diff mbox series

[v3,2/2] Add Nios II semihosting support.

Message ID 845fc301f4a7725c239708c58876e3ae4d858fd9.1526671191.git.julian@codesourcery.com
State New
Headers show
Series Nios II generic board config and semihosting support | expand

Commit Message

Julian Brown May 18, 2018, 7:23 p.m. UTC
This patch (by Sandra Loosemore, mildly rebased) adds support for
semihosting for Nios II bare-metal emulation.

Signed-off-by: Julian Brown <julian@codesourcery.com>
Signed-off-by: Sandra Loosemore <sandra@codesourcery.com>
---
 qemu-options.hx            |   8 +-
 target/nios2/Makefile.objs |   2 +-
 target/nios2/cpu.h         |   4 +-
 target/nios2/helper.c      |  11 ++
 target/nios2/nios2-semi.c  | 429 +++++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 448 insertions(+), 6 deletions(-)
 create mode 100644 target/nios2/nios2-semi.c

Comments

Marek Vasut May 18, 2018, 7:52 p.m. UTC | #1
On 05/18/2018 09:23 PM, Julian Brown wrote:
> This patch (by Sandra Loosemore, mildly rebased) adds support for
> semihosting for Nios II bare-metal emulation.
> 
> Signed-off-by: Julian Brown <julian@codesourcery.com>
> Signed-off-by: Sandra Loosemore <sandra@codesourcery.com>

Is there some documentation for this stuff ? It looks interesting, but
how can I try it here ?

[...]
Julian Brown May 18, 2018, 8:19 p.m. UTC | #2
On Fri, 18 May 2018 21:52:04 +0200
Marek Vasut <marex@denx.de> wrote:

> On 05/18/2018 09:23 PM, Julian Brown wrote:
> > This patch (by Sandra Loosemore, mildly rebased) adds support for
> > semihosting for Nios II bare-metal emulation.
> > 
> > Signed-off-by: Julian Brown <julian@codesourcery.com>
> > Signed-off-by: Sandra Loosemore <sandra@codesourcery.com>  
> 
> Is there some documentation for this stuff ? It looks interesting, but
> how can I try it here ?

There's no documentation AFAIK apart from that the entry points are
the same as m68k, semihosting is invoked with "break 1", and r4/r5 are
used for passing arguments. I'm not actually sure how you can try this
stuff without our startup code or other infrastructure (that I'm pretty
sure we can't divulge). Sandra, any ideas?

Thanks,

Julian
Marek Vasut May 18, 2018, 8:28 p.m. UTC | #3
On 05/18/2018 10:19 PM, Julian Brown wrote:
> On Fri, 18 May 2018 21:52:04 +0200
> Marek Vasut <marex@denx.de> wrote:
> 
>> On 05/18/2018 09:23 PM, Julian Brown wrote:
>>> This patch (by Sandra Loosemore, mildly rebased) adds support for
>>> semihosting for Nios II bare-metal emulation.
>>>
>>> Signed-off-by: Julian Brown <julian@codesourcery.com>
>>> Signed-off-by: Sandra Loosemore <sandra@codesourcery.com>  
>>
>> Is there some documentation for this stuff ? It looks interesting, but
>> how can I try it here ?
> 
> There's no documentation AFAIK apart from that the entry points are
> the same as m68k, semihosting is invoked with "break 1", and r4/r5 are
> used for passing arguments.

So, how is anyone supposed to test this if it's shrouded in mystery ?

> I'm not actually sure how you can try this
> stuff without our startup code or other infrastructure (that I'm pretty
> sure we can't divulge). Sandra, any ideas?

So what use is this code in mainline QEMU then ?
Sandra Loosemore May 18, 2018, 9:35 p.m. UTC | #4
On 05/18/2018 02:19 PM, Julian Brown wrote:
> On Fri, 18 May 2018 21:52:04 +0200
> Marek Vasut <marex@denx.de> wrote:
> 
>> On 05/18/2018 09:23 PM, Julian Brown wrote:
>>> This patch (by Sandra Loosemore, mildly rebased) adds support for
>>> semihosting for Nios II bare-metal emulation.
>>>
>>> Signed-off-by: Julian Brown <julian@codesourcery.com>
>>> Signed-off-by: Sandra Loosemore <sandra@codesourcery.com>
>>
>> Is there some documentation for this stuff ? It looks interesting, but
>> how can I try it here ?
> 
> There's no documentation AFAIK apart from that the entry points are
> the same as m68k, semihosting is invoked with "break 1", and r4/r5 are
> used for passing arguments. I'm not actually sure how you can try this
> stuff without our startup code or other infrastructure (that I'm pretty
> sure we can't divulge). Sandra, any ideas?

