diff --git a/hw/acpi.c b/hw/acpi.c
index 8071e7b..b058e20 100644
--- a/hw/acpi.c
+++ b/hw/acpi.c
@@ -32,6 +32,30 @@ struct acpi_table_header
     uint32_t asl_compiler_revision; /* ASL compiler revision number */
 } __attribute__((packed));
 
+#define ACPI_TABLE_OFF(x)       (offsetof(struct acpi_table_header, x))
+#define ACPI_TABLE_SIZE(x)      (sizeof(((struct acpi_table_header*)0)->x))
+
+#define ACPI_TABLE_SIG_OFF              ACPI_TABLE_OFF(signature)
+#define ACPI_TABLE_SIG_SIZE             ACPI_TABLE_SIZE(signature)
+#define ACPI_TABLE_LEN_OFF              ACPI_TABLE_OFF(length)
+#define ACPI_TABLE_LEN_SIZE             ACPI_TABLE_SIZE(length)
+#define ACPI_TABLE_REV_OFF              ACPI_TABLE_OFF(revision)
+#define ACPI_TABLE_REV_SIZE             ACPI_TABLE_SIZE(revision)
+#define ACPI_TABLE_CSUM_OFF             ACPI_TABLE_OFF(checksum)
+#define ACPI_TABLE_CSUM_SIZE            ACPI_TABLE_SIZE(checksum)
+#define ACPI_TABLE_OEM_ID_OFF           ACPI_TABLE_OFF(oem_id)
+#define ACPI_TABLE_OEM_ID_SIZE          ACPI_TABLE_SIZE(oem_id)
+#define ACPI_TABLE_OEM_TABLE_ID_OFF     ACPI_TABLE_OFF(oem_table_id)
+#define ACPI_TABLE_OEM_TABLE_ID_SIZE    ACPI_TABLE_SIZE(oem_table_id)
+#define ACPI_TABLE_OEM_REV_OFF          ACPI_TABLE_OFF(oem_revision)
+#define ACPI_TABLE_OEM_REV_SIZE         ACPI_TABLE_SIZE(oem_revision)
+#define ACPI_TABLE_ASL_COMPILER_ID_OFF  ACPI_TABLE_OFF(asl_compiler_id)
+#define ACPI_TABLE_ASL_COMPILER_ID_SIZE ACPI_TABLE_SIZE(asl_compiler_id)
+#define ACPI_TABLE_ASL_COMPILER_REV_OFF ACPI_TABLE_OFF(asl_compiler_revision)
+#define ACPI_TABLE_ASL_COMPILER_REV_SIZE ACPI_TABLE_SIZE(asl_compiler_revision)
+
+#define ACPI_TABLE_HDR_SIZE sizeof(struct acpi_table_header)
+
 char *acpi_tables;
 size_t acpi_tables_len;
 
@@ -44,156 +68,206 @@ static int acpi_checksum(const uint8_t *data, int len)
     return (-sum) & 0xff;
 }
 
+/* XXX fixme: this function uses obsolete argument parsing interface */
 int acpi_table_add(const char *t)
 {
     static const char *dfl_id = "QEMUQEMU";
-    char buf[1024], *p, *f;
-    struct acpi_table_header acpi_hdr;
+    char buf[1024], *f, *p;
     unsigned long val;
-    uint32_t length;
-    struct acpi_table_header *acpi_hdr_p;
-    size_t off;
+    uint16_t val16;
+    uint32_t val32;
+    size_t len, start;
+    bool has_header;
+    int changed;
 
