semihosting: Move ARM semihosting code to shared directories

This commit renames two files which provide ARM semihosting support so
that they can be shared by other architectures:

 1. target/arm/arm-semi.c     -> hw/semihosting/common-semi.c
 2. linux-user/arm/semihost.c -> linux-user/semihost.c

The build system was modified use a new config variable,
CONFIG_ARM_COMPATIBLE_SEMIHOSTING, which has been added to the ARM
softmmu and linux-user default configs. The contents of the source
files has not been changed in this patch.

Signed-off-by: Keith Packard <keithp@keithp.com>
[AJB: rename arm-compat-semi, select SEMIHOSTING]
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20210107170717.2098982-2-keithp@keithp.com>
Message-Id: <20210108224256.2321-13-alex.bennee@linaro.org>

3 files changed, 1128 insertions, 0 deletions

diff --git a/hw/semihosting/Kconfig b/hw/semihosting/Kconfig
index efe0a30734..eaf3a20ef5 100644
--- a/hw/semihosting/Kconfig
+++ b/hw/semihosting/Kconfig
@@ -1,3 +1,7 @@
 
 config SEMIHOSTING
        bool
+
+config ARM_COMPATIBLE_SEMIHOSTING
+       bool
+       select SEMIHOSTING
diff --git a/hw/semihosting/arm-compat-semi.c b/hw/semihosting/arm-compat-semi.c
new file mode 100644
index 0000000000..93360e28c7
--- /dev/null
+++ b/hw/semihosting/arm-compat-semi.c
@@ -0,0 +1,1121 @@
+/*
+ *  Arm "Angel" semihosting syscalls
+ *
+ *  Copyright (c) 2005, 2007 CodeSourcery.
+ *  Copyright (c) 2019 Linaro
+ *  Written by Paul Brook.
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program; if not, see <http://www.gnu.org/licenses/>.
+ *
+ *  ARM Semihosting is documented in:
+ *     Semihosting for AArch32 and AArch64 Release 2.0
+ *     https://static.docs.arm.com/100863/0200/semihosting.pdf
+ */
+
+#include "qemu/osdep.h"
+
+#include "cpu.h"
+#include "hw/semihosting/semihost.h"
+#include "hw/semihosting/console.h"
+#include "qemu/log.h"
+#ifdef CONFIG_USER_ONLY
+#include "qemu.h"
+
+#define ARM_ANGEL_HEAP_SIZE (128 * 1024 * 1024)
+#else
+#include "exec/gdbstub.h"
+#include "qemu/cutils.h"
+#include "hw/arm/boot.h"
+#include "hw/boards.h"
+#endif
+
+#define TARGET_SYS_OPEN        0x01
+#define TARGET_SYS_CLOSE       0x02
+#define TARGET_SYS_WRITEC      0x03
+#define TARGET_SYS_WRITE0      0x04
+#define TARGET_SYS_WRITE       0x05
+#define TARGET_SYS_READ        0x06
+#define TARGET_SYS_READC       0x07
+#define TARGET_SYS_ISTTY       0x09
+#define TARGET_SYS_SEEK        0x0a
+#define TARGET_SYS_FLEN        0x0c
+#define TARGET_SYS_TMPNAM      0x0d
+#define TARGET_SYS_REMOVE      0x0e
+#define TARGET_SYS_RENAME      0x0f
+#define TARGET_SYS_CLOCK       0x10
+#define TARGET_SYS_TIME        0x11
+#define TARGET_SYS_SYSTEM      0x12
+#define TARGET_SYS_ERRNO       0x13
+#define TARGET_SYS_GET_CMDLINE 0x15
+#define TARGET_SYS_HEAPINFO    0x16
+#define TARGET_SYS_EXIT        0x18
+#define TARGET_SYS_SYNCCACHE   0x19
+#define TARGET_SYS_EXIT_EXTENDED 0x20
+
+/* ADP_Stopped_ApplicationExit is used for exit(0),
+ * anything else is implemented as exit(1) */
+#define ADP_Stopped_ApplicationExit     (0x20026)
+
+#ifndef O_BINARY
+#define O_BINARY 0
+#endif
+
+#define GDB_O_RDONLY  0x000
+#define GDB_O_WRONLY  0x001
+#define GDB_O_RDWR    0x002
+#define GDB_O_APPEND  0x008
+#define GDB_O_CREAT   0x200
+#define GDB_O_TRUNC   0x400
+#define GDB_O_BINARY  0
+
+static int gdb_open_modeflags[12] = {
+    GDB_O_RDONLY,
+    GDB_O_RDONLY | GDB_O_BINARY,
+    GDB_O_RDWR,
+    GDB_O_RDWR | GDB_O_BINARY,
+    GDB_O_WRONLY | GDB_O_CREAT | GDB_O_TRUNC,
+    GDB_O_WRONLY | GDB_O_CREAT | GDB_O_TRUNC | GDB_O_BINARY,
+    GDB_O_RDWR | GDB_O_CREAT | GDB_O_TRUNC,
+    GDB_O_RDWR | GDB_O_CREAT | GDB_O_TRUNC | GDB_O_BINARY,
+    GDB_O_WRONLY | GDB_O_CREAT | GDB_O_APPEND,
+    GDB_O_WRONLY | GDB_O_CREAT | GDB_O_APPEND | GDB_O_BINARY,
+    GDB_O_RDWR | GDB_O_CREAT | GDB_O_APPEND,
+    GDB_O_RDWR | GDB_O_CREAT | GDB_O_APPEND | GDB_O_BINARY
+};
+
+static int open_modeflags[12] = {
+    O_RDONLY,
+    O_RDONLY | O_BINARY,
+    O_RDWR,
+    O_RDWR | O_BINARY,
+    O_WRONLY | O_CREAT | O_TRUNC,
+    O_WRONLY | O_CREAT | O_TRUNC | O_BINARY,
+    O_RDWR | O_CREAT | O_TRUNC,
+    O_RDWR | O_CREAT | O_TRUNC | O_BINARY,
+    O_WRONLY | O_CREAT | O_APPEND,
+    O_WRONLY | O_CREAT | O_APPEND | O_BINARY,
+    O_RDWR | O_CREAT | O_APPEND,
+    O_RDWR | O_CREAT | O_APPEND | O_BINARY
+};
+
+typedef enum GuestFDType {
+    GuestFDUnused = 0,
+    GuestFDHost = 1,
+    GuestFDGDB = 2,
+    GuestFDFeatureFile = 3,
+} GuestFDType;
+
+/*
+ * Guest file descriptors are integer indexes into an array of
+ * these structures (we will dynamically resize as necessary).