I don't see any reason why we couldn't contribute libgloss support, 
except that I don't have time to write such a BSP right now.  :-(  I 
recently did this for C-SKY, though, and the semihosting parts were just 
a straightforward copy from the m68k port.

FWIW, CodeSourcery's Nios II ELF toolchains have been using this 
semihosting protocol with a different BSP library all along, and Altera 
also supports it in the proprietary simulators they've provided to us 
for testing.

-Sandra
Sandra Loosemore Aug. 2, 2018, 9:56 p.m. UTC | #5
On 05/18/2018 03:35 PM, Sandra Loosemore wrote:
> On 05/18/2018 02:19 PM, Julian Brown wrote:
>> On Fri, 18 May 2018 21:52:04 +0200
>> Marek Vasut <marex@denx.de> wrote:
>>
>>> On 05/18/2018 09:23 PM, Julian Brown wrote:
>>>> This patch (by Sandra Loosemore, mildly rebased) adds support for
>>>> semihosting for Nios II bare-metal emulation.
>>>>
>>>> Signed-off-by: Julian Brown <julian@codesourcery.com>
>>>> Signed-off-by: Sandra Loosemore <sandra@codesourcery.com>
>>>
>>> Is there some documentation for this stuff ? It looks interesting, but
>>> how can I try it here ?
>>
>> There's no documentation AFAIK apart from that the entry points are
>> the same as m68k, semihosting is invoked with "break 1", and r4/r5 are
>> used for passing arguments. I'm not actually sure how you can try this
>> stuff without our startup code or other infrastructure (that I'm pretty
>> sure we can't divulge). Sandra, any ideas?
> 
> I don't see any reason why we couldn't contribute libgloss support, 
> except that I don't have time to write such a BSP right now.  :-(  I 
> recently did this for C-SKY, though, and the semihosting parts were just 
> a straightforward copy from the m68k port.

I've posted a patch with libgloss semihosting support for nios2 here:

https://sourceware.org/ml/newlib/2018/msg00610.html

I hope this is enough to unblock consideration of the corresponding QEMU 
patch set now.  Here's a link to the original patch posting:

http://lists.nongnu.org/archive/html/qemu-devel/2018-05/msg04571.html

-Sandra
Julian Brown Aug. 13, 2018, 1:03 a.m. UTC | #6
On Thu, 2 Aug 2018 15:56:47 -0600
Sandra Loosemore <sandra@codesourcery.com> wrote:

> On 05/18/2018 03:35 PM, Sandra Loosemore wrote:
> > On 05/18/2018 02:19 PM, Julian Brown wrote:  
> >> On Fri, 18 May 2018 21:52:04 +0200
> >> Marek Vasut <marex@denx.de> wrote:
> >>  
> >>> On 05/18/2018 09:23 PM, Julian Brown wrote:  
> >>>> This patch (by Sandra Loosemore, mildly rebased) adds support for
> >>>> semihosting for Nios II bare-metal emulation.
> >>>>
> >>>> Signed-off-by: Julian Brown <julian@codesourcery.com>
> >>>> Signed-off-by: Sandra Loosemore <sandra@codesourcery.com>  
> >>>
> >>> Is there some documentation for this stuff ? It looks
> >>> interesting, but how can I try it here ?  
> >>
> >> There's no documentation AFAIK apart from that the entry points are
> >> the same as m68k, semihosting is invoked with "break 1", and r4/r5
> >> are used for passing arguments. I'm not actually sure how you can
> >> try this stuff without our startup code or other infrastructure
> >> (that I'm pretty sure we can't divulge). Sandra, any ideas?  
> > 
> > I don't see any reason why we couldn't contribute libgloss support, 
> > except that I don't have time to write such a BSP right now.  :-(
> > I recently did this for C-SKY, though, and the semihosting parts
> > were just a straightforward copy from the m68k port.  
> 
> I've posted a patch with libgloss semihosting support for nios2 here:
> 
> https://sourceware.org/ml/newlib/2018/msg00610.html
> 
> I hope this is enough to unblock consideration of the corresponding
> QEMU patch set now.  Here's a link to the original patch posting:
> 
> http://lists.nongnu.org/archive/html/qemu-devel/2018-05/msg04571.html

