[Qemu-devel] [PATCH] target/xtensa: linux-user: add call0 ABI support

[Max Filippov <jcmvbkbc@gmail.com>]

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. Provide an environment variable QEMU_XTENSA_ABI_CALL0 and
use it to initialize PS.WOE in xtensa_cpu_reset. Check this flag in
setup_rt_frame to determine how a signal should be delivered.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
---
 linux-user/xtensa/signal.c | 25 +++++++++++++++++--------
 target/xtensa/cpu.c        | 22 ++++++++++++++++++----
 2 files changed, 35 insertions(+), 12 deletions(-)

diff --git a/linux-user/xtensa/signal.c b/linux-user/xtensa/signal.c
index 8d54ef3ae34b..590f0313ffe9 100644
--- a/linux-user/xtensa/signal.c
+++ b/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;
 
diff --git a/target/xtensa/cpu.c b/target/xtensa/cpu.c
index 76db1741a796..791c061880e7 100644
--- a/target/xtensa/cpu.c
+++ b/target/xtensa/cpu.c
@@ -53,6 +53,18 @@ static bool xtensa_cpu_has_work(CPUState *cs)
 #endif
 }
 
+#ifdef CONFIG_USER_ONLY
+static int xtensa_abi_call0(void)
+{
+    static int abi_call0 = -1;
+
+    if (abi_call0 == -1) {
+        abi_call0 = getenv("QEMU_XTENSA_ABI_CALL0") != NULL;
+    }
+    return abi_call0;
+}
+#endif
+
 /* CPUClass::reset() */
 static void xtensa_cpu_reset(CPUState *s)
 {
@@ -70,10 +82,12 @@ 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;
-- 
2.11.0