-    memset(&acpi_hdr, 0, sizeof(acpi_hdr));
-  
-    if (get_param_value(buf, sizeof(buf), "sig", t)) {
-        strncpy(acpi_hdr.signature, buf, 4);
+    if (get_param_value(buf, sizeof(buf), "data", t)) {
+        has_header = false;
+    } else if (get_param_value(buf, sizeof(buf), "file", t)) {
+        has_header = true;
     } else {
-        strncpy(acpi_hdr.signature, dfl_id, 4);
+        has_header = 0;
+        buf[0] = '\0';
+    }
+
+    if (!acpi_tables) {
+        acpi_tables_len = sizeof(uint16_t);
+        acpi_tables = qemu_mallocz(acpi_tables_len);
+    }
+    start = acpi_tables_len;
+
+    len = sizeof(uint16_t) + ACPI_TABLE_HDR_SIZE;
+    acpi_tables = qemu_realloc(acpi_tables, acpi_tables_len + len);
+    acpi_tables_len += sizeof(uint16_t);
+
+    if (!has_header) {
+        memset(acpi_tables + acpi_tables_len, 0, ACPI_TABLE_HDR_SIZE);
+        acpi_tables_len += ACPI_TABLE_HDR_SIZE;
     }
+
+    /* now read in the data files, reallocating buffer as needed */
+    for(f = strtok(buf, ":"); f; f = strtok(NULL, ":")) {
+        int fd = open(f, O_RDONLY);
+        if(fd < 0) {
+            fprintf(stderr, "can't open file %s: %s\n", f, strerror(errno));
+            goto out;
+        }
+
+        for(;;) {
+            char data[8192];
+            ssize_t r = read(fd, data, sizeof(data));
+            if (r == 0) {
+                break;
+            } else if (r > 0) {
+                acpi_tables = qemu_realloc(acpi_tables, acpi_tables_len + r);
+                memcpy(acpi_tables + acpi_tables_len, data, r);
+                acpi_tables_len += r;
+            } else if (errno != EINTR) {
+                fprintf(stderr, "can't read file %s: %s\n",
+                        f, strerror(errno));
+                close(fd);
+                goto out;
+            }
+        }
+
+        close(fd);
+    }
+
+    /* fill in the complete length of the table */
+    len = acpi_tables_len - start - sizeof(uint16_t);
+    f = acpi_tables + start;
+    val16 = cpu_to_le16(len);
+    memcpy(f, &val16, sizeof(uint16_t));
+    f += sizeof(uint16_t);
+
+    /* now fill in the header fields */
+    changed = 0;
+
+    /* 0..3, signature, string (4 bytes) */
+    if (get_param_value(buf, sizeof(buf), "sig", t)) {
+        strncpy(f + ACPI_TABLE_SIG_OFF, buf, ACPI_TABLE_SIG_SIZE);
+        ++changed;
+    } else if (!has_header) {
+        strncpy(f + ACPI_TABLE_SIG_OFF, dfl_id, ACPI_TABLE_SIG_SIZE);
+    }
+
+    /* 4..7, length of the table, in bytes, including header (4 bytes) */
+
+    /* 8, ACPI specification minor version #, 1 byte */
     if (get_param_value(buf, sizeof(buf), "rev", t)) {
         val = strtoul(buf, &p, 10);
-        if (val > 255 || *p != '\0')
+        if (val > 255 || *p != '\0') {
+            fprintf(stderr, "invalid acpi rev.\n");
             goto out;
-    } else {
-        val = 1;
+        }
+        f[ACPI_TABLE_REV_OFF] = (uint8_t)val;
+        ++changed;
+    } else if (!has_header) {
+        f[ACPI_TABLE_REV_OFF] = 1;
     }
-    acpi_hdr.revision = (int8_t)val;
 
+    /* 9, checksum of entire table (1 byte)
+       this will be processed after all the headers are modified */
+
+    /* 10..15 OEM identification (6 bytes) */
     if (get_param_value(buf, sizeof(buf), "oem_id", t)) {
-        strncpy(acpi_hdr.oem_id, buf, 6);
-    } else {
-        strncpy(acpi_hdr.oem_id, dfl_id, 6);
+        strncpy(f + ACPI_TABLE_OEM_ID_OFF, buf, ACPI_TABLE_OEM_ID_SIZE);
+        ++changed;
+    } else if (!has_header) {
+        strncpy(f + ACPI_TABLE_OEM_ID_OFF, dfl_id, ACPI_TABLE_OEM_ID_SIZE);
     }
 