+ */
+typedef struct GuestFD {
+    GuestFDType type;
+    union {
+        int hostfd;
+        target_ulong featurefile_offset;
+    };
+} GuestFD;
+
+static GArray *guestfd_array;
+
+/*
+ * Allocate a new guest file descriptor and return it; if we
+ * couldn't allocate a new fd then return -1.
+ * This is a fairly simplistic implementation because we don't
+ * expect that most semihosting guest programs will make very
+ * heavy use of opening and closing fds.
+ */
+static int alloc_guestfd(void)
+{
+    guint i;
+
+    if (!guestfd_array) {
+        /* New entries zero-initialized, i.e. type GuestFDUnused */
+        guestfd_array = g_array_new(FALSE, TRUE, sizeof(GuestFD));
+    }
+
+    /* SYS_OPEN should return nonzero handle on success. Start guestfd from 1 */
+    for (i = 1; i < guestfd_array->len; i++) {
+        GuestFD *gf = &g_array_index(guestfd_array, GuestFD, i);
+
+        if (gf->type == GuestFDUnused) {
+            return i;
+        }
+    }
+
+    /* All elements already in use: expand the array */
+    g_array_set_size(guestfd_array, i + 1);
+    return i;
+}
+
+/*
+ * Look up the guestfd in the data structure; return NULL
+ * for out of bounds, but don't check whether the slot is unused.
+ * This is used internally by the other guestfd functions.
+ */
+static GuestFD *do_get_guestfd(int guestfd)
+{
+    if (!guestfd_array) {
+        return NULL;
+    }
+
+    if (guestfd <= 0 || guestfd >= guestfd_array->len) {
+        return NULL;
+    }
+
+    return &g_array_index(guestfd_array, GuestFD, guestfd);
+}
+
+/*
+ * Associate the specified guest fd (which must have been
+ * allocated via alloc_fd() and not previously used) with
+ * the specified host/gdb fd.
+ */
+static void associate_guestfd(int guestfd, int hostfd)
+{
+    GuestFD *gf = do_get_guestfd(guestfd);
+
+    assert(gf);
+    gf->type = use_gdb_syscalls() ? GuestFDGDB : GuestFDHost;
+    gf->hostfd = hostfd;
+}
+
+/*
+ * Deallocate the specified guest file descriptor. This doesn't
+ * close the host fd, it merely undoes the work of alloc_fd().
+ */
+static void dealloc_guestfd(int guestfd)
+{
+    GuestFD *gf = do_get_guestfd(guestfd);
+
+    assert(gf);
+    gf->type = GuestFDUnused;
+}
+
+/*
+ * Given a guest file descriptor, get the associated struct.
+ * If the fd is not valid, return NULL. This is the function
+ * used by the various semihosting calls to validate a handle
+ * from the guest.
+ * Note: calling alloc_guestfd() or dealloc_guestfd() will
+ * invalidate any GuestFD* obtained by calling this function.
+ */
+static GuestFD *get_guestfd(int guestfd)
+{
+    GuestFD *gf = do_get_guestfd(guestfd);
+
+    if (!gf || gf->type == GuestFDUnused) {
+        return NULL;
+    }
+    return gf;
+}
+
+/*
+ * The semihosting API has no concept of its errno being thread-safe,
+ * as the API design predates SMP CPUs and was intended as a simple
+ * real-hardware set of debug functionality. For QEMU, we make the
+ * errno be per-thread in linux-user mode; in softmmu it is a simple
+ * global, and we assume that the guest takes care of avoiding any races.
