Re: [Qemu-devel] [PATCH 2/3] linux-user: ppc signal handling

[Nathan Froyd <froydnj@codesourcery.com>]

Implement setup_{,rt_}frame and do_{,rt_}sigreturn for PPC 32-bit.  Use
the same TARGET_QEMU_ESIGRETURN hack as for MIPS to avoid clobbering
register state on a sigreturn.

Signed-off-by: Nathan Froyd <froydnj@codesourcery.com>
---
Remove the trailing whitespace and tabs that malc noticed.

 linux-user/main.c        |    5 +
 linux-user/ppc/syscall.h |    3 +
 linux-user/signal.c      |  596 ++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 604 insertions(+), 0 deletions(-)

diff --git a/linux-user/main.c b/linux-user/main.c
index dc39b05..9c57c17 100644
--- a/linux-user/main.c
+++ b/linux-user/main.c
@@ -1461,6 +1461,11 @@ void cpu_loop(CPUPPCState *env)
             ret = do_syscall(env, env->gpr[0], env->gpr[3], env->gpr[4],
                              env->gpr[5], env->gpr[6], env->gpr[7],
                              env->gpr[8]);
+            if (ret == (uint32_t)(-TARGET_QEMU_ESIGRETURN)) {
+                /* Returning from a successful sigreturn syscall.
+                   Avoid corrupting register state.  */
+                break;
+            }
             if (ret > (uint32_t)(-515)) {
                 env->crf[0] |= 0x1;
                 ret = -ret;
diff --git a/linux-user/ppc/syscall.h b/linux-user/ppc/syscall.h
index a21d61b..d789911 100644
--- a/linux-user/ppc/syscall.h
+++ b/linux-user/ppc/syscall.h
@@ -51,6 +51,9 @@ struct target_revectored_struct {
 	abi_ulong __map[8];			/* 256 bits */
 };
 
+/* Nasty hack: define a fake errno value for use by sigreturn.  */
+#define TARGET_QEMU_ESIGRETURN 255
+
 /*
  * flags masks
  */
diff --git a/linux-user/signal.c b/linux-user/signal.c
index 742d52a..9c9c7eb 100644
--- a/linux-user/signal.c
+++ b/linux-user/signal.c
@@ -3182,6 +3182,602 @@ long do_rt_sigreturn(CPUState *env)
     return -TARGET_ENOSYS;
 }
 
+#elif defined(TARGET_PPC) && !defined(TARGET_PPC64)
+
+/* FIXME: Many of the structures are defined for both PPC and PPC64, but
+   the signal handling is different enough that we haven't implemented
+   support for PPC64 yet.  Hence the restriction above.
+
+   There are various #if'd blocks for code for TARGET_PPC64.  These
+   blocks should go away so that we can successfully run 32-bit and
+   64-bit binaries on a QEMU configured for PPC64.  */
+
+/* Size of dummy stack frame allocated when calling signal handler.
+   See arch/powerpc/include/asm/ptrace.h.  */
+#if defined(TARGET_PPC64)
+#define SIGNAL_FRAMESIZE 128
+#else
+#define SIGNAL_FRAMESIZE 64
+#endif
+
+/* See arch/powerpc/include/asm/sigcontext.h.  */
+struct target_sigcontext {
+    target_ulong _unused[4];
+    int32_t signal;
+#if defined(TARGET_PPC64)
+    int32_t pad0;
+#endif
+    target_ulong handler;
+    target_ulong oldmask;
+    target_ulong regs;      /* struct pt_regs __user * */
+    /* TODO: PPC64 includes extra bits here.  */
+};
+
+/* Indices for target_mcontext.mc_gregs, below.
