hw/char/riscv_htif.c - third_party/qemu - Git at Google

 /*
  * QEMU RISC-V Host Target Interface (HTIF) Emulation
  *
  * Copyright (c) 2016-2017 Sagar Karandikar, sagark@eecs.berkeley.edu
  * Copyright (c) 2017-2018 SiFive, Inc.
  *
  * This provides HTIF device emulation for QEMU. At the moment this allows
  * for identical copies of bbl/linux to run on both spike and QEMU.
  *
  * This program is free software; you can redistribute it and/or modify it
  * under the terms and conditions of the GNU General Public License,
  * version 2 or later, as published by the Free Software Foundation.
  *
  * This program is distributed in the hope 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 "qapi/error.h"
 #include "qemu/log.h"
 #include "hw/char/riscv_htif.h"
 #include "hw/char/serial.h"
 #include "chardev/char.h"
 #include "chardev/char-fe.h"
 #include "qemu/timer.h"
 #include "qemu/error-report.h"
 #include "exec/address-spaces.h"
 #include "sysemu/dma.h"

 #define RISCV_DEBUG_HTIF 0
 #define HTIF_DEBUG(fmt, ...)                                                   \
     do {                                                                       \
         if (RISCV_DEBUG_HTIF) {                                                \
             qemu_log_mask(LOG_TRACE, "%s: " fmt "\n", __func__, ##__VA_ARGS__);\
         }                                                                      \
     } while (0)

 #define HTIF_DEV_SHIFT          56
 #define HTIF_CMD_SHIFT          48

 #define HTIF_DEV_SYSTEM         0
 #define HTIF_DEV_CONSOLE        1

 #define HTIF_SYSTEM_CMD_SYSCALL 0
 #define HTIF_CONSOLE_CMD_GETC   0
 #define HTIF_CONSOLE_CMD_PUTC   1

 /* PK system call number */
 #define PK_SYS_WRITE            64

 const char *sig_file;
 uint8_t line_size = 16;

 static uint64_t fromhost_addr, tohost_addr, begin_sig_addr, end_sig_addr;

 void htif_symbol_callback(const char *st_name, int st_info, uint64_t st_value,
                           uint64_t st_size)
 {
     if (strcmp("fromhost", st_name) == 0) {
         fromhost_addr = st_value;
         if (st_size != 8) {
             error_report("HTIF fromhost must be 8 bytes");
             exit(1);
         }
     } else if (strcmp("tohost", st_name) == 0) {
         tohost_addr = st_value;
         if (st_size != 8) {
             error_report("HTIF tohost must be 8 bytes");
             exit(1);
         }
     } else if (strcmp("begin_signature", st_name) == 0) {
         begin_sig_addr = st_value;
     } else if (strcmp("end_signature", st_name) == 0) {
         end_sig_addr = st_value;
     }
 }

 /*
  * Called by the char dev to see if HTIF is ready to accept input.
  */
 static int htif_can_recv(void *opaque)
 {
     return 1;
 }

 /*
  * Called by the char dev to supply input to HTIF console.
  * We assume that we will receive one character at a time.
  */
 static void htif_recv(void *opaque, const uint8_t *buf, int size)
 {
     HTIFState *s = opaque;

     if (size != 1) {
         return;
     }

     /*
      * TODO - we need to check whether mfromhost is zero which indicates
      *        the device is ready to receive. The current implementation
      *        will drop characters
      */

     uint64_t val_written = s->pending_read;
     uint64_t resp = 0x100 | *buf;

     s->fromhost = (val_written >> 48 << 48) | (resp << 16 >> 16);
 }

 /*
  * Called by the char dev to supply special events to the HTIF console.
  * Not used for HTIF.
  */
 static void htif_event(void *opaque, QEMUChrEvent event)
 {

