target-mips: add Unified Hosting Interface (UHI) support

Add UHI semihosting support for MIPS. QEMU run with "-semihosting" option
will alter the behaviour of SDBBP 1 instruction -- UHI operation will be
called instead of generating a debug exception.

Also tweak Malta's pseudo-bootloader. On CPU reset the $4 register is set
to -1 if semihosting arguments are passed to indicate that the UHI
operations should be used to obtain input arguments.

Signed-off-by: Leon Alrae <leon.alrae@imgtec.com>
Reviewed-by: Aurelien Jarno <aurelien@aurel32.net>

hw/mips/mips_malta.c

@@ -53,6 +53,7 @@
 #include "qemu/error-report.h"
 #include "hw/empty_slot.h"
 #include "sysemu/kvm.h"
+#include "exec/semihost.h"
 
 //#define DEBUG_BOARD_INIT
 
@@ -634,7 +635,13 @@ static void write_bootloader (CPUMIPSState *env, uint8_t *base,
 
     /* Second part of the bootloader */
     p = (uint32_t *) (base + 0x580);
-    stl_p(p++, 0x24040002);                                      /* addiu a0, zero, 2 */
+
+    if (semihosting_get_argc()) {
+        /* Preserve a0 content as arguments have been passed */
+        stl_p(p++, 0x00000000);                         /* nop */
+    } else {
+        stl_p(p++, 0x24040002);                         /* addiu a0, zero, 2 */
+    }
     stl_p(p++, 0x3c1d0000 | (((ENVP_ADDR - 64) >> 16) & 0xffff)); /* lui sp, high(ENVP_ADDR) */
     stl_p(p++, 0x37bd0000 | ((ENVP_ADDR - 64) & 0xffff));        /* ori sp, sp, low(ENVP_ADDR) */
     stl_p(p++, 0x3c050000 | ((ENVP_ADDR >> 16) & 0xffff));       /* lui a1, high(ENVP_ADDR) */

qemu-options.hx

@@ -3345,20 +3345,22 @@ Set OpenBIOS nvram @var{variable} to given @var{value} (PPC, SPARC only).
 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_ARM | QEMU_ARCH_M68K | QEMU_ARCH_XTENSA | QEMU_ARCH_LM32 |
+    QEMU_ARCH_MIPS)
 STEXI
 @item -semihosting
 @findex -semihosting
-Enable semihosting mode (ARM, M68K, Xtensa only).
+Enable semihosting mode (ARM, M68K, Xtensa, MIPS 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_ARM | QEMU_ARCH_M68K | QEMU_ARCH_XTENSA | QEMU_ARCH_LM32 |
+QEMU_ARCH_MIPS)
 STEXI
 @item -semihosting-config [enable=on|off][,target=native|gdb|auto][,arg=str[,...]]
 @findex -semihosting-config
-Enable and configure semihosting (ARM, M68K, Xtensa only).
+Enable and configure semihosting (ARM, M68K, Xtensa, MIPS only).
 @table @option
 @item target=@code{native|gdb|auto}
 Defines where the semihosting calls will be addressed, to QEMU (@code{native})

target-mips/Makefile.objs

@@ -1,4 +1,4 @@
 obj-y += translate.o dsp_helper.o op_helper.o lmi_helper.o helper.o cpu.o
-obj-y += gdbstub.o msa_helper.o
+obj-y += gdbstub.o msa_helper.o mips-semi.o
 obj-$(CONFIG_SOFTMMU) += machine.o
 obj-$(CONFIG_KVM) += kvm.o

target-mips/helper.h

@@ -1,6 +1,8 @@
 DEF_HELPER_3(raise_exception_err, noreturn, env, i32, int)
 DEF_HELPER_2(raise_exception, noreturn, env, i32)
 
