diff --git a/hw/acpi.c b/hw/acpi.c
index ad40fb4..79ec66c 100644
--- a/hw/acpi.c
+++ b/hw/acpi.c
@@ -20,19 +20,30 @@
 #include "pc.h"
 #include "acpi.h"
 
-struct acpi_table_header
-{
-    char signature [4];    /* ACPI signature (4 ASCII characters) */
+struct acpi_table_header {
+    uint16_t _length;         /* our length, not actual part of the hdr */
+                              /* XXX why we have 2 length fields here? */
+    char sig[4];              /* ACPI signature (4 ASCII characters) */
     uint32_t length;          /* Length of table, in bytes, including header */
     uint8_t revision;         /* ACPI Specification minor version # */
     uint8_t checksum;         /* To make sum of entire table == 0 */
-    char oem_id [6];       /* OEM identification */
-    char oem_table_id [8]; /* OEM table identification */
+    char oem_id[6];           /* OEM identification */
+    char oem_table_id[8];     /* OEM table identification */
     uint32_t oem_revision;    /* OEM revision number */
-    char asl_compiler_id [4]; /* ASL compiler vendor ID */
+    char asl_compiler_id[4];  /* ASL compiler vendor ID */
     uint32_t asl_compiler_revision; /* ASL compiler revision number */
 } __attribute__((packed));
 
+#define ACPI_TABLE_HDR_SIZE sizeof(struct acpi_table_header)
+#define ACPI_TABLE_PFX_SIZE sizeof(uint16_t)  /* size of the extra prefix */
+
+static const char dfl_hdr[ACPI_TABLE_HDR_SIZE] =
+    "\0\0"                   /* fake _length (2) */
+    "QEMU\0\0\0\0\1\0"       /* sig (4), len(4), revno (1), csum (1) */
+    "QEMUQEQEMUQEMU\1\0\0\0" /* OEM id (6), table (8), revno (4) */
+    "QEMU\1\0\0\0"           /* ASL compiler ID (4), version (4) */
+    ;
+
 char *acpi_tables;
 size_t acpi_tables_len;
 
@@ -40,163 +51,198 @@ static int acpi_checksum(const uint8_t *data, int len)
 {
     int sum, i;
     sum = 0;
-    for(i = 0; i < len; i++)
+    for (i = 0; i < len; i++) {
         sum += data[i];
+    }
     return (-sum) & 0xff;
 }
 
+/* like strncpy() but zero-fills the tail of destination */
+static void strzcpy(char *dst, const char *src, size_t size)
+{
+    size_t len = strlen(src);
+    if (len >= size) {
+        len = size;
+    } else {
+      memset(dst + len, 0, size - len);
+    }
+    memcpy(dst, src, len);
+}
+
+/* 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;
     unsigned long val;
-    uint32_t length;
-    struct acpi_table_header *acpi_hdr_p;
-    size_t off;
+    size_t len, start, allen;
+    bool has_header;
+    int changed;
+    int r;
+    struct acpi_table_header hdr;
+
+    r = 0;
+    r |= get_param_value(buf, sizeof(buf), "data", t) ? 1 : 0;
+    r |= get_param_value(buf, sizeof(buf), "file", t) ? 2 : 0;
+    switch (r) {
+    case 0:
+        buf[0] = '\0';
+        /* fallthrough for default behavior */
+    case 1:
+        has_header = false;
+        break;
+    case 2:
+        has_header = true;
+        break;
+    default:
+        fprintf(stderr, "acpitable: both data and file are specified\n");
+        return -1;
+    }
 
-    memset(&acpi_hdr, 0, sizeof(acpi_hdr));
-  
-    if (get_param_value(buf, sizeof(buf), "sig", t)) {
-        strncpy(acpi_hdr.signature, buf, 4);
+    if (!acpi_tables) {
+        allen = sizeof(uint16_t);
+        acpi_tables = qemu_mallocz(allen);
     } else {
-        strncpy(acpi_hdr.signature, dfl_id, 4);
+        allen = acpi_tables_len;
     }
+
+    start = allen;
+    acpi_tables = qemu_realloc(acpi_tables, start + ACPI_TABLE_HDR_SIZE);
+    allen += has_header ? ACPI_TABLE_PFX_SIZE : 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));
+            return -1;
+        }
+
+        for (;;) {
+            char data[8192];
+            r = read(fd, data, sizeof(data));
+            if (r == 0) {
+                break;
+            } else if (r > 0) {
+                acpi_tables = qemu_realloc(acpi_tables, allen + r);
+                memcpy(acpi_tables + allen, data, r);
+                allen += r;
+            } else if (errno != EINTR) {
+                fprintf(stderr, "can't read file %s: %s\n",
+                        f, strerror(errno));
+                close(fd);
+                return -1;
+            }
+        }
+
+        close(fd);
+    }
+
+    /* now fill in the header fields */
+
+    f = acpi_tables + start;   /* start of the table */
+    changed = 0;
+
+    /* copy the header to temp place to align the fields */
+    memcpy(&hdr, has_header ? f : dfl_hdr, ACPI_TABLE_HDR_SIZE);
+
+    /* length of the table minus our prefix */
+    len = allen - start - ACPI_TABLE_PFX_SIZE;
+
+    hdr._length = cpu_to_le16(len);
+
+    if (get_param_value(buf, sizeof(buf), "sig", t)) {
+        strzcpy(hdr.sig, buf, sizeof(hdr.sig));
+        ++changed;
+    }
+
+    /* length of the table including header, in bytes */
+    if (has_header) {
+        /* check if actual length is correct */
+        val = le32_to_cpu(hdr.length);
+        if (val != len) {
+            fprintf(stderr,
+                "warning: acpitable has wrong length,"
+                " header says %lu, actual size %zu bytes\n",
+                val, len);
+            ++changed;
+        }
+    }
+    /* we may avoid putting length here if has_header is true */
+    hdr.length = cpu_to_le32(len);
+
     if (get_param_value(buf, sizeof(buf), "rev", t)) {
-        val = strtoul(buf, &p, 10);
-        if (val > 255 || *p != '\0')
-            goto out;
-    } else {
-        val = 1;
+        val = strtoul(buf, &p, 0);
+        if (val > 255 || *p) {
+            fprintf(stderr, "acpitable: \"rev=%s\" is invalid\n", buf);
+            return -1;
+        }
+        hdr.revision = (uint8_t)val;
+        ++changed;
     }
-    acpi_hdr.revision = (int8_t)val;
 