 }

 static int htif_be_change(void *opaque)
 {
     HTIFState *s = opaque;

     qemu_chr_fe_set_handlers(&s->chr, htif_can_recv, htif_recv, htif_event,
         htif_be_change, s, NULL, true);

     return 0;
 }

 /*
  * See below the tohost register format.
  *
  * Bits 63:56 indicate the "device".
  * Bits 55:48 indicate the "command".
  *
  * Device 0 is the syscall device, which is used to emulate Unixy syscalls.
  * It only implements command 0, which has two subfunctions:
  * - If bit 0 is clear, then bits 47:0 represent a pointer to a struct
  *   describing the syscall.
  * - If bit 1 is set, then bits 47:1 represent an exit code, with a zero
  *   value indicating success and other values indicating failure.
  *
  * Device 1 is the blocking character device.
  * - Command 0 reads a character
  * - Command 1 writes a character from the 8 LSBs of tohost
  *
  * For RV32, the tohost register is zero-extended, so only device=0 and
  * command=0 (i.e. HTIF syscalls/exit codes) are supported.
  */
 static void htif_handle_tohost_write(HTIFState *s, uint64_t val_written)
 {
     uint8_t device = val_written >> HTIF_DEV_SHIFT;
     uint8_t cmd = val_written >> HTIF_CMD_SHIFT;
     uint64_t payload = val_written & 0xFFFFFFFFFFFFULL;
     int resp = 0;

     HTIF_DEBUG("mtohost write: device: %d cmd: %d what: %02" PRIx64
         " -payload: %016" PRIx64 "\n", device, cmd, payload & 0xFF, payload);

     /*
      * Currently, there is a fixed mapping of devices:
      * 0: riscv-tests Pass/Fail Reporting Only (no syscall proxy)
      * 1: Console
      */
     if (unlikely(device == HTIF_DEV_SYSTEM)) {
         /* frontend syscall handler, shutdown and exit code support */
         if (cmd == HTIF_SYSTEM_CMD_SYSCALL) {
             if (payload & 0x1) {
                 /* exit code */
                 int exit_code = payload >> 1;

                 /*
                  * Dump signature data if sig_file is specified and
                  * begin/end_signature symbols exist.
                  */
                 if (sig_file && begin_sig_addr && end_sig_addr) {
                     uint64_t sig_len = end_sig_addr - begin_sig_addr;
                     char *sig_data = g_malloc(sig_len);
                     dma_memory_read(&address_space_memory, begin_sig_addr,
                                     sig_data, sig_len, MEMTXATTRS_UNSPECIFIED);
                     FILE *signature = fopen(sig_file, "w");
                     if (signature == NULL) {
                         error_report("Unable to open %s with error %s",
                                      sig_file, strerror(errno));
                         exit(1);
                     }

                     for (int i = 0; i < sig_len; i += line_size) {
                         for (int j = line_size; j > 0; j--) {
                             if (i + j <= sig_len) {
                                 fprintf(signature, "%02x",
                                         sig_data[i + j - 1] & 0xff);
                             } else {
                                 fprintf(signature, "%02x", 0);
                             }
                         }
                         fprintf(signature, "\n");
                     }

                     fclose(signature);
                     g_free(sig_data);
                 }

                 exit(exit_code);
             } else {
                 uint64_t syscall[8];
                 cpu_physical_memory_read(payload, syscall, sizeof(syscall));
                 if (syscall[0] == PK_SYS_WRITE &&
                     syscall[1] == HTIF_DEV_CONSOLE &&
                     syscall[3] == HTIF_CONSOLE_CMD_PUTC) {
                     uint8_t ch;
                     cpu_physical_memory_read(syscall[2], &ch, 1);
                     qemu_chr_fe_write(&s->chr, &ch, 1);
                     resp = 0x100 | (uint8_t)payload;
                 } else {
                     qemu_log_mask(LOG_UNIMP,
                                   "pk syscall proxy not supported\n");
                 }
             }
         } else {
             qemu_log("HTIF device %d: unknown command\n", device);
         }
     } else if (likely(device == HTIF_DEV_CONSOLE)) {
         /* HTIF Console */
         if (cmd == HTIF_CONSOLE_CMD_GETC) {
             /* this should be a queue, but not yet implemented as such */
             s->pending_read = val_written;
             s->tohost = 0; /* clear to indicate we read */
             return;
         } else if (cmd == HTIF_CONSOLE_CMD_PUTC) {
             qemu_chr_fe_write(&s->chr, (uint8_t *)&payload, 1);
             resp = 0x100 | (uint8_t)payload;
         } else {
             qemu_log("HTIF device %d: unknown command\n", device);
         }
     } else {
         qemu_log("HTIF unknown device or command\n");
         HTIF_DEBUG("device: %d cmd: %d what: %02" PRIx64
             " payload: %016" PRIx64, device, cmd, payload & 0xFF, payload);
     }
     /*
      * Latest bbl does not set fromhost to 0 if there is a value in tohost.
      * With this code enabled, qemu hangs waiting for fromhost to go to 0.
      * With this code disabled, qemu works with bbl priv v1.9.1 and v1.10.
      * HTIF needs protocol documentation and a more complete state machine.
      *
      *  while (!s->fromhost_inprogress &&
      *      s->fromhost != 0x0) {
      *  }
      */
     s->fromhost = (val_written >> 48 << 48) | (resp << 16 >> 16);
     s->tohost = 0; /* clear to indicate we read */
 }