+ */
+#ifndef CONFIG_USER_ONLY
+static target_ulong syscall_err;
+
+#include "exec/softmmu-semi.h"
+#endif
+
+static inline uint32_t set_swi_errno(CPUARMState *env, uint32_t code)
+{
+    if (code == (uint32_t)-1) {
+#ifdef CONFIG_USER_ONLY
+        CPUState *cs = env_cpu(env);
+        TaskState *ts = cs->opaque;
+
+        ts->swi_errno = errno;
+#else
+        syscall_err = errno;
+#endif
+    }
+    return code;
+}
+
+static inline uint32_t get_swi_errno(CPUARMState *env)
+{
+#ifdef CONFIG_USER_ONLY
+    CPUState *cs = env_cpu(env);
+    TaskState *ts = cs->opaque;
+
+    return ts->swi_errno;
+#else
+    return syscall_err;
+#endif
+}
+
+static target_ulong arm_semi_syscall_len;
+
+static void arm_semi_cb(CPUState *cs, target_ulong ret, target_ulong err)
+{
+    ARMCPU *cpu = ARM_CPU(cs);
+    CPUARMState *env = &cpu->env;
+    target_ulong reg0 = is_a64(env) ? env->xregs[0] : env->regs[0];
+
+    if (ret == (target_ulong)-1) {
+        errno = err;
+        set_swi_errno(env, -1);
+        reg0 = ret;
+    } else {
+        /* Fixup syscalls that use nonstardard return conventions.  */
+        switch (reg0) {
+        case TARGET_SYS_WRITE:
+        case TARGET_SYS_READ:
+            reg0 = arm_semi_syscall_len - ret;
+            break;
+        case TARGET_SYS_SEEK:
+            reg0 = 0;
+            break;
+        default:
+            reg0 = ret;
+            break;
+        }
+    }
+    if (is_a64(env)) {
+        env->xregs[0] = reg0;
+    } else {
+        env->regs[0] = reg0;
+    }
+}
+
+static target_ulong arm_flen_buf(ARMCPU *cpu)
+{
+    /* Return an address in target memory of 64 bytes where the remote
+     * gdb should write its stat struct. (The format of this structure
+     * is defined by GDB's remote protocol and is not target-specific.)
+     * We put this on the guest's stack just below SP.
+     */
+    CPUARMState *env = &cpu->env;
+    target_ulong sp;
+
+    if (is_a64(env)) {
+        sp = env->xregs[31];
+    } else {
+        sp = env->regs[13];
+    }
+
+    return sp - 64;
+}
+
+static void arm_semi_flen_cb(CPUState *cs, target_ulong ret, target_ulong err)
+{
+    ARMCPU *cpu = ARM_CPU(cs);
+    CPUARMState *env = &cpu->env;
+    /* The size is always stored in big-endian order, extract
+       the value. We assume the size always fit in 32 bits.  */
+    uint32_t size;
+    cpu_memory_rw_debug(cs, arm_flen_buf(cpu) + 32, (uint8_t *)&size, 4, 0);
+    size = be32_to_cpu(size);
+    if (is_a64(env)) {
+        env->xregs[0] = size;
+    } else {
+        env->regs[0] = size;
+    }
+    errno = err;
+    set_swi_errno(env, -1);
+}
+
+static int arm_semi_open_guestfd;
+
+static void arm_semi_open_cb(CPUState *cs, target_ulong ret, target_ulong err)
+{
+    ARMCPU *cpu = ARM_CPU(cs);
+    CPUARMState *env = &cpu->env;
+    if (ret == (target_ulong)-1) {
+        errno = err;
+        set_swi_errno(env, -1);
+        dealloc_guestfd(arm_semi_open_guestfd);
+    } else {
+        associate_guestfd(arm_semi_open_guestfd, ret);
+        ret = arm_semi_open_guestfd;
+    }
+
+    if (is_a64(env)) {
+        env->xregs[0] = ret;
+    } else {
+        env->regs[0] = ret;
+    }
+}
+
+static target_ulong arm_gdb_syscall(ARMCPU *cpu, gdb_syscall_complete_cb cb,
+                                    const char *fmt, ...)
+{
+    va_list va;
+    CPUARMState *env = &cpu->env;
+
+    va_start(va, fmt);
+    gdb_do_syscallv(cb, fmt, va);
+    va_end(va);
+
+    /*
+     * FIXME: in softmmu mode, the gdbstub will schedule our callback
+     * to occur, but will not actually call it to complete the syscall
+     * until after this function has returned and we are back in the
+     * CPU main loop. Therefore callers to this function must not
+     * do anything with its return value, because it is not necessarily
+     * the result of the syscall, but could just be the old value of X0.
+     * The only thing safe to do with this is that the callers of
+     * do_arm_semihosting() will write it straight back into X0.
+     * (In linux-user mode, the callback will have happened before
+     * gdb_do_syscallv() returns.)
+     *
+     * We should tidy this up so neither this function nor
+     * do_arm_semihosting() return a value, so the mistake of
+     * doing something with the return value is not possible to make.
+     */
+
+    return is_a64(env) ? env->xregs[0] : env->regs[0];
+}
+
+/*
+ * Types for functions implementing various semihosting calls
+ * for specific types of guest file descriptor. These must all
+ * do the work and return the required return value for the guest,
+ * setting the guest errno if appropriate.