For completeness I've re-tested with a rebased QEMU and posted
again (with a couple of checkpatch.pl nits fixed, but otherwise
identical):

http://lists.nongnu.org/archive/html/qemu-devel/2018-08/msg01987.html

Thank you,

Julian
diff mbox series

Patch

diff --git a/qemu-options.hx b/qemu-options.hx
index abbfa6a..626a99e 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -3780,21 +3780,21 @@  ETEXI
 DEF("semihosting", 0, QEMU_OPTION_semihosting,
     "-semihosting    semihosting mode\n",
     QEMU_ARCH_ARM | QEMU_ARCH_M68K | QEMU_ARCH_XTENSA | QEMU_ARCH_LM32 |
-    QEMU_ARCH_MIPS)
+    QEMU_ARCH_MIPS | QEMU_ARCH_NIOS2)
 STEXI
 @item -semihosting
 @findex -semihosting
-Enable semihosting mode (ARM, M68K, Xtensa, MIPS only).
+Enable semihosting mode (ARM, M68K, Xtensa, MIPS, Nios II only).
 ETEXI
 DEF("semihosting-config", HAS_ARG, QEMU_OPTION_semihosting_config,
     "-semihosting-config [enable=on|off][,target=native|gdb|auto][,arg=str[,...]]\n" \
     "                semihosting configuration\n",
 QEMU_ARCH_ARM | QEMU_ARCH_M68K | QEMU_ARCH_XTENSA | QEMU_ARCH_LM32 |
-QEMU_ARCH_MIPS)
+QEMU_ARCH_MIPS | QEMU_ARCH_NIOS2)
 STEXI
 @item -semihosting-config [enable=on|off][,target=native|gdb|auto][,arg=str[,...]]
 @findex -semihosting-config
-Enable and configure semihosting (ARM, M68K, Xtensa, MIPS only).
+Enable and configure semihosting (ARM, M68K, Xtensa, MIPS, Nios II only).
 @table @option
 @item target=@code{native|gdb|auto}
 Defines where the semihosting calls will be addressed, to QEMU (@code{native})
diff --git a/target/nios2/Makefile.objs b/target/nios2/Makefile.objs
index 2a11c5c..010de0e 100644
--- a/target/nios2/Makefile.objs
+++ b/target/nios2/Makefile.objs
@@ -1,4 +1,4 @@ 
-obj-y += translate.o op_helper.o helper.o cpu.o mmu.o
+obj-y += translate.o op_helper.o helper.o cpu.o mmu.o nios2-semi.o
 obj-$(CONFIG_SOFTMMU) += monitor.o
 
 $(obj)/op_helper.o: QEMU_CFLAGS += $(HELPER_CFLAGS)
diff --git a/target/nios2/cpu.h b/target/nios2/cpu.h
index 145796e..a7efb8a 100644
--- a/target/nios2/cpu.h
+++ b/target/nios2/cpu.h
@@ -141,7 +141,7 @@  typedef struct Nios2CPUClass {
 #define R_PC         64
 
 /* Exceptions */
-#define EXCP_BREAK    -1
+#define EXCP_BREAK    0x1000
 #define EXCP_RESET    0
 #define EXCP_PRESET   1
 #define EXCP_IRQ      2
@@ -223,6 +223,8 @@  void nios2_cpu_do_unaligned_access(CPUState *cpu, vaddr addr,
 qemu_irq *nios2_cpu_pic_init(Nios2CPU *cpu);
 void nios2_check_interrupts(CPUNios2State *env);
 
