target/xtensa: support output to chardev console

In semihosting mode QEMU allows guest to read and write host file
descriptors directly, including descriptors 0..2, a.k.a. stdin, stdout
and stderr. Sometimes it's desirable to have semihosting console
controlled by -serial option, e.g. to connect it to network.

Add semihosting console to xtensa-semi.c, open it in the 'sim' machine
in the presence of -serial option and direct stdout and stderr to it
when it's present.
Signed-off-by: NMax Filippov <jcmvbkbc@gmail.com>

hw/xtensa/sim.c

@@ -114,6 +114,9 @@ static void xtensa_sim_init(MachineState *machine)
         xtensa_create_memory_regions(&sysram, "xtensa.sysram");
     }
 
+    if (serial_hds[0]) {
+        xtensa_sim_open_console(serial_hds[0]);
+    }
     if (kernel_filename) {
         uint64_t elf_entry;
         uint64_t elf_lowaddr;
@@ -136,6 +139,7 @@ static void xtensa_sim_machine_init(MachineClass *mc)
     mc->is_default = true;
     mc->init = xtensa_sim_init;
     mc->max_cpus = 4;
+    mc->no_serial = 1;
 }
 
 DEFINE_MACHINE("sim", xtensa_sim_machine_init)

target/xtensa/cpu.h

@@ -483,6 +483,7 @@ void xtensa_translate_init(void);
 void xtensa_breakpoint_handler(CPUState *cs);
 void xtensa_finalize_config(XtensaConfig *config);
 void xtensa_register_core(XtensaConfigList *node);
+void xtensa_sim_open_console(Chardev *chr);
 void check_interrupts(CPUXtensaState *s);
 void xtensa_irq_init(CPUXtensaState *env);
 void *xtensa_get_extint(CPUXtensaState *env, unsigned extint);

target/xtensa/xtensa-semi.c

@@ -27,9 +27,14 @@
 
 #include "qemu/osdep.h"
 #include "cpu.h"
+#include "chardev/char-fe.h"
 #include "exec/helper-proto.h"
 #include "exec/semihost.h"
+#include "qapi/error.h"
 #include "qemu/log.h"
+#include "sysemu/sysemu.h"
+
+static CharBackend *xtensa_sim_console;
 
 enum {
     TARGET_SYS_exit = 1,
@@ -148,6 +153,15 @@ static uint32_t errno_h2g(int host_errno)
     }
 }
 
+void xtensa_sim_open_console(Chardev *chr)
+{
+    static CharBackend console;
+
+    qemu_chr_fe_init(&console, chr, &error_abort);
+    qemu_chr_fe_set_handlers(&console, NULL, NULL, NULL, NULL, NULL, true);
+    xtensa_sim_console = &console;
+}
+
 void HELPER(simcall)(CPUXtensaState *env)
 {
     CPUState *cs = CPU(xtensa_env_get_cpu(env));
@@ -181,10 +195,25 @@ void HELPER(simcall)(CPUXtensaState *env)
                 if (buf) {
                     vaddr += io_sz;
                     len -= io_sz;
+                    if (fd < 3 && xtensa_sim_console) {
+                        if (is_write && (fd == 1 || fd == 2)) {
+                            io_done = qemu_chr_fe_write_all(xtensa_sim_console,
+                                                            buf, io_sz);
+                            regs[3] = errno_h2g(errno);
+                        } else {
+                            qemu_log_mask(LOG_GUEST_ERROR,
+                                          "%s fd %d is not supported with chardev console\n",
+                                          is_write ?
+                                          "writing to" : "reading from", fd);
+                            io_done = -1;
+                            regs[3] = TARGET_EBADF;
+                        }
+                    } else {
                         io_done = is_write ?
                             write(fd, buf, io_sz) :
                             read(fd, buf, io_sz);
                         regs[3] = errno_h2g(errno);
+                    }
                     if (io_done == -1) {
                         error = true;
                         io_done = 0;
@@ -256,10 +285,6 @@ void HELPER(simcall)(CPUXtensaState *env)
             uint32_t target_tvv[2];
 
             struct timeval tv = {0};
-            fd_set fdset;
-
-            FD_ZERO(&fdset);
-            FD_SET(fd, &fdset);
 
             if (target_tv) {
                 cpu_memory_rw_debug(cs, target_tv,
@@ -267,6 +292,18 @@ void HELPER(simcall)(CPUXtensaState *env)
                 tv.tv_sec = (int32_t)tswap32(target_tvv[0]);
                 tv.tv_usec = (int32_t)tswap32(target_tvv[1]);
             }
+            if (fd < 3 && xtensa_sim_console) {
+                if ((fd == 1 || fd == 2) && rq == SELECT_ONE_WRITE) {
+                    regs[2] = 1;
+                } else {
+                    regs[2] = 0;
+                }
+                regs[3] = 0;
+            } else {
+                fd_set fdset;
+
+                FD_ZERO(&fdset);
+                FD_SET(fd, &fdset);
                 regs[2] = select(fd + 1,
                                  rq == SELECT_ONE_READ   ? &fdset : NULL,
                                  rq == SELECT_ONE_WRITE  ? &fdset : NULL,
@@ -274,6 +311,7 @@ void HELPER(simcall)(CPUXtensaState *env)
                                  target_tv ? &tv : NULL);
                 regs[3] = errno_h2g(errno);
             }
+        }
         break;
 
     case TARGET_SYS_argc: