From 9c239053045568abf960b01e4eb2c7205e3cd7d6 Mon Sep 17 00:00:00 2001 From: Sam Ravnborg Date: Tue, 4 Jan 2011 11:39:13 +0000 Subject: [PATCH] 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 Signed-off-by: David S. Miller --- arch/sparc/boot/piggyback_32.c | 23 +++++++++++++++++++++-- 1 file 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)