+DEF_HELPER_1(do_semihosting, void, env)
+
 #ifdef TARGET_MIPS64
 DEF_HELPER_4(sdl, void, env, tl, tl, int)
 DEF_HELPER_4(sdr, void, env, tl, tl, int)

target-mips/mips-semi.c

@@ -0,0 +1,336 @@
+/*
+ * Unified Hosting Interface syscalls.
+ *
+ * Copyright (c) 2015 Imagination Technologies
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <sys/stat.h>
+#include "cpu.h"
+#include "exec/helper-proto.h"
+#include "exec/softmmu-semi.h"
+#include "exec/semihost.h"
+
+typedef enum UHIOp {
+    UHI_exit = 1,
+    UHI_open = 2,
+    UHI_close = 3,
+    UHI_read = 4,
+    UHI_write = 5,
+    UHI_lseek = 6,
+    UHI_unlink = 7,
+    UHI_fstat = 8,
+    UHI_argc = 9,
+    UHI_argnlen = 10,
+    UHI_argn = 11,
+    UHI_plog = 13,
+    UHI_assert = 14,
+    UHI_pread = 19,
+    UHI_pwrite = 20,
+    UHI_link = 22
+} UHIOp;
+
+typedef struct UHIStat {
+    int16_t uhi_st_dev;
+    uint16_t uhi_st_ino;
+    uint32_t uhi_st_mode;
+    uint16_t uhi_st_nlink;
+    uint16_t uhi_st_uid;
+    uint16_t uhi_st_gid;
+    int16_t uhi_st_rdev;
+    uint64_t uhi_st_size;
+    uint64_t uhi_st_atime;
+    uint64_t uhi_st_spare1;
+    uint64_t uhi_st_mtime;
+    uint64_t uhi_st_spare2;
+    uint64_t uhi_st_ctime;
+    uint64_t uhi_st_spare3;
+    uint64_t uhi_st_blksize;
+    uint64_t uhi_st_blocks;
+    uint64_t uhi_st_spare4[2];
+} UHIStat;
+
+enum UHIOpenFlags {
+    UHIOpen_RDONLY = 0x0,
+    UHIOpen_WRONLY = 0x1,
+    UHIOpen_RDWR   = 0x2,
+    UHIOpen_APPEND = 0x8,
+    UHIOpen_CREAT  = 0x200,
+    UHIOpen_TRUNC  = 0x400,
+    UHIOpen_EXCL   = 0x800
+};
+
+static int copy_stat_to_target(CPUMIPSState *env, const struct stat *src,
+                               target_ulong vaddr)
+{
+    hwaddr len = sizeof(struct UHIStat);
+    UHIStat *dst = lock_user(VERIFY_WRITE, vaddr, len, 0);
+    if (!dst) {
+        errno = EFAULT;
+        return -1;
+    }
+
+    dst->uhi_st_dev = tswap16(src->st_dev);
+    dst->uhi_st_ino = tswap16(src->st_ino);
+    dst->uhi_st_mode = tswap32(src->st_mode);
+    dst->uhi_st_nlink = tswap16(src->st_nlink);
+    dst->uhi_st_uid = tswap16(src->st_uid);
+    dst->uhi_st_gid = tswap16(src->st_gid);
+    dst->uhi_st_rdev = tswap16(src->st_rdev);
+    dst->uhi_st_size = tswap64(src->st_size);
+    dst->uhi_st_atime = tswap64(src->st_atime);
+    dst->uhi_st_mtime = tswap64(src->st_mtime);
+    dst->uhi_st_ctime = tswap64(src->st_ctime);
+#ifdef _WIN32
+    dst->uhi_st_blksize = 0;
+    dst->uhi_st_blocks = 0;
+#else
+    dst->uhi_st_blksize = tswap64(src->st_blksize);
+    dst->uhi_st_blocks = tswap64(src->st_blocks);
+#endif
+    unlock_user(dst, vaddr, len);
+    return 0;
+}
+
+static int get_open_flags(target_ulong target_flags)
+{
+    int open_flags = 0;
+
+    if (target_flags & UHIOpen_RDWR) {
+        open_flags |= O_RDWR;
+    } else if (target_flags & UHIOpen_WRONLY) {
+        open_flags |= O_WRONLY;
+    } else {
+        open_flags |= O_RDONLY;
+    }
+
+    open_flags |= (target_flags & UHIOpen_APPEND) ? O_APPEND : 0;
+    open_flags |= (target_flags & UHIOpen_CREAT)  ? O_CREAT  : 0;