+   See arch/powerpc/include/asm/ptrace.h for details.  */
+enum {
+    TARGET_PT_R0 = 0,
+    TARGET_PT_R1 = 1,
+    TARGET_PT_R2 = 2,
+    TARGET_PT_R3 = 3,
+    TARGET_PT_R4 = 4,
+    TARGET_PT_R5 = 5,
+    TARGET_PT_R6 = 6,
+    TARGET_PT_R7 = 7,
+    TARGET_PT_R8 = 8,
+    TARGET_PT_R9 = 9,
+    TARGET_PT_R10 = 10,
+    TARGET_PT_R11 = 11,
+    TARGET_PT_R12 = 12,
+    TARGET_PT_R13 = 13,
+    TARGET_PT_R14 = 14,
+    TARGET_PT_R15 = 15,
+    TARGET_PT_R16 = 16,
+    TARGET_PT_R17 = 17,
+    TARGET_PT_R18 = 18,
+    TARGET_PT_R19 = 19,
+    TARGET_PT_R20 = 20,
+    TARGET_PT_R21 = 21,
+    TARGET_PT_R22 = 22,
+    TARGET_PT_R23 = 23,
+    TARGET_PT_R24 = 24,
+    TARGET_PT_R25 = 25,
+    TARGET_PT_R26 = 26,
+    TARGET_PT_R27 = 27,
+    TARGET_PT_R28 = 28,
+    TARGET_PT_R29 = 29,
+    TARGET_PT_R30 = 30,
+    TARGET_PT_R31 = 31,
+    TARGET_PT_NIP = 32,
+    TARGET_PT_MSR = 33,
+    TARGET_PT_ORIG_R3 = 34,
+    TARGET_PT_CTR = 35,
+    TARGET_PT_LNK = 36,
+    TARGET_PT_XER = 37,
+    TARGET_PT_CCR = 38,
+    /* Yes, there are two registers with #39.  One is 64-bit only.  */
+    TARGET_PT_MQ = 39,
+    TARGET_PT_SOFTE = 39,
+    TARGET_PT_TRAP = 40,
+    TARGET_PT_DAR = 41,
+    TARGET_PT_DSISR = 42,
+    TARGET_PT_RESULT = 43,
+    TARGET_PT_REGS_COUNT = 44
+};
+
+/* See arch/powerpc/include/asm/ucontext.h.  Only used for 32-bit PPC;
+   on 64-bit PPC, sigcontext and mcontext are one and the same.  */
+struct target_mcontext {
+    target_ulong mc_gregs[48];
+    /* Includes fpscr.  */
+    uint64_t mc_fregs[33];
+    target_ulong mc_pad[2];
+    /* We need to handle Altivec and SPE at the same time, which no
+       kernel needs to do.  Fortunately, the kernel defines this bit to
+       be Altivec-register-large all the time, rather than trying to
+       twiddle it based on the specific platform.  */
+    union {
+        /* SPE vector registers.  One extra for SPEFSCR.  */
+        uint32_t spe[33];
+        /* Altivec vector registers.  The packing of VSCR and VRSAVE
+           varies depending on whether we're PPC64 or not: PPC64 splits
+           them apart; PPC32 stuffs them together.  */
+#if defined(TARGET_PPC64)
+#define NVRREG 34
+#else
+#define NVRREG 33
+#endif
+        ppc_avr_t altivec[NVRREG];
+#undef NVRREG
+    } mc_vregs __attribute__((__aligned__(16)));
+};
+
+struct target_ucontext {
+    target_ulong uc_flags;
+    target_ulong uc_link;    /* struct ucontext __user * */
+    struct target_sigaltstack uc_stack;
+#if !defined(TARGET_PPC64)
+    int32_t uc_pad[7];
+    target_ulong uc_regs;    /* struct mcontext __user *
+                                points to uc_mcontext field */
+#endif
+    target_sigset_t uc_sigmask;
+#if defined(TARGET_PPC64)
+    target_sigset_t unused[15]; /* Allow for uc_sigmask growth */
+    struct target_sigcontext uc_mcontext;
+#else
+    int32_t uc_maskext[30];
+    int32_t uc_pad2[3];
+    struct target_mcontext uc_mcontext;
+#endif
+};
+
+/* See arch/powerpc/kernel/signal_32.c.  */
+struct target_sigframe {
+    struct target_sigcontext sctx;
+    struct target_mcontext mctx;
+    int32_t abigap[56];
+};
+
+struct target_rt_sigframe {
+    struct target_siginfo info;
+    struct target_ucontext uc;
+    int32_t abigap[56];
+};
+
+/* We use the mc_pad field for the signal return trampoline.  */
+#define tramp mc_pad
+
+/* See arch/powerpc/kernel/signal.c.  */
+static target_ulong get_sigframe(struct target_sigaction *ka,
+                                 CPUState *env,
+                                 int frame_size)
+{
+    target_ulong oldsp, newsp;
+
+    oldsp = env->gpr[1];
+
+    if ((ka->sa_flags & TARGET_SA_ONSTACK) &&
+        (sas_ss_flags(oldsp))) {
+        oldsp = (target_sigaltstack_used.ss_sp
+                 + target_sigaltstack_used.ss_size);
+    }
+
+    newsp = (oldsp - frame_size) & ~0xFUL;
+
+    return newsp;
+}
+
+static int save_user_regs(CPUState *env, struct target_mcontext *frame,
+                          int sigret)
+{
+    target_ulong msr = env->msr;
+    int i;
+    target_ulong ccr = 0;
+
+    /* In general, the kernel attempts to be intelligent about what it
+       needs to save for Altivec/FP/SPE registers.  We don't care that
+       much, so we just go ahead and save everything.  */
+
+    /* Save general registers.  */
+    for (i = 0; i < ARRAY_SIZE(env->gpr); i++) {
+        if (__put_user(env->gpr[i], &frame->mc_gregs[i])) {
+            return 1;
+        }
+    }
+    if (__put_user(env->nip, &frame->mc_gregs[TARGET_PT_NIP])
+        || __put_user(env->ctr, &frame->mc_gregs[TARGET_PT_CTR])
+        || __put_user(env->lr, &frame->mc_gregs[TARGET_PT_LNK])
+        || __put_user(env->xer, &frame->mc_gregs[TARGET_PT_XER]))
+        return 1;
+
+    for (i = 0; i < ARRAY_SIZE(env->crf); i++) {
+        ccr |= env->crf[i] << (32 - ((i + 1) * 4));
+    }
+    if (__put_user(ccr, &frame->mc_gregs[TARGET_PT_CCR]))
+        return 1;
+
+    /* Save Altivec registers if necessary.  */
+    if (env->insns_flags & PPC_ALTIVEC) {
+        for (i = 0; i < ARRAY_SIZE(env->avr); i++) {
+            ppc_avr_t *avr = &env->avr[i];
+            ppc_avr_t *vreg = &frame->mc_vregs.altivec[i];
+
+            if (__put_user(avr->u64[0], &vreg->u64[0]) ||
+                __put_user(avr->u64[1], &vreg->u64[1])) {
+                return 1;
+            }
+        }
+        /* Set MSR_VR in the saved MSR value to indicate that
+           frame->mc_vregs contains valid data.  */
+        msr |= MSR_VR;
+        if (__put_user((uint32_t)env->spr[SPR_VRSAVE],
+                       &frame->mc_vregs.altivec[32].u32[3]))
+            return 1;
+    }
+
+    /* Save floating point registers.  */
+    if (env->insns_flags & PPC_FLOAT) {
+        for (i = 0; i < ARRAY_SIZE(env->fpr); i++) {
+            if (__put_user(env->fpr[i], &frame->mc_fregs[i])) {
+                return 1;
+            }
+        }
+        if (__put_user((uint64_t) env->fpscr, &frame->mc_fregs[32]))
+            return 1;
+    }
+
+    /* Save SPE registers.  The kernel only saves the high half.  */
+    if (env->insns_flags & PPC_SPE) {
+#if defined(TARGET_PPC64)
+        for (i = 0; i < ARRAY_SIZE(env->gpr); i++) {
+            if (__put_user(env->gpr[i] >> 32, &frame->mc_vregs.spe[i])) {
+                return 1;
+            }
+        }
+#else
+        for (i = 0; i < ARRAY_SIZE(env->gprh); i++) {
+            if (__put_user(env->gprh[i], &frame->mc_vregs.spe[i])) {
+                return 1;
+            }
+        }
+#endif
+        /* Set MSR_SPE in the saved MSR value to indicate that
+           frame->mc_vregs contains valid data.  */
+        msr |= MSR_SPE;
+        if (__put_user(env->spe_fscr, &frame->mc_vregs.spe[32]))
+            return 1;
+    }
+
+    /* Store MSR.  */
+    if (__put_user(msr, &frame->mc_gregs[TARGET_PT_MSR]))
+        return 1;
+
+    /* Set up the sigreturn trampoline: li r0,sigret; sc.  */
+    if (sigret) {
+        if (__put_user(0x38000000UL | sigret, &frame->tramp[0]) ||