+ */
+typedef uint32_t sys_closefn(ARMCPU *cpu, GuestFD *gf);
+typedef uint32_t sys_writefn(ARMCPU *cpu, GuestFD *gf,
+                             target_ulong buf, uint32_t len);
+typedef uint32_t sys_readfn(ARMCPU *cpu, GuestFD *gf,
+                            target_ulong buf, uint32_t len);
+typedef uint32_t sys_isattyfn(ARMCPU *cpu, GuestFD *gf);
+typedef uint32_t sys_seekfn(ARMCPU *cpu, GuestFD *gf,
+                            target_ulong offset);
+typedef uint32_t sys_flenfn(ARMCPU *cpu, GuestFD *gf);
+
+static uint32_t host_closefn(ARMCPU *cpu, GuestFD *gf)
+{
+    CPUARMState *env = &cpu->env;
+
+    /*
+     * Only close the underlying host fd if it's one we opened on behalf
+     * of the guest in SYS_OPEN.
+     */
+    if (gf->hostfd == STDIN_FILENO ||
+        gf->hostfd == STDOUT_FILENO ||
+        gf->hostfd == STDERR_FILENO) {
+        return 0;
+    }
+    return set_swi_errno(env, close(gf->hostfd));
+}
+
+static uint32_t host_writefn(ARMCPU *cpu, GuestFD *gf,
+                             target_ulong buf, uint32_t len)
+{
+    uint32_t ret;
+    CPUARMState *env = &cpu->env;
+    char *s = lock_user(VERIFY_READ, buf, len, 1);
+    if (!s) {
+        /* Return bytes not written on error */
+        return len;
+    }
+    ret = set_swi_errno(env, write(gf->hostfd, s, len));
+    unlock_user(s, buf, 0);
+    if (ret == (uint32_t)-1) {
+        ret = 0;
+    }
+    /* Return bytes not written */
+    return len - ret;
+}
+
+static uint32_t host_readfn(ARMCPU *cpu, GuestFD *gf,
+                            target_ulong buf, uint32_t len)
+{
+    uint32_t ret;
+    CPUARMState *env = &cpu->env;
+    char *s = lock_user(VERIFY_WRITE, buf, len, 0);
+    if (!s) {
+        /* return bytes not read */
+        return len;
+    }
+    do {
+        ret = set_swi_errno(env, read(gf->hostfd, s, len));
+    } while (ret == -1 && errno == EINTR);
+    unlock_user(s, buf, len);
+    if (ret == (uint32_t)-1) {
+        ret = 0;
+    }
+    /* Return bytes not read */
+    return len - ret;
+}
+
+static uint32_t host_isattyfn(ARMCPU *cpu, GuestFD *gf)
+{
+    return isatty(gf->hostfd);
+}
+
+static uint32_t host_seekfn(ARMCPU *cpu, GuestFD *gf, target_ulong offset)
+{
+    CPUARMState *env = &cpu->env;
+    uint32_t ret = set_swi_errno(env, lseek(gf->hostfd, offset, SEEK_SET));
+    if (ret == (uint32_t)-1) {
+        return -1;
+    }
+    return 0;
+}
+
+static uint32_t host_flenfn(ARMCPU *cpu, GuestFD *gf)
+{
+    CPUARMState *env = &cpu->env;
+    struct stat buf;
+    uint32_t ret = set_swi_errno(env, fstat(gf->hostfd, &buf));
+    if (ret == (uint32_t)-1) {
+        return -1;
+    }
+    return buf.st_size;
+}
+
+static uint32_t gdb_closefn(ARMCPU *cpu, GuestFD *gf)
+{
+    return arm_gdb_syscall(cpu, arm_semi_cb, "close,%x", gf->hostfd);
+}
+
+static uint32_t gdb_writefn(ARMCPU *cpu, GuestFD *gf,
+                            target_ulong buf, uint32_t len)
+{
+    arm_semi_syscall_len = len;
+    return arm_gdb_syscall(cpu, arm_semi_cb, "write,%x,%x,%x",
+                           gf->hostfd, buf, len);
+}
+
+static uint32_t gdb_readfn(ARMCPU *cpu, GuestFD *gf,
+                           target_ulong buf, uint32_t len)
+{
+    arm_semi_syscall_len = len;
+    return arm_gdb_syscall(cpu, arm_semi_cb, "read,%x,%x,%x",
+                           gf->hostfd, buf, len);
+}
+
+static uint32_t gdb_isattyfn(ARMCPU *cpu, GuestFD *gf)
+{
+    return arm_gdb_syscall(cpu, arm_semi_cb, "isatty,%x", gf->hostfd);
+}
+
+static uint32_t gdb_seekfn(ARMCPU *cpu, GuestFD *gf, target_ulong offset)
+{
+    return arm_gdb_syscall(cpu, arm_semi_cb, "lseek,%x,%x,0",
+                           gf->hostfd, offset);
+}
+
+static uint32_t gdb_flenfn(ARMCPU *cpu, GuestFD *gf)
+{
+    return arm_gdb_syscall(cpu, arm_semi_flen_cb, "fstat,%x,%x",
+                           gf->hostfd, arm_flen_buf(cpu));
+}
+
+#define SHFB_MAGIC_0 0x53
+#define SHFB_MAGIC_1 0x48
+#define SHFB_MAGIC_2 0x46
+#define SHFB_MAGIC_3 0x42
+
+/* Feature bits reportable in feature byte 0 */
+#define SH_EXT_EXIT_EXTENDED (1 << 0)
+#define SH_EXT_STDOUT_STDERR (1 << 1)
+
+static const uint8_t featurefile_data[] = {
+    SHFB_MAGIC_0,