+    open_flags |= (target_flags & UHIOpen_TRUNC)  ? O_TRUNC  : 0;
+    open_flags |= (target_flags & UHIOpen_EXCL)   ? O_EXCL   : 0;
+
+    return open_flags;
+}
+
+static int write_to_file(CPUMIPSState *env, target_ulong fd, target_ulong vaddr,
+                         target_ulong len, target_ulong offset)
+{
+    int num_of_bytes;
+    void *dst = lock_user(VERIFY_READ, vaddr, len, 1);
+    if (!dst) {
+        errno = EFAULT;
+        return -1;
+    }
+
+    if (offset) {
+#ifdef _WIN32
+        num_of_bytes = 0;
+#else
+        num_of_bytes = pwrite(fd, dst, len, offset);
+#endif
+    } else {
+        num_of_bytes = write(fd, dst, len);
+    }
+
+    unlock_user(dst, vaddr, 0);
+    return num_of_bytes;
+}
+
+static int read_from_file(CPUMIPSState *env, target_ulong fd,
+                          target_ulong vaddr, target_ulong len,
+                          target_ulong offset)
+{
+    int num_of_bytes;
+    void *dst = lock_user(VERIFY_WRITE, vaddr, len, 0);
+    if (!dst) {
+        errno = EFAULT;
+        return -1;
+    }
+
+    if (offset) {
+#ifdef _WIN32
+        num_of_bytes = 0;
+#else
+        num_of_bytes = pread(fd, dst, len, offset);
+#endif
+    } else {
+        num_of_bytes = read(fd, dst, len);
+    }
+
+    unlock_user(dst, vaddr, len);
+    return num_of_bytes;
+}
+
+static int copy_argn_to_target(CPUMIPSState *env, int arg_num,
+                               target_ulong vaddr)
+{
+    int strsize = strlen(semihosting_get_arg(arg_num)) + 1;
+    char *dst = lock_user(VERIFY_WRITE, vaddr, strsize, 0);
+    if (!dst) {
+        return -1;
+    }
+
+    strcpy(dst, semihosting_get_arg(arg_num));
+
+    unlock_user(dst, vaddr, strsize);
+    return 0;
+}
+
+#define GET_TARGET_STRING(p, addr)              \
+    do {                                        \
+        p = lock_user_string(addr);             \
+        if (!p) {                               \
+            gpr[2] = -1;                        \
+            gpr[3] = EFAULT;                    \
+            goto uhi_done;                      \
+        }                                       \
+    } while (0)
+
+#define FREE_TARGET_STRING(p, gpr)              \
+    do {                                        \
+        unlock_user(p, gpr, 0);                 \
+    } while (0)
+
+void helper_do_semihosting(CPUMIPSState *env)
+{
+    target_ulong *gpr = env->active_tc.gpr;
+    const UHIOp op = gpr[25];
+    char *p, *p2;
+
+    switch (op) {
+    case UHI_exit:
+        qemu_log("UHI(%d): exit(%d)\n", op, (int)gpr[4]);
+        exit(gpr[4]);
+    case UHI_open:
+        GET_TARGET_STRING(p, gpr[4]);
+        if (!strcmp("/dev/stdin", p)) {
+            gpr[2] = 0;
+        } else if (!strcmp("/dev/stdout", p)) {
+            gpr[2] = 1;
+        } else if (!strcmp("/dev/stderr", p)) {
+            gpr[2] = 2;
+        } else {
+            gpr[2] = open(p, get_open_flags(gpr[5]), gpr[6]);
+            gpr[3] = errno;
+        }
+        FREE_TARGET_STRING(p, gpr[4]);
+        break;
+    case UHI_close:
+        if (gpr[4] < 3) {