+            __put_user(0x44000002UL, &frame->tramp[1])) {
+            return 1;
+        }
+    }
+
+    return 0;
+}
+
+static int restore_user_regs(CPUState *env,
+                             struct target_mcontext *frame, int sig)
+{
+    target_ulong save_r2 = 0;
+    target_ulong msr;
+    target_ulong ccr;
+
+    int i;
+
+    if (!sig) {
+        save_r2 = env->gpr[2];
+    }
+
+    /* Restore general registers.  */
+    for (i = 0; i < ARRAY_SIZE(env->gpr); i++) {
+        if (__get_user(env->gpr[i], &frame->mc_gregs[i])) {
+            return 1;
+        }
+    }
+    if (__get_user(env->nip, &frame->mc_gregs[TARGET_PT_NIP])
+        || __get_user(env->ctr, &frame->mc_gregs[TARGET_PT_CTR])
+        || __get_user(env->lr, &frame->mc_gregs[TARGET_PT_LNK])
+        || __get_user(env->xer, &frame->mc_gregs[TARGET_PT_XER]))
+        return 1;
+    if (__get_user(ccr, &frame->mc_gregs[TARGET_PT_CCR]))
+        return 1;
+
+    for (i = 0; i < ARRAY_SIZE(env->crf); i++) {
+        env->crf[i] = (ccr >> (32 - ((i + 1) * 4))) & 0xf;
+    }
+
+    if (!sig) {
+        env->gpr[2] = save_r2;
+    }
+    /* Restore MSR.  */
+    if (__get_user(msr, &frame->mc_gregs[TARGET_PT_MSR]))
+        return 1;
+
+    /* If doing signal return, restore the previous little-endian mode.  */
+    if (sig)
+        env->msr = (env->msr & ~MSR_LE) | (msr & MSR_LE);
+
+    /* Restore Altivec registers if necessary.  */
+    if (env->insns_flags & PPC_ALTIVEC) {
+        for (i = 0; i < ARRAY_SIZE(env->avr); i++) {
+            ppc_avr_t *avr = &env->avr[i];
+            ppc_avr_t *vreg = &frame->mc_vregs.altivec[i];
+
+            if (__get_user(avr->u64[0], &vreg->u64[0]) ||
+                __get_user(avr->u64[1], &vreg->u64[1])) {
+                return 1;
+            }
+        }
+        /* Set MSR_VEC in the saved MSR value to indicate that
+           frame->mc_vregs contains valid data.  */
+        if (__get_user(env->spr[SPR_VRSAVE],
+                       (target_ulong *)(&frame->mc_vregs.altivec[32].u32[3])))
+            return 1;
+    }
+
+    /* Restore floating point registers.  */
+    if (env->insns_flags & PPC_FLOAT) {
+        uint64_t fpscr;
+        for (i = 0; i < ARRAY_SIZE(env->fpr); i++) {
+            if (__get_user(env->fpr[i], &frame->mc_fregs[i])) {
+                return 1;
+            }
+        }
+        if (__get_user(fpscr, &frame->mc_fregs[32]))
+            return 1;
+        env->fpscr = (uint32_t) fpscr;
+    }
+
+    /* Save SPE registers.  The kernel only saves the high half.  */
+    if (env->insns_flags & PPC_SPE) {
+#if defined(TARGET_PPC64)
+        for (i = 0; i < ARRAY_SIZE(env->gpr); i++) {
+            uint32_t hi;
+
+            if (__get_user(hi, &frame->mc_vregs.spe[i])) {
+                return 1;
+            }
+            env->gpr[i] = ((uint64_t)hi << 32) | ((uint32_t) env->gpr[i]);
+        }
+#else
+        for (i = 0; i < ARRAY_SIZE(env->gprh); i++) {
+            if (__get_user(env->gprh[i], &frame->mc_vregs.spe[i])) {
+                return 1;
+            }
+        }
+#endif
+        if (__get_user(env->spe_fscr, &frame->mc_vregs.spe[32]))
+            return 1;
+    }
+
+    return 0;
+}
+
+static void setup_frame(int sig, struct target_sigaction *ka,
+                        target_sigset_t *set, CPUState *env)
+{
+    struct target_sigframe *frame;
+    struct target_sigcontext *sc;
+    target_ulong frame_addr, newsp;
+    int err = 0;
+    int signal;
+
+    frame_addr = get_sigframe(ka, env, sizeof(*frame));