 #define TOHOST_OFFSET1      (s->tohost_offset)
 #define TOHOST_OFFSET2      (s->tohost_offset + 4)
 #define FROMHOST_OFFSET1    (s->fromhost_offset)
 #define FROMHOST_OFFSET2    (s->fromhost_offset + 4)

 /* CPU wants to read an HTIF register */
 static uint64_t htif_mm_read(void *opaque, hwaddr addr, unsigned size)
 {
     HTIFState *s = opaque;
     if (addr == TOHOST_OFFSET1) {
         return s->tohost & 0xFFFFFFFF;
     } else if (addr == TOHOST_OFFSET2) {
         return (s->tohost >> 32) & 0xFFFFFFFF;
     } else if (addr == FROMHOST_OFFSET1) {
         return s->fromhost & 0xFFFFFFFF;
     } else if (addr == FROMHOST_OFFSET2) {
         return (s->fromhost >> 32) & 0xFFFFFFFF;
     } else {
         qemu_log("Invalid htif read: address %016" PRIx64 "\n",
             (uint64_t)addr);
         return 0;
     }
 }

 /* CPU wrote to an HTIF register */
 static void htif_mm_write(void *opaque, hwaddr addr,
                           uint64_t value, unsigned size)
 {
     HTIFState *s = opaque;
     if (addr == TOHOST_OFFSET1) {
         if (s->tohost == 0x0) {
             s->allow_tohost = 1;
             s->tohost = value & 0xFFFFFFFF;
         } else {
             s->allow_tohost = 0;
         }
     } else if (addr == TOHOST_OFFSET2) {
         if (s->allow_tohost) {
             s->tohost |= value << 32;
             htif_handle_tohost_write(s, s->tohost);
         }
     } else if (addr == FROMHOST_OFFSET1) {
         s->fromhost_inprogress = 1;
         s->fromhost = value & 0xFFFFFFFF;
     } else if (addr == FROMHOST_OFFSET2) {
         s->fromhost |= value << 32;
         s->fromhost_inprogress = 0;
     } else {
         qemu_log("Invalid htif write: address %016" PRIx64 "\n",
             (uint64_t)addr);
     }
 }

 static const MemoryRegionOps htif_mm_ops = {
     .read = htif_mm_read,
     .write = htif_mm_write,
 };

 HTIFState *htif_mm_init(MemoryRegion *address_space, Chardev *chr,
                         uint64_t nonelf_base, bool custom_base)
 {
     uint64_t base, size, tohost_offset, fromhost_offset;

     if (custom_base) {
         fromhost_addr = nonelf_base;
         tohost_addr = nonelf_base + 8;
     } else {
         if (!fromhost_addr || !tohost_addr) {
             error_report("Invalid HTIF fromhost or tohost address");
             exit(1);
         }
     }

     base = MIN(tohost_addr, fromhost_addr);
     size = MAX(tohost_addr + 8, fromhost_addr + 8) - base;
     tohost_offset = tohost_addr - base;
     fromhost_offset = fromhost_addr - base;

