linux-user: xtensa: fix signal delivery in FDPIC

In FDPIC signal handlers are passed around as FD pointers. Actual code
address and GOT pointer must be fetched from memory by the QEMU code
that implements kernel signal delivery functionality. This change is
equivalent to the following kernel change:
9c2cc74fb31e ("xtensa: fix signal delivery to FDPIC process")

Cc: qemu-stable@nongnu.org
Fixes: d2796be ("linux-user: add support for xtensa FDPIC")
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
(cherry picked from commit 1b173d0)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

linux-user/xtensa/signal.c

@@ -157,6 +157,9 @@ void setup_rt_frame(int sig, struct target_sigaction *ka,
 {
     abi_ulong frame_addr;
     struct target_rt_sigframe *frame;
+    int is_fdpic = info_is_fdpic(((TaskState *)thread_cpu->opaque)->info);
+    abi_ulong handler = 0;
+    abi_ulong handler_fdpic_GOT = 0;
     uint32_t ra;
     bool abi_call0;
     unsigned base;
@@ -165,6 +168,17 @@ void setup_rt_frame(int sig, struct target_sigaction *ka,
     frame_addr = get_sigframe(ka, env, sizeof(*frame));
     trace_user_setup_rt_frame(env, frame_addr);
 
+    if (is_fdpic) {
+        abi_ulong funcdesc_ptr = ka->_sa_handler;
+
+        if (get_user_ual(handler, funcdesc_ptr)
+            || get_user_ual(handler_fdpic_GOT, funcdesc_ptr + 4)) {
+            goto give_sigsegv;
+        }
+    } else {
+        handler = ka->_sa_handler;
+    }
+
     if (!lock_user_struct(VERIFY_WRITE, frame, frame_addr, 0)) {
         goto give_sigsegv;
     }
@@ -185,14 +199,21 @@ void setup_rt_frame(int sig, struct target_sigaction *ka,
     }
 
     if (ka->sa_flags & TARGET_SA_RESTORER) {
-        ra = ka->sa_restorer;
+        if (is_fdpic) {
+            if (get_user_ual(ra, ka->sa_restorer)) {
+                unlock_user_struct(frame, frame_addr, 0);
+                goto give_sigsegv;
+            }
+        } else {
+            ra = ka->sa_restorer;
+        }
     } else {
         /* Not used, but retain for ABI compatibility. */
         install_sigtramp(frame->retcode);
         ra = default_rt_sigreturn;
     }
     memset(env->regs, 0, sizeof(env->regs));
-    env->pc = ka->_sa_handler;
+    env->pc = handler;
     env->regs[1] = frame_addr;
     env->sregs[WINDOW_BASE] = 0;
     env->sregs[WINDOW_START] = 1;
@@ -212,6 +233,9 @@ void setup_rt_frame(int sig, struct target_sigaction *ka,
     env->regs[base + 3] = frame_addr + offsetof(struct target_rt_sigframe,
                                                 info);
     env->regs[base + 4] = frame_addr + offsetof(struct target_rt_sigframe, uc);
+    if (is_fdpic) {
+        env->regs[base + 11] = handler_fdpic_GOT;
+    }
     unlock_user_struct(frame, frame_addr, 1);
     return;