+            /* ignore closing stdin/stdout/stderr */
+            gpr[2] = 0;
+            goto uhi_done;
+        }
+        gpr[2] = close(gpr[4]);
+        gpr[3] = errno;
+        break;
+    case UHI_read:
+        gpr[2] = read_from_file(env, gpr[4], gpr[5], gpr[6], 0);
+        gpr[3] = errno;
+        break;
+    case UHI_write:
+        gpr[2] = write_to_file(env, gpr[4], gpr[5], gpr[6], 0);
+        gpr[3] = errno;
+        break;
+    case UHI_lseek:
+        gpr[2] = lseek(gpr[4], gpr[5], gpr[6]);
+        gpr[3] = errno;
+        break;
+    case UHI_unlink:
+        GET_TARGET_STRING(p, gpr[4]);
+        gpr[2] = remove(p);
+        gpr[3] = errno;
+        FREE_TARGET_STRING(p, gpr[4]);
+        break;
+    case UHI_fstat:
+        {
+            struct stat sbuf;
+            memset(&sbuf, 0, sizeof(sbuf));
+            gpr[2] = fstat(gpr[4], &sbuf);
+            gpr[3] = errno;
+            if (gpr[2]) {
+                goto uhi_done;
+            }
+            gpr[2] = copy_stat_to_target(env, &sbuf, gpr[5]);
+            gpr[3] = errno;
+        }
+        break;
+    case UHI_argc:
+        gpr[2] = semihosting_get_argc();
+        break;
+    case UHI_argnlen:
+        if (gpr[4] >= semihosting_get_argc()) {
+            gpr[2] = -1;
+            goto uhi_done;
+        }
+        gpr[2] = strlen(semihosting_get_arg(gpr[4]));
+        break;
+    case UHI_argn:
+        if (gpr[4] >= semihosting_get_argc()) {
+            gpr[2] = -1;
+            goto uhi_done;
+        }
+        gpr[2] = copy_argn_to_target(env, gpr[4], gpr[5]);
+        break;
+    case UHI_plog:
+        GET_TARGET_STRING(p, gpr[4]);
+        p2 = strstr(p, "%d");
+        if (p2) {
+            int char_num = p2 - p;
+            char *buf = g_malloc(char_num + 1);
+            strncpy(buf, p, char_num);
+            buf[char_num] = '\0';
+            gpr[2] = printf("%s%d%s", buf, (int)gpr[5], p2 + 2);
+            g_free(buf);
+        } else {
+            gpr[2] = printf("%s", p);
+        }
+        FREE_TARGET_STRING(p, gpr[4]);
+        break;
+    case UHI_assert:
+        GET_TARGET_STRING(p, gpr[4]);
+        GET_TARGET_STRING(p2, gpr[5]);
+        printf("assertion '");
+        printf("\"%s\"", p);
+        printf("': file \"%s\", line %d\n", p2, (int)gpr[6]);
+        FREE_TARGET_STRING(p2, gpr[5]);
+        FREE_TARGET_STRING(p, gpr[4]);
+        abort();
+        break;
+    case UHI_pread:
+        gpr[2] = read_from_file(env, gpr[4], gpr[5], gpr[6], gpr[7]);
+        gpr[3] = errno;
+        break;
+    case UHI_pwrite:
+        gpr[2] = write_to_file(env, gpr[4], gpr[5], gpr[6], gpr[7]);
+        gpr[3] = errno;
+        break;
+#ifndef _WIN32
+    case UHI_link:
+        GET_TARGET_STRING(p, gpr[4]);
+        GET_TARGET_STRING(p2, gpr[5]);
+        gpr[2] = link(p, p2);
+        gpr[3] = errno;
+        FREE_TARGET_STRING(p2, gpr[5]);
+        FREE_TARGET_STRING(p, gpr[4]);
+        break;
+#endif
+    default:
+        fprintf(stderr, "Unknown UHI operation %d\n", op);
+        abort();
+    }
+uhi_done:
+    return;
+}