+void do_nios2_semihosting(CPUNios2State *env);
+
 #define TARGET_PHYS_ADDR_SPACE_BITS 32
 #ifdef CONFIG_USER_ONLY
 # define TARGET_VIRT_ADDR_SPACE_BITS 31
diff --git a/target/nios2/helper.c b/target/nios2/helper.c
index a8b8ec6..ca3b087 100644
--- a/target/nios2/helper.c
+++ b/target/nios2/helper.c
@@ -25,6 +25,7 @@ 
 #include "exec/exec-all.h"
 #include "exec/log.h"
 #include "exec/helper-proto.h"
+#include "exec/semihost.h"
 
 #if defined(CONFIG_USER_ONLY)
 
@@ -169,6 +170,16 @@  void nios2_cpu_do_interrupt(CPUState *cs)
         break;
 
     case EXCP_BREAK:
+        qemu_log_mask(CPU_LOG_INT, "BREAK exception at pc=%x\n",
+                      env->regs[R_PC]);
+
+        if (semihosting_enabled()) {
+            qemu_log_mask(CPU_LOG_INT, "Entering semihosting\n");
+            env->regs[R_PC] += 4;
+            do_nios2_semihosting(env);
+            break;
+        }
+
         if ((env->regs[CR_STATUS] & CR_STATUS_EH) == 0) {
             env->regs[CR_BSTATUS] = env->regs[CR_STATUS];
             env->regs[R_BA] = env->regs[R_PC] + 4;
diff --git a/target/nios2/nios2-semi.c b/target/nios2/nios2-semi.c
new file mode 100644
index 0000000..e0d4f3f
--- /dev/null
+++ b/target/nios2/nios2-semi.c
@@ -0,0 +1,429 @@ 
+/*
+ *  Nios II Semihosting syscall interface.
+ *  This code is derived from m68k-semi.c.
+ *
+ *  Copyright (c) 2017 Mentor Graphics
+ *
+ *  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/>.
+ */
+
+#include "qemu/osdep.h"
+
+#include "cpu.h"
+#if defined(CONFIG_USER_ONLY)
+#include "qemu.h"
+#else
+#include "qemu-common.h"
+#include "exec/gdbstub.h"
+#include "exec/softmmu-semi.h"
+#endif
+#include "qemu/log.h"
+#include "sysemu/sysemu.h"
+
+#define HOSTED_EXIT  0
+#define HOSTED_INIT_SIM 1
+#define HOSTED_OPEN 2
+#define HOSTED_CLOSE 3
+#define HOSTED_READ 4
+#define HOSTED_WRITE 5
+#define HOSTED_LSEEK 6
+#define HOSTED_RENAME 7
+#define HOSTED_UNLINK 8
+#define HOSTED_STAT 9
+#define HOSTED_FSTAT 10
+#define HOSTED_GETTIMEOFDAY 11
+#define HOSTED_ISATTY 12
+#define HOSTED_SYSTEM 13
+
+typedef uint32_t gdb_mode_t;
+typedef uint32_t gdb_time_t;
+
+struct nios2_gdb_stat {
+  uint32_t    gdb_st_dev;     /* device */
+  uint32_t    gdb_st_ino;     /* inode */
+  gdb_mode_t  gdb_st_mode;    /* protection */
+  uint32_t    gdb_st_nlink;   /* number of hard links */
+  uint32_t    gdb_st_uid;     /* user ID of owner */
+  uint32_t    gdb_st_gid;     /* group ID of owner */
+  uint32_t    gdb_st_rdev;    /* device type (if inode device) */
+  uint64_t    gdb_st_size;    /* total size, in bytes */
+  uint64_t    gdb_st_blksize; /* blocksize for filesystem I/O */
+  uint64_t    gdb_st_blocks;  /* number of blocks allocated */
+  gdb_time_t  gdb_st_atime;   /* time of last access */
+  gdb_time_t  gdb_st_mtime;   /* time of last modification */
+  gdb_time_t  gdb_st_ctime;   /* time of last change */
+} QEMU_PACKED;
+
+struct gdb_timeval {
+  gdb_time_t tv_sec;  /* second */
+  uint64_t tv_usec;   /* microsecond */
+} QEMU_PACKED;
+
+#define GDB_O_RDONLY   0x0
+#define GDB_O_WRONLY   0x1
+#define GDB_O_RDWR     0x2
+#define GDB_O_APPEND   0x8
+#define GDB_O_CREAT  0x200
+#define GDB_O_TRUNC  0x400
+#define GDB_O_EXCL   0x800
+
+static int translate_openflags(int flags)
+{
+    int hf;
+
+    if (flags & GDB_O_WRONLY)
+        hf = O_WRONLY;
+    else if (flags & GDB_O_RDWR)
+        hf = O_RDWR;
+    else
+        hf = O_RDONLY;
+
+    if (flags & GDB_O_APPEND) hf |= O_APPEND;
+    if (flags & GDB_O_CREAT) hf |= O_CREAT;
+    if (flags & GDB_O_TRUNC) hf |= O_TRUNC;