+    SHFB_MAGIC_1,
+    SHFB_MAGIC_2,
+    SHFB_MAGIC_3,
+    SH_EXT_EXIT_EXTENDED | SH_EXT_STDOUT_STDERR, /* Feature byte 0 */
+};
+
+static void init_featurefile_guestfd(int guestfd)
+{
+    GuestFD *gf = do_get_guestfd(guestfd);
+
+    assert(gf);
+    gf->type = GuestFDFeatureFile;
+    gf->featurefile_offset = 0;
+}
+
+static uint32_t featurefile_closefn(ARMCPU *cpu, GuestFD *gf)
+{
+    /* Nothing to do */
+    return 0;
+}
+
+static uint32_t featurefile_writefn(ARMCPU *cpu, GuestFD *gf,
+                                    target_ulong buf, uint32_t len)
+{
+    /* This fd can never be open for writing */
+    CPUARMState *env = &cpu->env;
+
+    errno = EBADF;
+    return set_swi_errno(env, -1);
+}
+
+static uint32_t featurefile_readfn(ARMCPU *cpu, GuestFD *gf,
+                                   target_ulong buf, uint32_t len)
+{
+    uint32_t i;
+#ifndef CONFIG_USER_ONLY
+    CPUARMState *env = &cpu->env;
+#endif
+    char *s;
+
+    s = lock_user(VERIFY_WRITE, buf, len, 0);
+    if (!s) {
+        return len;
+    }
+
+    for (i = 0; i < len; i++) {
+        if (gf->featurefile_offset >= sizeof(featurefile_data)) {
+            break;
+        }
+        s[i] = featurefile_data[gf->featurefile_offset];
+        gf->featurefile_offset++;
+    }
+
+    unlock_user(s, buf, len);
+
+    /* Return number of bytes not read */
+    return len - i;
+}
+
+static uint32_t featurefile_isattyfn(ARMCPU *cpu, GuestFD *gf)
+{
+    return 0;
+}
+
+static uint32_t featurefile_seekfn(ARMCPU *cpu, GuestFD *gf,
+                                   target_ulong offset)
+{
+    gf->featurefile_offset = offset;
+    return 0;
+}
+
+static uint32_t featurefile_flenfn(ARMCPU *cpu, GuestFD *gf)
+{
+    return sizeof(featurefile_data);
+}
+
+typedef struct GuestFDFunctions {
+    sys_closefn *closefn;
+    sys_writefn *writefn;
+    sys_readfn *readfn;
+    sys_isattyfn *isattyfn;
+    sys_seekfn *seekfn;
+    sys_flenfn *flenfn;
+} GuestFDFunctions;
+
+static const GuestFDFunctions guestfd_fns[] = {
+    [GuestFDHost] = {
+        .closefn = host_closefn,
+        .writefn = host_writefn,
+        .readfn = host_readfn,
+        .isattyfn = host_isattyfn,
+        .seekfn = host_seekfn,
+        .flenfn = host_flenfn,
+    },
+    [GuestFDGDB] = {
+        .closefn = gdb_closefn,
+        .writefn = gdb_writefn,
+        .readfn = gdb_readfn,
+        .isattyfn = gdb_isattyfn,
+        .seekfn = gdb_seekfn,
+        .flenfn = gdb_flenfn,
+    },
+    [GuestFDFeatureFile] = {
+        .closefn = featurefile_closefn,
+        .writefn = featurefile_writefn,
+        .readfn = featurefile_readfn,
+        .isattyfn = featurefile_isattyfn,
+        .seekfn = featurefile_seekfn,
+        .flenfn = featurefile_flenfn,
+    },
+};
+
+/* Read the input value from the argument block; fail the semihosting
+ * call if the memory read fails.
+ */
+#define GET_ARG(n) do {                                 \
+    if (is_a64(env)) {                                  \
+        if (get_user_u64(arg ## n, args + (n) * 8)) {   \
+            errno = EFAULT;                             \
+            return set_swi_errno(env, -1);              \
+        }                                               \
+    } else {                                            \
+        if (get_user_u32(arg ## n, args + (n) * 4)) {   \
+            errno = EFAULT;                             \
+            return set_swi_errno(env, -1);              \
+        }                                               \
+    }                                                   \
+} while (0)
+
+#define SET_ARG(n, val)                                 \
+    (is_a64(env) ?                                      \
+     put_user_u64(val, args + (n) * 8) :                \
+     put_user_u32(val, args + (n) * 4))
+
+/*
+ * Do a semihosting call.
+ *
+ * The specification always says that the "return register" either
+ * returns a specific value or is corrupted, so we don't need to
+ * report to our caller whether we are returning a value or trying to
+ * leave the register unchanged. We use 0xdeadbeef as the return value
+ * when there isn't a defined return value for the call.