     HTIFState *s = g_new0(HTIFState, 1);
     s->tohost_offset = tohost_offset;
     s->fromhost_offset = fromhost_offset;
     s->pending_read = 0;
     s->allow_tohost = 0;
     s->fromhost_inprogress = 0;
     qemu_chr_fe_init(&s->chr, chr, &error_abort);
     qemu_chr_fe_set_handlers(&s->chr, htif_can_recv, htif_recv, htif_event,
         htif_be_change, s, NULL, true);

     memory_region_init_io(&s->mmio, NULL, &htif_mm_ops, s,
                           TYPE_HTIF_UART, size);
     memory_region_add_subregion_overlap(address_space, base,
                                         &s->mmio, 1);

     return s;
 }
	/*
	* QEMU RISC-V Host Target Interface (HTIF) Emulation
	*
	* Copyright (c) 2016-2017 Sagar Karandikar, sagark@eecs.berkeley.edu
	* Copyright (c) 2017-2018 SiFive, Inc.
	*
	* This provides HTIF device emulation for QEMU. At the moment this allows
	* for identical copies of bbl/linux to run on both spike and QEMU.
	*
	* This program is free software; you can redistribute it and/or modify it
	* under the terms and conditions of the GNU General Public License,
	* version 2 or later, as published by the Free Software Foundation.
	*
	* This program is distributed in the hope 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 "qapi/error.h"
	#include "qemu/log.h"
	#include "hw/char/riscv_htif.h"
	#include "hw/char/serial.h"
	#include "chardev/char.h"
	#include "chardev/char-fe.h"
	#include "qemu/timer.h"
	#include "qemu/error-report.h"
	#include "exec/address-spaces.h"
	#include "sysemu/dma.h"

	#define RISCV_DEBUG_HTIF 0
	#define HTIF_DEBUG(fmt, ...) \
	do { \
	if (RISCV_DEBUG_HTIF) { \
	qemu_log_mask(LOG_TRACE, "%s: " fmt "\n", __func__, ##__VA_ARGS__);\
	} \
	} while (0)

	#define HTIF_DEV_SHIFT 56
	#define HTIF_CMD_SHIFT 48

	#define HTIF_DEV_SYSTEM 0
	#define HTIF_DEV_CONSOLE 1

	#define HTIF_SYSTEM_CMD_SYSCALL 0
	#define HTIF_CONSOLE_CMD_GETC 0
	#define HTIF_CONSOLE_CMD_PUTC 1

	/* PK system call number */
	#define PK_SYS_WRITE 64

	const char *sig_file;
	uint8_t line_size = 16;

	static uint64_t fromhost_addr, tohost_addr, begin_sig_addr, end_sig_addr;

	void htif_symbol_callback(const char *st_name, int st_info, uint64_t st_value,
	uint64_t st_size)
	{
	if (strcmp("fromhost", st_name) == 0) {
	fromhost_addr = st_value;
	if (st_size != 8) {
	error_report("HTIF fromhost must be 8 bytes");
	exit(1);
	}
	} else if (strcmp("tohost", st_name) == 0) {
	tohost_addr = st_value;
	if (st_size != 8) {
	error_report("HTIF tohost must be 8 bytes");
	exit(1);
	}
	} else if (strcmp("begin_signature", st_name) == 0) {
	begin_sig_addr = st_value;
	} else if (strcmp("end_signature", st_name) == 0) {
	end_sig_addr = st_value;
	}
	}

	/*
	* Called by the char dev to see if HTIF is ready to accept input.
	*/
	static int htif_can_recv(void *opaque)
	{
	return 1;
	}

	/*
	* Called by the char dev to supply input to HTIF console.
	* We assume that we will receive one character at a time.
	*/
	static void htif_recv(void opaque, const uint8_t buf, int size)
	{
	HTIFState *s = opaque;

	if (size != 1) {
	return;
	}

	/*
	* TODO - we need to check whether mfromhost is zero which indicates
	* the device is ready to receive. The current implementation
	* will drop characters
	*/

	uint64_t val_written = s->pending_read;
	uint64_t resp = 0x100 \| *buf;

	s->fromhost = (val_written >> 48 << 48) \| (resp << 16 >> 16);
	}

	/*
	* Called by the char dev to supply special events to the HTIF console.
	* Not used for HTIF.
	*/
	static void htif_event(void *opaque, QEMUChrEvent event)
	{