target-mips/translate.c

@@ -29,6 +29,7 @@
 #include "exec/helper-proto.h"
 #include "exec/helper-gen.h"
 #include "sysemu/kvm.h"
+#include "exec/semihost.h"
 
 #include "trace-tcg.h"
 
@@ -11549,6 +11550,15 @@ static int decode_extended_mips16_opc (CPUMIPSState *env, DisasContext *ctx)
     return 4;
 }
 
+static inline bool is_uhi(int sdbbp_code)
+{
+#ifdef CONFIG_USER_ONLY
+    return false;
+#else
+    return semihosting_enabled() && sdbbp_code == 1;
+#endif
+}
+
 static int decode_mips16_opc (CPUMIPSState *env, DisasContext *ctx)
 {
     int rx, ry;
@@ -11848,11 +11858,15 @@ static int decode_mips16_opc (CPUMIPSState *env, DisasContext *ctx)
             }
             break;
         case RR_SDBBP:
-            /* XXX: not clear which exception should be raised
-             *      when in debug mode...
-             */
-            check_insn(ctx, ISA_MIPS32);
-            generate_exception(ctx, EXCP_DBp);
+            if (is_uhi(extract32(ctx->opcode, 5, 6))) {
+                gen_helper_do_semihosting(cpu_env);
+            } else {
+                /* XXX: not clear which exception should be raised
+                 *      when in debug mode...
+                 */
+                check_insn(ctx, ISA_MIPS32);
+                generate_exception(ctx, EXCP_DBp);
+            }
             break;
         case RR_SLT:
             gen_slt(ctx, OPC_SLT, 24, rx, ry);
@@ -12699,11 +12713,15 @@ static void gen_pool16c_insn(DisasContext *ctx)
         generate_exception(ctx, EXCP_BREAK);
         break;
     case SDBBP16:
-        /* XXX: not clear which exception should be raised
-         *      when in debug mode...
-         */
-        check_insn(ctx, ISA_MIPS32);
-        generate_exception(ctx, EXCP_DBp);
+        if (is_uhi(extract32(ctx->opcode, 0, 4))) {
+            gen_helper_do_semihosting(cpu_env);
+        } else {
+            /* XXX: not clear which exception should be raised
+             *      when in debug mode...
+             */
+            check_insn(ctx, ISA_MIPS32);
+            generate_exception(ctx, EXCP_DBp);
+        }
         break;
     case JRADDIUSP + 0:
     case JRADDIUSP + 1:
@@ -13067,8 +13085,12 @@ static void gen_pool32axf (CPUMIPSState *env, DisasContext *ctx, int rt, int rs)
             ctx->bstate = BS_STOP;
             break;
         case SDBBP:
-            check_insn(ctx, ISA_MIPS32);
-            generate_exception(ctx, EXCP_DBp);
+            if (is_uhi(extract32(ctx->opcode, 16, 10))) {
+                gen_helper_do_semihosting(cpu_env);
+            } else {
+                check_insn(ctx, ISA_MIPS32);
+                generate_exception(ctx, EXCP_DBp);
+            }
             break;
         default:
             goto pool32axf_invalid;
@@ -16460,10 +16482,14 @@ static void decode_opc_special_r6(CPUMIPSState *env, DisasContext *ctx)
         }
         break;
     case R6_OPC_SDBBP:
-        if (ctx->hflags & MIPS_HFLAG_SBRI) {
-            generate_exception(ctx, EXCP_RI);
+        if (is_uhi(extract32(ctx->opcode, 6, 20))) {
+            gen_helper_do_semihosting(cpu_env);
         } else {
-            generate_exception(ctx, EXCP_DBp);
+            if (ctx->hflags & MIPS_HFLAG_SBRI) {
+                generate_exception(ctx, EXCP_RI);
+            } else {
+                generate_exception(ctx, EXCP_DBp);
+            }
         }
         break;
 #if defined(TARGET_MIPS64)
@@ -16833,11 +16859,15 @@ static void decode_opc_special2_legacy(CPUMIPSState *env, DisasContext *ctx)
         gen_cl(ctx, op1, rd, rs);
         break;
     case OPC_SDBBP:
-        /* XXX: not clear which exception should be raised
-         *      when in debug mode...
-         */
-        check_insn(ctx, ISA_MIPS32);
-        generate_exception(ctx, EXCP_DBp);
+        if (is_uhi(extract32(ctx->opcode, 6, 20))) {
+            gen_helper_do_semihosting(cpu_env);
+        } else {
+            /* XXX: not clear which exception should be raised
+             *      when in debug mode...
+             */
+            check_insn(ctx, ISA_MIPS32);
+            generate_exception(ctx, EXCP_DBp);
+        }
         break;
 #if defined(TARGET_MIPS64)
     case OPC_DCLO:
@@ -19910,6 +19940,11 @@ void cpu_state_reset(CPUMIPSState *env)
     restore_flush_mode(env);
     restore_pamask(env);
     cs->exception_index = EXCP_NONE;
+
+    if (semihosting_get_argc()) {
+        /* UHI interface can be used to obtain argc and argv */
+        env->active_tc.gpr[4] = -1;
+    }
 }
 
 void restore_state_to_opc(CPUMIPSState *env, TranslationBlock *tb, int pc_pos)