+    /* 16..23 OEM table identifiaction, 8 bytes */
     if (get_param_value(buf, sizeof(buf), "oem_table_id", t)) {
-        strncpy(acpi_hdr.oem_table_id, buf, 8);
-    } else {
-        strncpy(acpi_hdr.oem_table_id, dfl_id, 8);
+        strncpy(f + ACPI_TABLE_OEM_TABLE_ID_OFF, buf,
+                ACPI_TABLE_OEM_TABLE_ID_SIZE);
+        ++changed;
+    } else if (!has_header) {
+        strncpy(f + ACPI_TABLE_OEM_TABLE_ID_OFF, dfl_id,
+                ACPI_TABLE_OEM_TABLE_ID_SIZE);
     }
 
+    /* 24..27 OEM revision number, 4 bytes */
     if (get_param_value(buf, sizeof(buf), "oem_rev", t)) {
         val = strtol(buf, &p, 10);
-        if(*p != '\0')
+        if(*p != '\0') {
+            fprintf(stderr, "invalid acpi oem_rev.\n");
             goto out;
-    } else {
-        val = 1;
+        }
+        val32 = cpu_to_le32(val);
+        memcpy(f + ACPI_TABLE_OEM_REV_OFF, &val32, ACPI_TABLE_OEM_REV_SIZE);
+        ++changed;
+    } else if (!has_header) {
+        val32 = cpu_to_le32(1);
+        memcpy(f + ACPI_TABLE_OEM_REV_OFF, &val32, ACPI_TABLE_OEM_REV_SIZE);
     }
-    acpi_hdr.oem_revision = cpu_to_le32(val);
 
+    /* 28..31 ASL compiler vendor ID (4 bytes) */
     if (get_param_value(buf, sizeof(buf), "asl_compiler_id", t)) {
-        strncpy(acpi_hdr.asl_compiler_id, buf, 4);
-    } else {
-        strncpy(acpi_hdr.asl_compiler_id, dfl_id, 4);
+        strncpy(f + ACPI_TABLE_ASL_COMPILER_ID_OFF, buf,
+                ACPI_TABLE_ASL_COMPILER_ID_SIZE);
+        ++changed;
+    } else if (!has_header) {
+        strncpy(f + ACPI_TABLE_ASL_COMPILER_ID_OFF, dfl_id,
+                ACPI_TABLE_ASL_COMPILER_ID_SIZE);
     }
 
+    /* 32..35 ASL compiler revision number (4 bytes) */
     if (get_param_value(buf, sizeof(buf), "asl_compiler_rev", t)) {
         val = strtol(buf, &p, 10);
-        if(*p != '\0')
-            goto out;
-    } else {
-        val = 1;
-    }
-    acpi_hdr.asl_compiler_revision = cpu_to_le32(val);
-    
-    if (!get_param_value(buf, sizeof(buf), "data", t)) {
-         buf[0] = '\0';
-    }
-
-    length = sizeof(acpi_hdr);
-
-    f = buf;
-    while (buf[0]) {
-        struct stat s;
-        char *n = strchr(f, ':');
-        if (n)
-            *n = '\0';
-        if(stat(f, &s) < 0) {
-            fprintf(stderr, "Can't stat file '%s': %s\n", f, strerror(errno));
+        if(*p != '\0') {
+            fprintf(stderr, "invalid acpi asl_compiler_rev.\n");
             goto out;
         }
-        length += s.st_size;
-        if (!n)
-            break;
-        *n = ':';
-        f = n + 1;
-    }
+        val32 = cpu_to_le32(val);
+        memcpy(f + ACPI_TABLE_ASL_COMPILER_REV_OFF, &val32,
+               ACPI_TABLE_ASL_COMPILER_REV_SIZE);
+        ++changed;
+    } else if (!has_header) {
+        val32 = cpu_to_le32(1);
+        memcpy(f + ACPI_TABLE_ASL_COMPILER_REV_OFF, &val32,
+               ACPI_TABLE_ASL_COMPILER_REV_SIZE);
 