	}

	static int htif_be_change(void *opaque)
	{
	HTIFState *s = opaque;

	qemu_chr_fe_set_handlers(&s->chr, htif_can_recv, htif_recv, htif_event,
	htif_be_change, s, NULL, true);

	return 0;
	}

	/*
	* See below the tohost register format.
	*
	* Bits 63:56 indicate the "device".
	* Bits 55:48 indicate the "command".
	*
	* Device 0 is the syscall device, which is used to emulate Unixy syscalls.
	* It only implements command 0, which has two subfunctions:
	* - If bit 0 is clear, then bits 47:0 represent a pointer to a struct
	* describing the syscall.
	* - If bit 1 is set, then bits 47:1 represent an exit code, with a zero
	* value indicating success and other values indicating failure.
	*
	* Device 1 is the blocking character device.
	* - Command 0 reads a character
	* - Command 1 writes a character from the 8 LSBs of tohost
	*
	* For RV32, the tohost register is zero-extended, so only device=0 and
	* command=0 (i.e. HTIF syscalls/exit codes) are supported.
	*/
	static void htif_handle_tohost_write(HTIFState *s, uint64_t val_written)
	{
	uint8_t device = val_written >> HTIF_DEV_SHIFT;
	uint8_t cmd = val_written >> HTIF_CMD_SHIFT;
	uint64_t payload = val_written & 0xFFFFFFFFFFFFULL;
	int resp = 0;

	HTIF_DEBUG("mtohost write: device: %d cmd: %d what: %02" PRIx64
	" -payload: %016" PRIx64 "\n", device, cmd, payload & 0xFF, payload);

	/*
	* Currently, there is a fixed mapping of devices:
	* 0: riscv-tests Pass/Fail Reporting Only (no syscall proxy)
	* 1: Console
	*/
	if (unlikely(device == HTIF_DEV_SYSTEM)) {
	/* frontend syscall handler, shutdown and exit code support */
	if (cmd == HTIF_SYSTEM_CMD_SYSCALL) {
	if (payload & 0x1) {
	/* exit code */
	int exit_code = payload >> 1;

	/*
	* Dump signature data if sig_file is specified and
	* begin/end_signature symbols exist.
	*/
	if (sig_file && begin_sig_addr && end_sig_addr) {
	uint64_t sig_len = end_sig_addr - begin_sig_addr;
	char *sig_data = g_malloc(sig_len);
	dma_memory_read(&address_space_memory, begin_sig_addr,
	sig_data, sig_len, MEMTXATTRS_UNSPECIFIED);
	FILE *signature = fopen(sig_file, "w");
	if (signature == NULL) {
	error_report("Unable to open %s with error %s",
	sig_file, strerror(errno));
	exit(1);
	}

	for (int i = 0; i < sig_len; i += line_size) {
	for (int j = line_size; j > 0; j--) {
	if (i + j <= sig_len) {
	fprintf(signature, "%02x",
	sig_data[i + j - 1] & 0xff);
	} else {
	fprintf(signature, "%02x", 0);
	}
	}
	fprintf(signature, "\n");
	}

	fclose(signature);
	g_free(sig_data);
	}

	exit(exit_code);
	} else {
	uint64_t syscall[8];
	cpu_physical_memory_read(payload, syscall, sizeof(syscall));
	if (syscall[0] == PK_SYS_WRITE &&
	syscall[1] == HTIF_DEV_CONSOLE &&
	syscall[3] == HTIF_CONSOLE_CMD_PUTC) {
	uint8_t ch;
	cpu_physical_memory_read(syscall[2], &ch, 1);
	qemu_chr_fe_write(&s->chr, &ch, 1);
	resp = 0x100 \| (uint8_t)payload;
	} else {
	qemu_log_mask(LOG_UNIMP,
	"pk syscall proxy not supported\n");
	}
	}
	} else {
	qemu_log("HTIF device %d: unknown command\n", device);
	}
	} else if (likely(device == HTIF_DEV_CONSOLE)) {
	/* HTIF Console */
	if (cmd == HTIF_CONSOLE_CMD_GETC) {
	/* this should be a queue, but not yet implemented as such */
	s->pending_read = val_written;
	s->tohost = 0; /* clear to indicate we read */
	return;
	} else if (cmd == HTIF_CONSOLE_CMD_PUTC) {
	qemu_chr_fe_write(&s->chr, (uint8_t *)&payload, 1);
	resp = 0x100 \| (uint8_t)payload;
	} else {
	qemu_log("HTIF device %d: unknown command\n", device);
	}
	} else {
	qemu_log("HTIF unknown device or command\n");
	HTIF_DEBUG("device: %d cmd: %d what: %02" PRIx64
	" payload: %016" PRIx64, device, cmd, payload & 0xFF, payload);
	}
	/*
	* Latest bbl does not set fromhost to 0 if there is a value in tohost.
	* With this code enabled, qemu hangs waiting for fromhost to go to 0.
	* With this code disabled, qemu works with bbl priv v1.9.1 and v1.10.
	* HTIF needs protocol documentation and a more complete state machine.
	*
	* while (!s->fromhost_inprogress &&
	* s->fromhost != 0x0) {
	* }
	*/
	s->fromhost = (val_written >> 48 << 48) \| (resp << 16 >> 16);
	s->tohost = 0; /* clear to indicate we read */
	}