+    if (!lock_user_struct(VERIFY_WRITE, frame, frame_addr, 1))
+        goto sigsegv;
+    sc = &frame->sctx;
+
+    signal = current_exec_domain_sig(sig);
+
+    err |= __put_user(h2g(ka->_sa_handler), &sc->handler);
+    err |= __put_user(set->sig[0], &sc->oldmask);
+#if defined(TARGET_PPC64)
+    err |= __put_user(set->sig[0] >> 32, &sc->_unused[3]);
+#else
+    err |= __put_user(set->sig[1], &sc->_unused[3]);
+#endif
+    err |= __put_user(h2g(&frame->mctx), &sc->regs);
+    err |= __put_user(sig, &sc->signal);
+
+    /* Save user regs.  */
+    err |= save_user_regs(env, &frame->mctx, TARGET_NR_sigreturn);
+
+    /* The kernel checks for the presence of a VDSO here.  We don't
+       emulate a vdso, so use a sigreturn system call.  */
+    env->lr = (target_ulong) h2g(frame->mctx.tramp);
+
+    /* Turn off all fp exceptions.  */
+    env->fpscr = 0;
+
+    /* Create a stack frame for the caller of the handler.  */
+    newsp = frame_addr - SIGNAL_FRAMESIZE;
+    err |= __put_user(env->gpr[1], (target_ulong *)(uintptr_t) newsp);
+
+    if (err)
+        goto sigsegv;
+
+    /* Set up registers for signal handler.  */
+    env->gpr[1] = newsp;
+    env->gpr[3] = signal;
+    env->gpr[4] = (target_ulong) h2g(sc);
+    env->nip = (target_ulong) ka->_sa_handler;
+    /* Signal handlers are entered in big-endian mode.  */
+    env->msr &= ~MSR_LE;
+
+    unlock_user_struct(frame, frame_addr, 1);
+    return;
+
+sigsegv:
+    unlock_user_struct(frame, frame_addr, 1);
+    if (logfile)
+        fprintf (logfile, "segfaulting from setup_frame\n");
+    force_sig(SIGSEGV);
+}
+
+static void setup_rt_frame(int sig, struct target_sigaction *ka,
+                           target_siginfo_t *info,
+                           target_sigset_t *set, CPUState *env)
+{
+    struct target_rt_sigframe *rt_sf;
+    struct target_mcontext *frame;
+    target_ulong rt_sf_addr, newsp = 0;
+    int i, err = 0;
+    int signal;
+
+    rt_sf_addr = get_sigframe(ka, env, sizeof(*rt_sf));
+    if (!lock_user_struct(VERIFY_WRITE, rt_sf, rt_sf_addr, 1))
+        goto sigsegv;
+
+    signal = current_exec_domain_sig(sig);
+
+    err |= copy_siginfo_to_user(&rt_sf->info, info);
+
+    err |= __put_user(0, &rt_sf->uc.uc_flags);
+    err |= __put_user(0, &rt_sf->uc.uc_link);
+    err |= __put_user((target_ulong)target_sigaltstack_used.ss_sp,
+                      &rt_sf->uc.uc_stack.ss_sp);
+    err |= __put_user(sas_ss_flags(env->gpr[1]),
+                      &rt_sf->uc.uc_stack.ss_flags);
+    err |= __put_user(target_sigaltstack_used.ss_size,
+                      &rt_sf->uc.uc_stack.ss_size);
+    err |= __put_user(h2g (&rt_sf->uc.uc_mcontext),
+                      &rt_sf->uc.uc_regs);
+    for(i = 0; i < TARGET_NSIG_WORDS; i++) {
+        err |= __put_user(set->sig[i], &rt_sf->uc.uc_sigmask.sig[i]);
+    }
+
+    frame = &rt_sf->uc.uc_mcontext;
+    err |= save_user_regs(env, frame, TARGET_NR_rt_sigreturn);
+
+    /* The kernel checks for the presence of a VDSO here.  We don't
+       emulate a vdso, so use a sigreturn system call.  */
+    env->lr = (target_ulong) h2g(frame->tramp);
+
+    /* Turn off all fp exceptions.  */
+    env->fpscr = 0;
+
+    /* Create a stack frame for the caller of the handler.  */
+    newsp = rt_sf_addr - (SIGNAL_FRAMESIZE + 16);
+    err |= __put_user(env->gpr[1], (target_ulong *)(uintptr_t) newsp);
+
+    if (err)
+        goto sigsegv;
+
+    /* Set up registers for signal handler.  */
+    env->gpr[1] = newsp;
+    env->gpr[3] = (target_ulong) signal;