-    if (!acpi_tables) {
-        acpi_tables_len = sizeof(uint16_t);
-        acpi_tables = qemu_mallocz(acpi_tables_len);
     }
-    acpi_tables = qemu_realloc(acpi_tables,
-                               acpi_tables_len + sizeof(uint16_t) + length);
-    p = acpi_tables + acpi_tables_len;
-    acpi_tables_len += sizeof(uint16_t) + length;
-
-    *(uint16_t*)p = cpu_to_le32(length);
-    p += sizeof(uint16_t);
-    memcpy(p, &acpi_hdr, sizeof(acpi_hdr));
-    off = sizeof(acpi_hdr);
-
-    f = buf;
-    while (buf[0]) {
-        struct stat s;
-        int fd;
-        char *n = strchr(f, ':');
-        if (n)
-            *n = '\0';
-        fd = open(f, O_RDONLY);
-
-        if(fd < 0)
-            goto out;
-        if(fstat(fd, &s) < 0) {
-            close(fd);
-            goto out;
-        }
 
-        /* off < length is necessary because file size can be changed
-           under our foot */
-        while(s.st_size && off < length) {
-            int r;
-            r = read(fd, p + off, s.st_size);
-            if (r > 0) {
-                off += r;
-                s.st_size -= r;
-            } else if ((r < 0 && errno != EINTR) || r == 0) {
-                close(fd);
-                goto out;
-            }
+    /* 4..7 length of the table including header, in bytes (4 bytes) */
+    if (!has_header) {
+        if (!changed) {
+            fprintf(stderr,
+                    "warning: acpi table specified with data="
+                    " but no table headers are provided, defaults are used\n");
+        }
+    } else {
+        /* check if actual length is correct */
+        memcpy(&val32, f + ACPI_TABLE_LEN_OFF, ACPI_TABLE_LEN_SIZE);
+        val = le32_to_cpu(val32);
+        if (val != len) {
+            fprintf(stderr,
+                    "warning: acpi table specified with file= has wrong length,"
+                    " header says %lu, actual size %zu\n",
+                    val, len);
+            ++changed;
         }
-
-        close(fd);
-        if (!n)
-            break;
-        f = n + 1;
     }
-    if (off < length) {
-        /* don't pass random value in process to guest */
-        memset(p + off, 0, length - off);
+
+    /* fix table length */
+    /* we may avoid putting length here if has_header is true */
+    val32 = cpu_to_le32(len);
+    memcpy(f + ACPI_TABLE_LEN_OFF, &val32, ACPI_TABLE_LEN_SIZE);
+
+    /* 9 checksum (1 byte) */
+    /* we may as well leave checksum intact if has_header is true */
+    /* alternatively there may be a way to set cksum to a given value */
+    if (changed || !has_header || 1) {
+        f[ACPI_TABLE_CSUM_OFF] = 0;
+        f[ACPI_TABLE_CSUM_OFF] = acpi_checksum((uint8_t*)f, len);
     }
 
-    acpi_hdr_p = (struct acpi_table_header*)p;
-    acpi_hdr_p->length = cpu_to_le32(length);
-    acpi_hdr_p->checksum = acpi_checksum((uint8_t*)p, length);
     /* increase number of tables */
     (*(uint16_t*)acpi_tables) =
-	    cpu_to_le32(le32_to_cpu(*(uint16_t*)acpi_tables) + 1);
+        cpu_to_le16(le16_to_cpu(*(uint16_t*)acpi_tables) + 1);
     return 0;
+
 out:
-    if (acpi_tables) {
-        qemu_free(acpi_tables);
-        acpi_tables = NULL;
-    }
+    acpi_tables_len = start;
     return -1;
 }
