target/xtensa: linux-user: add call0 ABI support

Xtensa binaries built for call0 ABI don't rotate register window on
function calls and returns. Invocation of signal handlers from the
kernel is therefore different in windowed and call0 ABIs.
There's currently no way to determine xtensa ELF binary ABI from the
binary itself. Add handler for the -xtensa-abi-call0 command line
parameter/QEMU_XTENSA_ABI_CALL0 envitonment variable to the qemu-user
and record ABI choice. Use it to initialize PS.WOE in xtensa_cpu_reset.
Check PS.WOE in setup_rt_frame to determine how a signal should be
delivered.

Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Message-Id: <20190906165713.5558-1-jcmvbkbc@gmail.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

linux-user/main.c

@@ -391,6 +391,13 @@ static void handle_arg_trace(const char *arg)
     trace_file = trace_opt_parse(arg);
 }
 
+#if defined(TARGET_XTENSA)
+static void handle_arg_abi_call0(const char *arg)
+{
+    xtensa_set_abi_call0();
+}
+#endif
+
 struct qemu_argument {
     const char *argv;
     const char *env;
@@ -444,6 +451,10 @@ static const struct qemu_argument arg_table[] = {
      "",           "[[enable=]<pattern>][,events=<file>][,file=<file>]"},
     {"version",    "QEMU_VERSION",     false, handle_arg_version,
      "",           "display version information and exit"},
+#if defined(TARGET_XTENSA)
+    {"xtensa-abi-call0", "QEMU_XTENSA_ABI_CALL0", false, handle_arg_abi_call0,
+     "",           "assume CALL0 Xtensa ABI"},
+#endif
     {NULL, NULL, false, NULL, NULL, NULL}
 };
 

linux-user/xtensa/signal.c

@@ -134,6 +134,8 @@ void setup_rt_frame(int sig, struct target_sigaction *ka,
     abi_ulong frame_addr;
     struct target_rt_sigframe *frame;
     uint32_t ra;
+    bool abi_call0;
+    unsigned base;
     int i;
 
     frame_addr = get_sigframe(ka, env, sizeof(*frame));
@@ -182,20 +184,27 @@ void setup_rt_frame(int sig, struct target_sigaction *ka,
         __put_user(0x00, &frame->retcode[5]);
 #endif
     }
-    env->sregs[PS] = PS_UM | (3 << PS_RING_SHIFT);
-    if (xtensa_option_enabled(env->config, XTENSA_OPTION_WINDOWED_REGISTER)) {
-        env->sregs[PS] |= PS_WOE | (1 << PS_CALLINC_SHIFT);
-    }
     memset(env->regs, 0, sizeof(env->regs));
     env->pc = ka->_sa_handler;
     env->regs[1] = frame_addr;
     env->sregs[WINDOW_BASE] = 0;
     env->sregs[WINDOW_START] = 1;
 
-    env->regs[4] = (ra & 0x3fffffff) | 0x40000000;
-    env->regs[6] = sig;
-    env->regs[7] = frame_addr + offsetof(struct target_rt_sigframe, info);
-    env->regs[8] = frame_addr + offsetof(struct target_rt_sigframe, uc);
+    abi_call0 = (env->sregs[PS] & PS_WOE) == 0;
+    env->sregs[PS] = PS_UM | (3 << PS_RING_SHIFT);
+
+    if (abi_call0) {
+        base = 0;
+        env->regs[base] = ra;
+    } else {
+        env->sregs[PS] |= PS_WOE | (1 << PS_CALLINC_SHIFT);
+        base = 4;
+        env->regs[base] = (ra & 0x3fffffff) | 0x40000000;
+    }
+    env->regs[base + 2] = sig;
+    env->regs[base + 3] = frame_addr + offsetof(struct target_rt_sigframe,
+                                                info);
+    env->regs[base + 4] = frame_addr + offsetof(struct target_rt_sigframe, uc);
     unlock_user_struct(frame, frame_addr, 1);
     return;
 

target/xtensa/cpu.c

@@ -53,6 +53,20 @@ static bool xtensa_cpu_has_work(CPUState *cs)
 #endif
 }
 
+#ifdef CONFIG_USER_ONLY
+static bool abi_call0;
+
+void xtensa_set_abi_call0(void)
+{
+    abi_call0 = true;
+}
+
+bool xtensa_abi_call0(void)
+{
+    return abi_call0;
+}
+#endif
+
 /* CPUClass::reset() */
 static void xtensa_cpu_reset(CPUState *s)
 {
@@ -70,10 +84,12 @@ static void xtensa_cpu_reset(CPUState *s)
             XTENSA_OPTION_INTERRUPT) ? 0x1f : 0x10;
     env->pending_irq_level = 0;
 #else
-    env->sregs[PS] =
-        (xtensa_option_enabled(env->config,
-                               XTENSA_OPTION_WINDOWED_REGISTER) ? PS_WOE : 0) |
-        PS_UM | (3 << PS_RING_SHIFT);
+    env->sregs[PS] = PS_UM | (3 << PS_RING_SHIFT);
+    if (xtensa_option_enabled(env->config,
+                              XTENSA_OPTION_WINDOWED_REGISTER) &&
+        !xtensa_abi_call0()) {
+        env->sregs[PS] |= PS_WOE;
+    }
 #endif
     env->sregs[VECBASE] = env->config->vecbase;
     env->sregs[IBREAKENABLE] = 0;

target/xtensa/cpu.h

@@ -673,6 +673,9 @@ static inline MemoryRegion *xtensa_get_er_region(CPUXtensaState *env)
 {
     return env->system_er;
 }
+#else
+void xtensa_set_abi_call0(void);
+bool xtensa_abi_call0(void);
 #endif
 
 static inline uint32_t xtensa_replicate_windowstart(CPUXtensaState *env)