[sl] syslinux support (EXPERIMENTAL)

* MS platforms only (*BREAKS* MinGW)

src/syslinux/libinstaller/setadv.c

@@ -0,0 +1,166 @@
+/* ----------------------------------------------------------------------- *
+ *
+ *   Copyright 2007-2008 H. Peter Anvin - All Rights Reserved
+ *   Copyright 2010 Intel Corporation; author: H. Peter Anvin
+ *
+ *   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, Inc., 53 Temple Place Ste 330,
+ *   Boston MA 02111-1307, USA; either version 2 of the License, or
+ *   (at your option) any later version; incorporated herein by reference.
+ *
+ * ----------------------------------------------------------------------- */
+
+/*
+ * setadv.c
+ *
+ * (Over)write a data item in the auxilliary data vector.  To
+ * delete an item, set its length to zero.
+ *
+ * Return 0 on success, -1 on error, and set errno.
+ *
+ */
+#define  _GNU_SOURCE
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <string.h>
+#include <errno.h>
+#include "syslxint.h"
+
+unsigned char syslinux_adv[2 * ADV_SIZE];
+
+#define ADV_MAGIC1	0x5a2d2fa5	/* Head signature */
+#define ADV_MAGIC2	0xa3041767	/* Total checksum */
+#define ADV_MAGIC3	0xdd28bf64	/* Tail signature */
+
+static void cleanup_adv(unsigned char *advbuf)
+{
+    int i;
+    uint32_t csum;
+
+    /* Make sure both copies agree, and update the checksum */
+    set_32((uint32_t *) advbuf, ADV_MAGIC1);
+
+    csum = ADV_MAGIC2;
+    for (i = 8; i < ADV_SIZE - 4; i += 4)
+	csum -= get_32((uint32_t *) (advbuf + i));
+
+    set_32((uint32_t *) (advbuf + 4), csum);
+    set_32((uint32_t *) (advbuf + ADV_SIZE - 4), ADV_MAGIC3);
+
+    memcpy(advbuf + ADV_SIZE, advbuf, ADV_SIZE);
+}
+
+int syslinux_setadv(int tag, size_t size, const void *data)
+{
+    uint8_t *p;
+    size_t left;
+    uint8_t advtmp[ADV_SIZE];
+
+    if ((unsigned)tag - 1 > 254) {
+	errno = EINVAL;
+	return -1;		/* Impossible tag value */
+    }
+
+    if (size > 255) {
+	errno = ENOSPC;		/* Max 255 bytes for a data item */
+	return -1;
+    }
+
+    left = ADV_LEN;
+    p = advtmp;
+    memcpy(p, syslinux_adv + 2 * 4, left);	/* Make working copy */
+
+    while (left >= 2) {
+	uint8_t ptag = p[0];
+	size_t plen = p[1] + 2;
+
+	if (ptag == ADV_END)
+	    break;
+
+	if (ptag == tag) {
+	    /* Found our tag.  Delete it. */
+
+	    if (plen >= left) {
+		/* Entire remainder is our tag */
+		break;
+	    }
+	    memmove(p, p + plen, left - plen);
+	} else {
+	    /* Not our tag */
+	    if (plen > left)
+		break;		/* Corrupt tag (overrun) - overwrite it */
+
+	    left -= plen;
+	    p += plen;
+	}
+    }
+
+    /* Now (p, left) reflects the position to write in and how much space
+       we have for our data. */
+
+    if (size) {
+	if (left < size + 2) {
+	    errno = ENOSPC;	/* Not enough space for data */
+	    return -1;
+	}
+
+	*p++ = (uint8_t) tag;
+	*p++ = (uint8_t) size;
+	memcpy(p, data, size);
+	p += size;
+	left -= size + 2;
+    }
+
+    memset(p, 0, left);
+
+    /* If we got here, everything went OK, commit the write */
+    memcpy(syslinux_adv + 2 * 4, advtmp, ADV_LEN);
+    cleanup_adv(syslinux_adv);
+
+    return 0;
+}
+
+void syslinux_reset_adv(unsigned char *advbuf)
+{
+    /* Create an all-zero ADV */
+    memset(advbuf + 2 * 4, 0, ADV_LEN);
+    cleanup_adv(advbuf);
+}
+
+static int adv_consistent(const unsigned char *p)
+{
+    int i;
+    uint32_t csum;
+
+    if (get_32((uint32_t *) p) != ADV_MAGIC1 ||
+	get_32((uint32_t *) (p + ADV_SIZE - 4)) != ADV_MAGIC3)
+	return 0;
+
+    csum = 0;
+    for (i = 4; i < ADV_SIZE - 4; i += 4)
+	csum += get_32((uint32_t *) (p + i));
+
+    return csum == ADV_MAGIC2;
+}
+
+/*
+ * Verify that an in-memory ADV is consistent, making the copies consistent.
+ * If neither copy is OK, return -1 and call syslinux_reset_adv().
+ */
+int syslinux_validate_adv(unsigned char *advbuf)
+{
+    if (adv_consistent(advbuf + 0 * ADV_SIZE)) {
+	memcpy(advbuf + ADV_SIZE, advbuf, ADV_SIZE);
+	return 0;
+    } else if (adv_consistent(advbuf + 1 * ADV_SIZE)) {
+	memcpy(advbuf, advbuf + ADV_SIZE, ADV_SIZE);
+	return 0;
+    } else {
+	syslinux_reset_adv(advbuf);
+	return -1;
+    }
+}