+ */
+target_ulong do_arm_semihosting(CPUARMState *env)
+{
+    ARMCPU *cpu = env_archcpu(env);
+    CPUState *cs = env_cpu(env);
+    target_ulong args;
+    target_ulong arg0, arg1, arg2, arg3;
+    char * s;
+    int nr;
+    uint32_t ret;
+    uint32_t len;
+    GuestFD *gf;
+
+    if (is_a64(env)) {
+        /* Note that the syscall number is in W0, not X0 */
+        nr = env->xregs[0] & 0xffffffffU;
+        args = env->xregs[1];
+    } else {
+        nr = env->regs[0];
+        args = env->regs[1];
+    }
+
+    switch (nr) {
+    case TARGET_SYS_OPEN:
+    {
+        int guestfd;
+
+        GET_ARG(0);
+        GET_ARG(1);
+        GET_ARG(2);
+        s = lock_user_string(arg0);
+        if (!s) {
+            errno = EFAULT;
+            return set_swi_errno(env, -1);
+        }
+        if (arg1 >= 12) {
+            unlock_user(s, arg0, 0);
+            errno = EINVAL;
+            return set_swi_errno(env, -1);
+        }
+
+        guestfd = alloc_guestfd();
+        if (guestfd < 0) {
+            unlock_user(s, arg0, 0);
+            errno = EMFILE;
+            return set_swi_errno(env, -1);
+        }
+
+        if (strcmp(s, ":tt") == 0) {
+            int result_fileno;
+
+            /*
+             * We implement SH_EXT_STDOUT_STDERR, so:
+             *  open for read == stdin
+             *  open for write == stdout
+             *  open for append == stderr
+             */
+            if (arg1 < 4) {
+                result_fileno = STDIN_FILENO;
+            } else if (arg1 < 8) {
+                result_fileno = STDOUT_FILENO;
+            } else {
+                result_fileno = STDERR_FILENO;
+            }
+            associate_guestfd(guestfd, result_fileno);
+            unlock_user(s, arg0, 0);
+            return guestfd;
+        }
+        if (strcmp(s, ":semihosting-features") == 0) {
+            unlock_user(s, arg0, 0);
+            /* We must fail opens for modes other than 0 ('r') or 1 ('rb') */
+            if (arg1 != 0 && arg1 != 1) {
+                dealloc_guestfd(guestfd);
+                errno = EACCES;
+                return set_swi_errno(env, -1);
+            }
+            init_featurefile_guestfd(guestfd);
+            return guestfd;
+        }
+
+        if (use_gdb_syscalls()) {
+            arm_semi_open_guestfd = guestfd;
+            ret = arm_gdb_syscall(cpu, arm_semi_open_cb, "open,%s,%x,1a4", arg0,
+                                  (int)arg2 + 1, gdb_open_modeflags[arg1]);
+        } else {
+            ret = set_swi_errno(env, open(s, open_modeflags[arg1], 0644));
+            if (ret == (uint32_t)-1) {
+                dealloc_guestfd(guestfd);
+            } else {
+                associate_guestfd(guestfd, ret);
+                ret = guestfd;
+            }
+        }
+        unlock_user(s, arg0, 0);
+        return ret;
+    }
+    case TARGET_SYS_CLOSE:
+        GET_ARG(0);
+
+        gf = get_guestfd(arg0);
+        if (!gf) {
+            errno = EBADF;
+            return set_swi_errno(env, -1);
+        }
+
+        ret = guestfd_fns[gf->type].closefn(cpu, gf);
+        dealloc_guestfd(arg0);
+        return ret;
+    case TARGET_SYS_WRITEC:
+        qemu_semihosting_console_outc(env, args);
+        return 0xdeadbeef;
+    case TARGET_SYS_WRITE0:
+        return qemu_semihosting_console_outs(env, args);
+    case TARGET_SYS_WRITE:
+        GET_ARG(0);
+        GET_ARG(1);
+        GET_ARG(2);
+        len = arg2;
+
+        gf = get_guestfd(arg0);
+        if (!gf) {
+            errno = EBADF;
+            return set_swi_errno(env, -1);
+        }
+
+        return guestfd_fns[gf->type].writefn(cpu, gf, arg1, len);
+    case TARGET_SYS_READ:
+        GET_ARG(0);
+        GET_ARG(1);
+        GET_ARG(2);
+        len = arg2;
+
+        gf = get_guestfd(arg0);
+        if (!gf) {
+            errno = EBADF;
+            return set_swi_errno(env, -1);
+        }
+
+        return guestfd_fns[gf->type].readfn(cpu, gf, arg1, len);
+    case TARGET_SYS_READC:
+        return qemu_semihosting_console_inc(env);
+    case TARGET_SYS_ISTTY:
+        GET_ARG(0);
+
+        gf = get_guestfd(arg0);
+        if (!gf) {
+            errno = EBADF;
+            return set_swi_errno(env, -1);
+        }
+
+        return guestfd_fns[gf->type].isattyfn(cpu, gf);