+    env->gpr[4] = (target_ulong) h2g(&rt_sf->info);
+    env->gpr[5] = (target_ulong) h2g(&rt_sf->uc);
+    env->gpr[6] = (target_ulong) h2g(rt_sf);
+    env->nip = (target_ulong) ka->_sa_handler;
+    /* Signal handlers are entered in big-endian mode.  */
+    env->msr &= ~MSR_LE;
+
+    unlock_user_struct(rt_sf, rt_sf_addr, 1);
+    return;
+
+sigsegv:
+    unlock_user_struct(rt_sf, rt_sf_addr, 1);
+    if (logfile)
+        fprintf (logfile, "segfaulting from setup_rt_frame\n");
+    force_sig(SIGSEGV);
+
+}
+
+long do_sigreturn(CPUState *env)
+{
+    struct target_sigcontext *sc = NULL;
+    struct target_mcontext *sr = NULL;
+    target_ulong sr_addr, sc_addr;
+    sigset_t blocked;
+    target_sigset_t set;
+
+    sc_addr = env->gpr[1] + SIGNAL_FRAMESIZE;
+    if (!lock_user_struct(VERIFY_READ, sc, sc_addr, 1))
+        goto sigsegv;
+
+#if defined(TARGET_PPC64)
+    set.sig[0] = sc->oldmask + ((long)(sc->_unused[3]) << 32);
+#else
+    if(__get_user(set.sig[0], &sc->oldmask) ||
+       __get_user(set.sig[1], &sc->_unused[3]))
+       goto sigsegv;
+#endif
+    target_to_host_sigset_internal(&blocked, &set);
+    sigprocmask(SIG_SETMASK, &blocked, NULL);
+
+    if (__get_user(sr_addr, &sc->regs))
+        goto sigsegv;
+    if (!lock_user_struct(VERIFY_READ, sr, sr_addr, 1))
+        goto sigsegv;
+    if (restore_user_regs(env, sr, 1))
+        goto sigsegv;
+
+    unlock_user_struct(sr, sr_addr, 1);
+    unlock_user_struct(sc, sc_addr, 1);
+    return -TARGET_QEMU_ESIGRETURN;
+
+sigsegv:
+    unlock_user_struct(sr, sr_addr, 1);
+    unlock_user_struct(sc, sc_addr, 1);
+    if (logfile)
+        fprintf (logfile, "segfaulting from do_sigreturn\n");
+    force_sig(SIGSEGV);
+    return 0;
+}
+
+/* See arch/powerpc/kernel/signal_32.c.  */
+static int do_setcontext(struct target_ucontext *ucp, CPUState *env, int sig)
+{
+    struct target_mcontext *mcp;
+    target_ulong mcp_addr;
+    sigset_t blocked;
+    target_sigset_t set;
+
+    if (copy_from_user(&set, h2g(ucp) + offsetof(struct target_ucontext, uc_sigmask),
+                       sizeof (set)))
+        return 1;
+
+#if defined(TARGET_PPC64)
+    fprintf (stderr, "do_setcontext: not implemented\n");
+    return 0;
+#else
+    if (__get_user(mcp_addr, &ucp->uc_regs))
+        return 1;
+
+    if (!lock_user_struct(VERIFY_READ, mcp, mcp_addr, 1))
+        return 1;
+
+    target_to_host_sigset_internal(&blocked, &set);
+    sigprocmask(SIG_SETMASK, &blocked, NULL);
+    if (restore_user_regs(env, mcp, sig))
+        goto sigsegv;
+
+    unlock_user_struct(mcp, mcp_addr, 1);
+    return 0;
+
+sigsegv:
+    unlock_user_struct(mcp, mcp_addr, 1);
+    return 1;
+#endif
+}
+
+long do_rt_sigreturn(CPUState *env)
+{
+    struct target_rt_sigframe *rt_sf = NULL;
+    target_ulong rt_sf_addr;
+
+    rt_sf_addr = env->gpr[1] + SIGNAL_FRAMESIZE + 16;
+    if (!lock_user_struct(VERIFY_READ, rt_sf, rt_sf_addr, 1))
+        goto sigsegv;
+
+    if (do_setcontext(&rt_sf->uc, env, 1))
+        goto sigsegv;
+
+    do_sigaltstack(rt_sf_addr
+                   + offsetof(struct target_rt_sigframe, uc.uc_stack),
+                   0, env->gpr[1]);
+
+    unlock_user_struct(rt_sf, rt_sf_addr, 1);
+    return -TARGET_QEMU_ESIGRETURN;
+
+sigsegv:
+    unlock_user_struct(rt_sf, rt_sf_addr, 1);
+    if (logfile)
+        fprintf (logfile, "segfaulting from do_rt_sigreturn\n");
+    force_sig(SIGSEGV);
+    return 0;
+}
+
 #else
 
 static void setup_frame(int sig, struct target_sigaction *ka,
-- 
1.6.0.5