7194)
@@ -221,4 +221,7 @@
 
 
 
+/* Nasty hack: define a fake errno value for use by sigreturn.  */
+#define TARGET_QEMU_ESIGRETURN 255
+
 #define UNAME_MACHINE "mips"

Modified: trunk/linux-user/signal.c
===================================================================
--- trunk/linux-user/signal.c   2009-04-21 01:03:10 UTC (rev 7193)
+++ trunk/linux-user/signal.c   2009-04-21 01:41:10 UTC (rev 7194)
@@ -2313,6 +2313,21 @@
     target_sigset_t sf_mask;
 };
 
+struct target_ucontext {
+    target_ulong uc_flags;
+    target_ulong uc_link;
+    target_stack_t uc_stack;
+    struct target_sigcontext uc_mcontext;
+    target_sigset_t uc_sigmask;
+};
+
+struct target_rt_sigframe {
+    uint32_t rs_ass[4];               /* argument save space for o32 */
+    uint32_t rs_code[2];              /* signal trampoline */
+    struct target_siginfo rs_info;
+    struct target_ucontext rs_uc;
+};
+
 /* Install trampoline to jump back from signal handler */
 static inline int install_sigtramp(unsigned int *tramp,   unsigned int syscall)
 {
@@ -2592,7 +2607,7 @@
     /* I am not sure this is right, but it seems to work
     * maybe a problem with nested signals ? */
     regs->CP0_EPC = 0;
-    return 0;
+    return -TARGET_QEMU_ESIGRETURN;
 
 badframe:
     force_sig(TARGET_SIGSEGV/*, current*/);
@@ -2603,13 +2618,95 @@
                            target_siginfo_t *info,
                           target_sigset_t *set, CPUState *env)
 {
-    fprintf(stderr, "setup_rt_frame: not implemented\n");
+    struct target_rt_sigframe *frame;
+    abi_ulong frame_addr;
+    int i;
+
+    frame_addr = get_sigframe(ka, env, sizeof(*frame));
+    if (!lock_user_struct(VERIFY_WRITE, frame, frame_addr, 0))
+       goto give_sigsegv;
+
+    install_sigtramp(frame->rs_code, TARGET_NR_rt_sigreturn);
+
+    copy_siginfo_to_user(&frame->rs_info, info);
+
+    __put_user(0, &frame->rs_uc.uc_flags);
+    __put_user(0, &frame->rs_uc.uc_link);
+    __put_user(target_sigaltstack_used.ss_sp, &frame->rs_uc.uc_stack.ss_sp);
+    __put_user(target_sigaltstack_used.ss_size, 
&frame->rs_uc.uc_stack.ss_size);
+    __put_user(sas_ss_flags(get_sp_from_cpustate(env)),
+               &frame->rs_uc.uc_stack.ss_flags);
+
+    setup_sigcontext(env, &frame->rs_uc.uc_mcontext);
+
+    for(i = 0; i < TARGET_NSIG_WORDS; i++) {
+        __put_user(set->sig[i], &frame->rs_uc.uc_sigmask.sig[i]);
+    }
+
+    /*
+    * Arguments to signal handler:
+    *
+    *   a0 = signal number
+    *   a1 = pointer to struct siginfo
+    *   a2 = pointer to struct ucontext
+    *
+    * $25 and PC point to the signal handler, $29 points to the
+    * struct sigframe.
+    */
+    env->active_tc.gpr[ 4] = sig;
+    env->active_tc.gpr[ 5] = frame_addr
+                             + offsetof(struct target_rt_sigframe, rs_info);
+    env->active_tc.gpr[ 6] = frame_addr
+                             + offsetof(struct target_rt_sigframe, rs_uc);
+    env->active_tc.gpr[29] = frame_addr;
+    env->active_tc.gpr[31] = frame_addr
+                             + offsetof(struct target_rt_sigframe, rs_code);
+    /* The original kernel code sets CP0_EPC to the handler
+    * since it returns to userland using eret
+    * we cannot do this here, and we must set PC directly */
+    env->active_tc.PC = env->active_tc.gpr[25] = ka->_sa_handler;
+    unlock_user_struct(frame, frame_addr, 1);
+    return;
+
+give_sigsegv:
+    unlock_user_struct(frame, frame_addr, 1);
+    force_sig(TARGET_SIGSEGV/*, current*/);
+    return;
 }
 
 long do_rt_sigreturn(CPUState *env)
 {
-    fprintf(stderr, "do_rt_sigreturn: not implemented\n");
-    return -TARGET_ENOSYS;
+    struct target_rt_sigframe *frame;
+    abi_ulong frame_addr;
+    sigset_t blocked;
+
+#if defined(DEBUG_SIGNAL)
+    fprintf(stderr, "do_rt_sigreturn\n");
+#endif
+    frame_addr = env->active_tc.gpr[29];
+    if (!lock_user_struct(VERIFY_READ, frame, frame_addr, 1))
+       goto badframe;
+
+    target_to_host_sigset(&blocked, &frame->rs_uc.uc_sigmask);
+    sigprocmask(SIG_SETMASK, &blocked, NULL);
+
+    if (restore_sigcontext(env, &frame->rs_uc.uc_mcontext))
+        goto badframe;
+
+    if (do_sigaltstack(frame_addr +
+                      offsetof(struct target_rt_sigframe, rs_uc.uc_stack),
+                      0, get_sp_from_cpustate(env)) == -EFAULT)
+        goto badframe;
+
+    env->active_tc.PC = env->CP0_EPC;
+    /* I am not sure this is right, but it seems to work
+    * maybe a problem with nested signals ? */
+    env->CP0_EPC = 0;
+    return -TARGET_QEMU_ESIGRETURN;
+
+badframe:
+    force_sig(TARGET_SIGSEGV/*, current*/);
+    return 0;
 }
 
 #elif defined(TARGET_SH4)