+    case TARGET_SYS_SEEK:
+        GET_ARG(0);
+        GET_ARG(1);
+
+        gf = get_guestfd(arg0);
+        if (!gf) {
+            errno = EBADF;
+            return set_swi_errno(env, -1);
+        }
+
+        return guestfd_fns[gf->type].seekfn(cpu, gf, arg1);
+    case TARGET_SYS_FLEN:
+        GET_ARG(0);
+
+        gf = get_guestfd(arg0);
+        if (!gf) {
+            errno = EBADF;
+            return set_swi_errno(env, -1);
+        }
+
+        return guestfd_fns[gf->type].flenfn(cpu, gf);
+    case TARGET_SYS_TMPNAM:
+        qemu_log_mask(LOG_UNIMP, "%s: SYS_TMPNAM not implemented", __func__);
+        return -1;
+    case TARGET_SYS_REMOVE:
+        GET_ARG(0);
+        GET_ARG(1);
+        if (use_gdb_syscalls()) {
+            ret = arm_gdb_syscall(cpu, arm_semi_cb, "unlink,%s",
+                                  arg0, (int)arg1 + 1);
+        } else {
+            s = lock_user_string(arg0);
+            if (!s) {
+                errno = EFAULT;
+                return set_swi_errno(env, -1);
+            }
+            ret =  set_swi_errno(env, remove(s));
+            unlock_user(s, arg0, 0);
+        }
+        return ret;
+    case TARGET_SYS_RENAME:
+        GET_ARG(0);
+        GET_ARG(1);
+        GET_ARG(2);
+        GET_ARG(3);
+        if (use_gdb_syscalls()) {
+            return arm_gdb_syscall(cpu, arm_semi_cb, "rename,%s,%s",
+                                   arg0, (int)arg1 + 1, arg2, (int)arg3 + 1);
+        } else {
+            char *s2;
+            s = lock_user_string(arg0);
+            s2 = lock_user_string(arg2);
+            if (!s || !s2) {
+                errno = EFAULT;
+                ret = set_swi_errno(env, -1);
+            } else {
+                ret = set_swi_errno(env, rename(s, s2));
+            }
+            if (s2)
+                unlock_user(s2, arg2, 0);
+            if (s)
+                unlock_user(s, arg0, 0);
+            return ret;
+        }
+    case TARGET_SYS_CLOCK:
+        return clock() / (CLOCKS_PER_SEC / 100);
+    case TARGET_SYS_TIME:
+        return set_swi_errno(env, time(NULL));
+    case TARGET_SYS_SYSTEM:
+        GET_ARG(0);
+        GET_ARG(1);
+        if (use_gdb_syscalls()) {
+            return arm_gdb_syscall(cpu, arm_semi_cb, "system,%s",
+                                   arg0, (int)arg1 + 1);
+        } else {
+            s = lock_user_string(arg0);
+            if (!s) {
+                errno = EFAULT;
+                return set_swi_errno(env, -1);
+            }
+            ret = set_swi_errno(env, system(s));
+            unlock_user(s, arg0, 0);
+            return ret;
+        }
+    case TARGET_SYS_ERRNO:
+        return get_swi_errno(env);
+    case TARGET_SYS_GET_CMDLINE:
+        {
+            /* Build a command-line from the original argv.
+             *
+             * The inputs are:
+             *     * arg0, pointer to a buffer of at least the size
+             *               specified in arg1.
+             *     * arg1, size of the buffer pointed to by arg0 in
+             *               bytes.
+             *
+             * The outputs are:
+             *     * arg0, pointer to null-terminated string of the
+             *               command line.
+             *     * arg1, length of the string pointed to by arg0.
+             */
+
+            char *output_buffer;
+            size_t input_size;
+            size_t output_size;
+            int status = 0;
+#if !defined(CONFIG_USER_ONLY)
+            const char *cmdline;
+#else
+            TaskState *ts = cs->opaque;
+#endif
+            GET_ARG(0);
+            GET_ARG(1);
+            input_size = arg1;
+            /* Compute the size of the output string.  */
+#if !defined(CONFIG_USER_ONLY)
+            cmdline = semihosting_get_cmdline();
+            if (cmdline == NULL) {
+                cmdline = ""; /* Default to an empty line. */
+            }
+            output_size = strlen(cmdline) + 1; /* Count terminating 0. */
+#else
+            unsigned int i;
+
+            output_size = ts->info->arg_end - ts->info->arg_start;
+            if (!output_size) {
+                /*
+                 * We special-case the "empty command line" case (argc==0).
+                 * Just provide the terminating 0.