+    if (flags & GDB_O_EXCL) hf |= O_EXCL;
+
+    return hf;
+}
+
+static void translate_stat(CPUNios2State *env, target_ulong addr, struct stat *s)
+{
+    struct nios2_gdb_stat *p;
+
+    if (!(p = lock_user(VERIFY_WRITE, addr, sizeof(struct nios2_gdb_stat), 0)))
+        /* FIXME - should this return an error code? */
+        return;
+    p->gdb_st_dev = cpu_to_be32(s->st_dev);
+    p->gdb_st_ino = cpu_to_be32(s->st_ino);
+    p->gdb_st_mode = cpu_to_be32(s->st_mode);
+    p->gdb_st_nlink = cpu_to_be32(s->st_nlink);
+    p->gdb_st_uid = cpu_to_be32(s->st_uid);
+    p->gdb_st_gid = cpu_to_be32(s->st_gid);
+    p->gdb_st_rdev = cpu_to_be32(s->st_rdev);
+    p->gdb_st_size = cpu_to_be64(s->st_size);
+#ifdef _WIN32
+    /* Windows stat is missing some fields.  */
+    p->gdb_st_blksize = 0;
+    p->gdb_st_blocks = 0;
+#else
+    p->gdb_st_blksize = cpu_to_be64(s->st_blksize);
+    p->gdb_st_blocks = cpu_to_be64(s->st_blocks);
+#endif
+    p->gdb_st_atime = cpu_to_be32(s->st_atime);
+    p->gdb_st_mtime = cpu_to_be32(s->st_mtime);
+    p->gdb_st_ctime = cpu_to_be32(s->st_ctime);
+    unlock_user(p, addr, sizeof(struct nios2_gdb_stat));
+}
+
+static void nios2_semi_return_u32(CPUNios2State *env, uint32_t ret, uint32_t err)
+{
+    target_ulong args = env->regs[R_ARG1];
+    if (put_user_u32(ret, args) ||
+        put_user_u32(err, args + 4)) {
+        /* The nios2 semihosting ABI does not provide any way to report this
+         * error to the guest, so the best we can do is log it in qemu.
+         * It is always a guest error not to pass us a valid argument block.
+         */
+        qemu_log_mask(LOG_GUEST_ERROR, "nios2-semihosting: return value "
+                      "discarded because argument block not writable\n");
+    }
+}
+
+static void nios2_semi_return_u64(CPUNios2State *env, uint64_t ret, uint32_t err)
+{
+    target_ulong args = env->regs[R_ARG1];
+    if (put_user_u32(ret >> 32, args) ||
+        put_user_u32(ret, args + 4) ||
+        put_user_u32(err, args + 8)) {
+        /* No way to report this via nios2 semihosting ABI; just log it */
+        qemu_log_mask(LOG_GUEST_ERROR, "nios2-semihosting: return value "
+                      "discarded because argument block not writable\n");
+    }
+}
+
+static int nios2_semi_is_fseek;
+
+static void nios2_semi_cb(CPUState *cs, target_ulong ret, target_ulong err)
+{
+    Nios2CPU *cpu = NIOS2_CPU(cs);
+    CPUNios2State *env = &cpu->env;
+
+    if (nios2_semi_is_fseek) {
+        /* FIXME: We've already lost the high bits of the fseek
+           return value.  */
+        nios2_semi_return_u64(env, ret, err);
+        nios2_semi_is_fseek = 0;
+    } else {
+        nios2_semi_return_u32(env, ret, err);
+    }
+}
+
+/* Read the input value from the argument block; fail the semihosting
+ * call if the memory read fails.
+ */
+#define GET_ARG(n) do {                                 \
+    if (get_user_ual(arg ## n, args + (n) * 4)) {       \
+        result = -1;                                    \
+        errno = EFAULT;                                 \
+        goto failed;                                    \
+    }                                                   \
+} while (0)
+
+void do_nios2_semihosting(CPUNios2State *env)
+{
+    int nr;
+    uint32_t args;
+    target_ulong arg0, arg1, arg2, arg3;
+    void *p;
+    void *q;
+    uint32_t len;
+    uint32_t result;
+
+    nr = env->regs[R_ARG0];
+    args = env->regs[R_ARG1];
+    switch (nr) {
+    case HOSTED_EXIT:
+        gdb_exit(env, env->regs[R_ARG0]);