     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);
+        strzcpy(hdr.oem_id, buf, sizeof(hdr.oem_id));
+        ++changed;
     }
 
     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);
+        strzcpy(hdr.oem_table_id, buf, sizeof(hdr.oem_table_id));
+        ++changed;
     }
 
     if (get_param_value(buf, sizeof(buf), "oem_rev", t)) {
-        val = strtol(buf, &p, 10);
-        if(*p != '\0')
-            goto out;
-    } else {
-        val = 1;
+        val = strtol(buf, &p, 0);
+        if (*p) {
+            fprintf(stderr, "acpitable: \"oem_rev=%s\" is invalid\n", buf);
+            return -1;
+        }
+        hdr.oem_revision = cpu_to_le32(val);
+        ++changed;
     }
-    acpi_hdr.oem_revision = cpu_to_le32(val);
 
     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);
+        strzcpy(hdr.asl_compiler_id, buf, sizeof(hdr.asl_compiler_id));
+        ++changed;
     }
 
     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));
-            goto out;
+        val = strtol(buf, &p, 0);
+        if (*p) {
+            fprintf(stderr, "acpitable: \"%s=%s\" is invalid\n",
+                    "asl_compiler_rev", buf);
+            return -1;
         }
-        length += s.st_size;
-        if (!n)
-            break;
-        *n = ':';
-        f = n + 1;
+        hdr.asl_compiler_revision = cpu_to_le32(val);
+        ++changed;
     }
 
-    if (!acpi_tables) {
-        acpi_tables_len = sizeof(uint16_t);
-        acpi_tables = qemu_mallocz(acpi_tables_len);
+    if (!has_header && !changed) {
+        fprintf(stderr, "warning: acpitable: no table headers are specified\n");
     }
-    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;
-            }
-        }
 
-        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);
+    /* now calculate checksum of the table, complete with the header */
+    /* 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 */
+    hdr.checksum = 0;    /* for checksum calculation */
+
+    /* put header back */
+    memcpy(f, &hdr, sizeof(hdr));
+
+    if (changed || !has_header || 1) {
+        ((struct acpi_table_header *)f)->checksum =
+            acpi_checksum((uint8_t *)f + ACPI_TABLE_PFX_SIZE, 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);
+    (*(uint16_t *)acpi_tables) =
+        cpu_to_le32(le32_to_cpu(*(uint16_t *)acpi_tables) + 1);
+
+    acpi_tables_len = allen;
     return 0;
-out:
-    if (acpi_tables) {
-        qemu_free(acpi_tables);
-        acpi_tables = NULL;
-    }
-    return -1;
+
 }
 
 /* ACPI PM1a EVT */
diff --git a/qemu-options.hx b/qemu-options.hx
index 1d57f64..74c0edb 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -1062,12 +1062,17 @@ Enable virtio balloon device (default), optionally with PCI address
 ETEXI
 
 DEF("acpitable", HAS_ARG, QEMU_OPTION_acpitable,
-    "-acpitable [sig=str][,rev=n][,oem_id=str][,oem_table_id=str][,oem_rev=n][,asl_compiler_id=str][,asl_compiler_rev=n][,data=file1[:file2]...]\n"
+    "-acpitable [sig=str][,rev=n][,oem_id=str][,oem_table_id=str][,oem_rev=n][,asl_compiler_id=str][,asl_compiler_rev=n][,{data|file}=file1[:file2]...]\n"
     "                ACPI table description\n", QEMU_ARCH_I386)
 STEXI
 @item -acpitable [sig=@var{str}][,rev=@var{n}][,oem_id=@var{str}][,oem_table_id=@var{str}][,oem_rev=@var{n}] [,asl_compiler_id=@var{str}][,asl_compiler_rev=@var{n}][,data=@var{file1}[:@var{file2}]...]
 @findex -acpitable
 Add ACPI table with specified header fields and context from specified files.
+For file=, take whole ACPI table from the specified files, including all
+ACPI headers (possible overridden by other options).
+For data=, only data
+portion of the table is used, all header information is specified in the
+command line.
 ETEXI
 
 DEF("smbios", HAS_ARG, QEMU_OPTION_smbios,