+                 */
+                output_size = 1;
+            }
+#endif
+
+            if (output_size > input_size) {
+                /* Not enough space to store command-line arguments.  */
+                errno = E2BIG;
+                return set_swi_errno(env, -1);
+            }
+
+            /* Adjust the command-line length.  */
+            if (SET_ARG(1, output_size - 1)) {
+                /* Couldn't write back to argument block */
+                errno = EFAULT;
+                return set_swi_errno(env, -1);
+            }
+
+            /* Lock the buffer on the ARM side.  */
+            output_buffer = lock_user(VERIFY_WRITE, arg0, output_size, 0);
+            if (!output_buffer) {
+                errno = EFAULT;
+                return set_swi_errno(env, -1);
+            }
+
+            /* Copy the command-line arguments.  */
+#if !defined(CONFIG_USER_ONLY)
+            pstrcpy(output_buffer, output_size, cmdline);
+#else
+            if (output_size == 1) {
+                /* Empty command-line.  */
+                output_buffer[0] = '\0';
+                goto out;
+            }
+
+            if (copy_from_user(output_buffer, ts->info->arg_start,
+                               output_size)) {
+                errno = EFAULT;
+                status = set_swi_errno(env, -1);
+                goto out;
+            }
+
+            /* Separate arguments by white spaces.  */
+            for (i = 0; i < output_size - 1; i++) {
+                if (output_buffer[i] == 0) {
+                    output_buffer[i] = ' ';
+                }
+            }
+        out:
+#endif
+            /* Unlock the buffer on the ARM side.  */
+            unlock_user(output_buffer, arg0, output_size);
+
+            return status;
+        }
+    case TARGET_SYS_HEAPINFO:
+        {
+            target_ulong retvals[4];
+            target_ulong limit;
+            int i;
+#ifdef CONFIG_USER_ONLY
+            TaskState *ts = cs->opaque;
+#else
+            const struct arm_boot_info *info = env->boot_info;
+            target_ulong rambase = info->loader_start;
+#endif
+
+            GET_ARG(0);
+
+#ifdef CONFIG_USER_ONLY
+            /*
+             * Some C libraries assume the heap immediately follows .bss, so
+             * allocate it using sbrk.
+             */
+            if (!ts->heap_limit) {
+                abi_ulong ret;
+
+                ts->heap_base = do_brk(0);
+                limit = ts->heap_base + ARM_ANGEL_HEAP_SIZE;
+                /* Try a big heap, and reduce the size if that fails.  */
+                for (;;) {
+                    ret = do_brk(limit);
+                    if (ret >= limit) {
+                        break;
+                    }
+                    limit = (ts->heap_base >> 1) + (limit >> 1);
+                }
+                ts->heap_limit = limit;
+            }
+
+            retvals[0] = ts->heap_base;
+            retvals[1] = ts->heap_limit;
+            retvals[2] = ts->stack_base;
+            retvals[3] = 0; /* Stack limit.  */
+#else
+            limit = current_machine->ram_size;
+            /* TODO: Make this use the limit of the loaded application.  */
+            retvals[0] = rambase + limit / 2;
+            retvals[1] = rambase + limit;
+            retvals[2] = rambase + limit; /* Stack base */
+            retvals[3] = rambase; /* Stack limit.  */
+#endif
+
+            for (i = 0; i < ARRAY_SIZE(retvals); i++) {
+                bool fail;
+
+                if (is_a64(env)) {
+                    fail = put_user_u64(retvals[i], arg0 + i * 8);
+                } else {
+                    fail = put_user_u32(retvals[i], arg0 + i * 4);
+                }
+
+                if (fail) {
+                    /* Couldn't write back to argument block */
+                    errno = EFAULT;
+                    return set_swi_errno(env, -1);
+                }
+            }
+            return 0;
+        }
+    case TARGET_SYS_EXIT:
+    case TARGET_SYS_EXIT_EXTENDED:
+        if (nr == TARGET_SYS_EXIT_EXTENDED || is_a64(env)) {
+            /*
+             * The A64 version of SYS_EXIT takes a parameter block,
+             * so the application-exit type can return a subcode which
+             * is the exit status code from the application.
+             * SYS_EXIT_EXTENDED is an a new-in-v2.0 optional function
+             * which allows A32/T32 guests to also provide a status code.
+             */
+            GET_ARG(0);
+            GET_ARG(1);
+
+            if (arg0 == ADP_Stopped_ApplicationExit) {
+                ret = arg1;
+            } else {
+                ret = 1;
+            }
+        } else {
+            /*
+             * The A32/T32 version of SYS_EXIT specifies only
+             * Stopped_ApplicationExit as normal exit, but does not
+             * allow the guest to specify the exit status code.
+             * Everything else is considered an error.
+             */
+            ret = (args == ADP_Stopped_ApplicationExit) ? 0 : 1;
+        }
+        gdb_exit(ret);
+        exit(ret);
+    case TARGET_SYS_SYNCCACHE:
+        /*
+         * Clean the D-cache and invalidate the I-cache for the specified
+         * virtual address range. This is a nop for us since we don't
+         * implement caches. This is only present on A64.
+         */
+        if (is_a64(env)) {
+            return 0;
+        }
+        /* fall through -- invalid for A32/T32 */
+    default:
+        fprintf(stderr, "qemu: Unsupported SemiHosting SWI 0x%02x\n", nr);
+        cpu_dump_state(cs, stderr, 0);
+        abort();
+    }
+}
diff --git a/hw/semihosting/meson.build b/hw/semihosting/meson.build
index f40ac574c4..ea8090abe3 100644
--- a/hw/semihosting/meson.build
+++ b/hw/semihosting/meson.build
@@ -2,3 +2,6 @@ specific_ss.add(when: 'CONFIG_SEMIHOSTING', if_true: files(
   'config.c',
   'console.c',
 ))
+
+specific_ss.add(when: ['CONFIG_ARM_COMPATIBLE_SEMIHOSTING'],
+		if_true: files('arm-compat-semi.c'))