	#define TOHOST_OFFSET1 (s->tohost_offset)
	#define TOHOST_OFFSET2 (s->tohost_offset + 4)
	#define FROMHOST_OFFSET1 (s->fromhost_offset)
	#define FROMHOST_OFFSET2 (s->fromhost_offset + 4)

	/* CPU wants to read an HTIF register */
	static uint64_t htif_mm_read(void *opaque, hwaddr addr, unsigned size)
	{
	HTIFState *s = opaque;
	if (addr == TOHOST_OFFSET1) {
	return s->tohost & 0xFFFFFFFF;
	} else if (addr == TOHOST_OFFSET2) {
	return (s->tohost >> 32) & 0xFFFFFFFF;
	} else if (addr == FROMHOST_OFFSET1) {
	return s->fromhost & 0xFFFFFFFF;
	} else if (addr == FROMHOST_OFFSET2) {
	return (s->fromhost >> 32) & 0xFFFFFFFF;
	} else {
	qemu_log("Invalid htif read: address %016" PRIx64 "\n",
	(uint64_t)addr);
	return 0;
	}
	}

	/* CPU wrote to an HTIF register */
	static void htif_mm_write(void *opaque, hwaddr addr,
	uint64_t value, unsigned size)
	{
	HTIFState *s = opaque;
	if (addr == TOHOST_OFFSET1) {
	if (s->tohost == 0x0) {
	s->allow_tohost = 1;
	s->tohost = value & 0xFFFFFFFF;
	} else {
	s->allow_tohost = 0;
	}
	} else if (addr == TOHOST_OFFSET2) {
	if (s->allow_tohost) {
	s->tohost \|= value << 32;
	htif_handle_tohost_write(s, s->tohost);
	}
	} else if (addr == FROMHOST_OFFSET1) {
	s->fromhost_inprogress = 1;
	s->fromhost = value & 0xFFFFFFFF;
	} else if (addr == FROMHOST_OFFSET2) {
	s->fromhost \|= value << 32;
	s->fromhost_inprogress = 0;
	} else {
	qemu_log("Invalid htif write: address %016" PRIx64 "\n",
	(uint64_t)addr);
	}
	}

	static const MemoryRegionOps htif_mm_ops = {
	.read = htif_mm_read,
	.write = htif_mm_write,
	};

	HTIFState htif_mm_init(MemoryRegion address_space, Chardev *chr,
	uint64_t nonelf_base, bool custom_base)
	{
	uint64_t base, size, tohost_offset, fromhost_offset;

	if (custom_base) {
	fromhost_addr = nonelf_base;
	tohost_addr = nonelf_base + 8;
	} else {
	if (!fromhost_addr \|\| !tohost_addr) {
	error_report("Invalid HTIF fromhost or tohost address");
	exit(1);
	}
	}

	base = MIN(tohost_addr, fromhost_addr);
	size = MAX(tohost_addr + 8, fromhost_addr + 8) - base;
	tohost_offset = tohost_addr - base;
	fromhost_offset = fromhost_addr - base;

	HTIFState *s = g_new0(HTIFState, 1);
	s->tohost_offset = tohost_offset;
	s->fromhost_offset = fromhost_offset;
	s->pending_read = 0;
	s->allow_tohost = 0;
	s->fromhost_inprogress = 0;
	qemu_chr_fe_init(&s->chr, chr, &error_abort);
	qemu_chr_fe_set_handlers(&s->chr, htif_can_recv, htif_recv, htif_event,
	htif_be_change, s, NULL, true);

	memory_region_init_io(&s->mmio, NULL, &htif_mm_ops, s,
	TYPE_HTIF_UART, size);
	memory_region_add_subregion_overlap(address_space, base,
	&s->mmio, 1);

	return s;
	}