+        exit(env->regs[R_ARG0]);
+    case HOSTED_OPEN:
+        GET_ARG(0);
+        GET_ARG(1);
+        GET_ARG(2);
+        GET_ARG(3);
+        if (use_gdb_syscalls()) {
+            gdb_do_syscall(nios2_semi_cb, "open,%s,%x,%x", arg0, (int)arg1,
+                           arg2, arg3);
+            return;
+        } else {
+            p = lock_user_string(arg0);
+            if (!p) {
+                /* FIXME - check error code? */
+                result = -1;
+            } else {
+                result = open(p, translate_openflags(arg2), arg3);
+                unlock_user(p, arg0, 0);
+            }
+        }
+        break;
+    case HOSTED_CLOSE:
+        {
+            /* Ignore attempts to close stdin/out/err.  */
+            GET_ARG(0);
+            int fd = arg0;
+            if (fd > 2) {
+                if (use_gdb_syscalls()) {
+                    gdb_do_syscall(nios2_semi_cb, "close,%x", arg0);
+                    return;
+                } else {
+                    result = close(fd);
+                }
+            } else {
+                result = 0;
+            }
+            break;
+        }
+    case HOSTED_READ:
+        GET_ARG(0);
+        GET_ARG(1);
+        GET_ARG(2);
+        len = arg2;
+        if (use_gdb_syscalls()) {
+            gdb_do_syscall(nios2_semi_cb, "read,%x,%x,%x",
+                           arg0, arg1, len);
+            return;
+        } else {
+            p = lock_user(VERIFY_WRITE, arg1, len, 0);
+            if (!p) {
+                /* FIXME - check error code? */
+                result = -1;
+            } else {
+                result = read(arg0, p, len);
+                unlock_user(p, arg1, len);
+            }
+        }
+        break;
+    case HOSTED_WRITE:
+        GET_ARG(0);
+        GET_ARG(1);
+        GET_ARG(2);
+        len = arg2;
+        if (use_gdb_syscalls()) {
+            gdb_do_syscall(nios2_semi_cb, "write,%x,%x,%x",
+                           arg0, arg1, len);
+            return;
+        } else {
+            p = lock_user(VERIFY_READ, arg1, len, 1);
+            if (!p) {
+                /* FIXME - check error code? */
+                result = -1;
+            } else {
+                result = write(arg0, p, len);
+                unlock_user(p, arg0, 0);
+            }
+        }
+        break;
+    case HOSTED_LSEEK:
+        {
+            uint64_t off;
+            GET_ARG(0);
+            GET_ARG(1);
+            GET_ARG(2);
+            GET_ARG(3);
+            off = (uint32_t)arg2 | ((uint64_t)arg1 << 32);
+            if (use_gdb_syscalls()) {
+                nios2_semi_is_fseek = 1;
+                gdb_do_syscall(nios2_semi_cb, "fseek,%x,%lx,%x",
+                               arg0, off, arg3);
+            } else {
+                off = lseek(arg0, off, arg3);
+                nios2_semi_return_u64(env, off, errno);
+            }
+            return;
+        }
+    case HOSTED_RENAME:
+        GET_ARG(0);
+        GET_ARG(1);
+        GET_ARG(2);
+        GET_ARG(3);
+        if (use_gdb_syscalls()) {
+            gdb_do_syscall(nios2_semi_cb, "rename,%s,%s",
+                           arg0, (int)arg1, arg2, (int)arg3);
+            return;
+        } else {
+            p = lock_user_string(arg0);
+            q = lock_user_string(arg2);
+            if (!p || !q) {
+                /* FIXME - check error code? */
+                result = -1;
+            } else {
+                result = rename(p, q);
+            }
+            unlock_user(p, arg0, 0);
