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authorSam Ravnborg <sam@ravnborg.org>2011-01-04 11:39:13 +0000
committerDavid S. Miller <davem@davemloft.net>2011-01-04 19:25:04 -0800
commit9c239053045568abf960b01e4eb2c7205e3cd7d6 (patch)
tree18ff36b9a58c0c4dded3d7a4097ea4e5ca1fa8fc /arch/sparc/boot
parentb2a39b0d8ec2ce2bdcff4e01572b4e885220254d (diff)
downloadlinux-9c239053045568abf960b01e4eb2c7205e3cd7d6.tar.gz
sparc: additional comments to piggyback_32.c
While reverse engineering the functionality of piggyback I missed that the code was actually commented. So I added a few comments. Signed-off-by: Sam Ravnborg <sam@ravnborg.org> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'arch/sparc/boot')
-rw-r--r--arch/sparc/boot/piggyback_32.c23
1 files changed, 21 insertions, 2 deletions
diff --git a/arch/sparc/boot/piggyback_32.c b/arch/sparc/boot/piggyback_32.c
index 5c86a7d03b6f..5e856f2e9e0f 100644
--- a/arch/sparc/boot/piggyback_32.c
+++ b/arch/sparc/boot/piggyback_32.c
@@ -36,6 +36,8 @@
* as PROM looks for a.out image only.
*/
+#define AOUT_TEXT_OFFSET 32
+
/* read two bytes as big endian */
static unsigned short ld2(char *p)
{
@@ -154,12 +156,20 @@ int main(int argc,char **argv)
die(argv[1]);
j = 0;
} else if (memcmp(buffer, aout_magic, 4) == 0) {
- i = j = 32;
+ i = j = AOUT_TEXT_OFFSET;
} else {
fprintf (stderr, "Not ELF nor a.out. Don't blame me.\n");
exit(1);
}
k = i;
+ /*
+ * We need to fill in values for sparc_ramdisk_image + sparc_ramdisk_size
+ * To locate these symbols search for the "HdrS" text which appear
+ * in the image a little before the gokernel symbol.
+ * See definition of these in init_32.S
+ */
+
+ /* Find the gokernel label */
i += (ld2(buffer + j + 2) << 2) - 512;
if (lseek(image, i, 0) < 0)
die("lseek");
@@ -177,6 +187,13 @@ int main(int argc,char **argv)
if (lseek(image, offset, 0) < 0)
die("lseek");
+ /*
+ * root_flags = 0
+ * root_dev = 1 (RAMDISK_MAJOR)
+ * ram_flags = 0
+ * sparc_ramdisk_image = "PAGE aligned address after _end")
+ * sparc_ramdisk_size = size of image
+ */
st4(buffer, 0);
st4(buffer + 4, 0x01000000);
st4(buffer + 8, (end + 32 + 4095) & ~4095);
@@ -184,11 +201,13 @@ int main(int argc,char **argv)
if (write(image, buffer + 2, 14) != 14)
die(argv[1]);
+
+ /* seek page aligned boundary in the image file and add boot image */
if (lseek(image, k - start + ((end + 32 + 4095) & ~4095), 0) < 0)
die("lseek");
if ((tail = open(argv[3],O_RDONLY)) < 0)
die(argv[3]);
- while ((i = read (tail, buffer, 1024)) > 0)
+ while ((i = read(tail, buffer, 1024)) > 0)
if (write(image, buffer, i) != i)
die(argv[1]);
if (close(image) < 0)