+            unlock_user(q, arg2, 0);
+        }
+        break;
+    case HOSTED_UNLINK:
+        GET_ARG(0);
+        GET_ARG(1);
+        if (use_gdb_syscalls()) {
+            gdb_do_syscall(nios2_semi_cb, "unlink,%s",
+                           arg0, (int)arg1);
+            return;
+        } else {
+            p = lock_user_string(arg0);
+            if (!p) {
+                /* FIXME - check error code? */
+                result = -1;
+            } else {
+                result = unlink(p);
+                unlock_user(p, arg0, 0);
+            }
+        }
+        break;
+    case HOSTED_STAT:
+        GET_ARG(0);
+        GET_ARG(1);
+        GET_ARG(2);
+        if (use_gdb_syscalls()) {
+            gdb_do_syscall(nios2_semi_cb, "stat,%s,%x",
+                           arg0, (int)arg1, arg2);
+            return;
+        } else {
+            struct stat s;
+            p = lock_user_string(arg0);
+            if (!p) {
+                /* FIXME - check error code? */
+                result = -1;
+            } else {
+                result = stat(p, &s);
+                unlock_user(p, arg0, 0);
+            }
+            if (result == 0) {
+                translate_stat(env, arg2, &s);
+            }
+        }
+        break;
+    case HOSTED_FSTAT:
+        GET_ARG(0);
+        GET_ARG(1);
+        if (use_gdb_syscalls()) {
+            gdb_do_syscall(nios2_semi_cb, "fstat,%x,%x",
+                           arg0, arg1);
+            return;
+        } else {
+            struct stat s;
+            result = fstat(arg0, &s);
+            if (result == 0) {
+                translate_stat(env, arg1, &s);
+            }
+        }
+        break;
+    case HOSTED_GETTIMEOFDAY:
+        GET_ARG(0);
+        GET_ARG(1);
+        if (use_gdb_syscalls()) {
+            gdb_do_syscall(nios2_semi_cb, "gettimeofday,%x,%x",
+                           arg0, arg1);
+            return;
+        } else {
+            qemu_timeval tv;
+            struct gdb_timeval *p;
+            result = qemu_gettimeofday(&tv);
+            if (result != 0) {
+                if (!(p = lock_user(VERIFY_WRITE,
+                                    arg0, sizeof(struct gdb_timeval), 0))) {
+                    /* FIXME - check error code? */
+                    result = -1;
+                } else {
+                    p->tv_sec = cpu_to_be32(tv.tv_sec);
+                    p->tv_usec = cpu_to_be64(tv.tv_usec);
+                    unlock_user(p, arg0, sizeof(struct gdb_timeval));
+                }
+            }
+        }
+        break;
+    case HOSTED_ISATTY:
+        GET_ARG(0);
+        if (use_gdb_syscalls()) {
+            gdb_do_syscall(nios2_semi_cb, "isatty,%x", arg0);
+            return;
+        } else {
+            result = isatty(arg0);
+        }
+        break;
+    case HOSTED_SYSTEM:
+        GET_ARG(0);
+        GET_ARG(1);
+        if (use_gdb_syscalls()) {
+            gdb_do_syscall(nios2_semi_cb, "system,%s",
+                           arg0, (int)arg1);
+            return;
+        } else {
+            p = lock_user_string(arg0);
+            if (!p) {
+                /* FIXME - check error code? */
+                result = -1;
+            } else {
+                result = system(p);
+                unlock_user(p, arg0, 0);
+            }
+        }
+        break;
+    default:
+        cpu_abort(CPU(nios2_env_get_cpu(env)), "Unsupported semihosting syscall %d\n", nr);
+        result = 0;
+    }
+failed:
+    nios2_semi_return_u32(env, result, errno);
+}