[syslinux:master] chain.c32: add grubcfg= for passing an alternative config filename to GRUB Legacy and cleanup the root partition passing
syslinux-bot for Gert Hulselmans
gerth at zytor.com
Mon Jul 5 16:06:03 PDT 2010
Commit-ID: 601712aef7489e68d372a8b7290959a572cb67a3
Gitweb: http://syslinux.zytor.com/commit/601712aef7489e68d372a8b7290959a572cb67a3
Author: Gert Hulselmans <gerth at zytor.com>
AuthorDate: Sun, 4 Jul 2010 20:35:15 +0200
Committer: Gert Hulselmans <gerth at zytor.com>
CommitDate: Sun, 4 Jul 2010 20:35:15 +0200
chain.c32: add grubcfg= for passing an alternative config filename to GRUB Legacy and cleanup the root partition passing
GRUB Legacy reserves 89 bytes for storing the filename of the configfile
from memory address 0x8217 to 0x826f.
We allow overwriting the default value (/boot/grub/menu.lst) when
grubcfg=<filename> is used together with grub=<loader>.
Examples:
chain.c32 fs grub=/boot/grub/stage2 grubcfg=/boot/grub/grub.lst
chain.c32 hd1,10 grub=/boot/grub/stage2 grubcfg=/boot/grub/grub.lst
Use a structure instead of hard-coded offsets for modifying the install_partition variable
(and the configfile name) in the stage2 file.
Add some comments about the "boot information format" of the Multiboot specification, which
is very similar to the install_partition variable used by GRUB Legacy.
Signed-off-by: Gert Hulselmans <gerth at zytor.com>
---
com32/modules/chain.c | 121 +++++++++++++++++++++++++++++++++++++++++++++----
1 files changed, 112 insertions(+), 9 deletions(-)
diff --git a/com32/modules/chain.c b/com32/modules/chain.c
index 4f5baf1..7a2c8d4 100644
--- a/com32/modules/chain.c
+++ b/com32/modules/chain.c
@@ -78,7 +78,11 @@
*
* grub=<loader>
* same as seg=0x800 file=<loader> & jumping to seg 0x820,
- * used with GRUB stage2 files.
+ * used with GRUB Legacy stage2 files.
+ *
+ * grubcfg=<filename>
+ * set an alternative config filename in stage2 of Grub Legacy,
+ * only applicable in combination with "grub=<loader>".
*
* grldr=<loader>
* pass the partition number to GRUB4DOS,
@@ -125,6 +129,7 @@ static struct options {
bool cmldr;
bool grub;
bool grldr;
+ const char *grubcfg;
bool swap;
bool hide;
bool sethidden;
@@ -1276,7 +1281,8 @@ Options: file=<loader> Load and execute file, instead of boot sector\n\
freedos=<loader> Load FreeDOS KERNEL.SYS\n\
msdos=<loader> Load MS-DOS IO.SYS\n\
pcdos=<loader> Load PC-DOS IBMBIO.COM\n\
- grub=<loader> Load GRUB stage2\n\
+ grub=<loader> Load GRUB Legacy stage2\n\
+ grubcfg=<filename> Set alternative config filename for GRUB Legacy\n\
grldr=<loader> Load GRUB4DOS grldr\n\
seg=<segment> Jump to <seg>:0000, instead of 0000:7C00\n\
swap Swap drive numbers, if bootdisk is not fd0/hd0\n\
@@ -1349,6 +1355,8 @@ int main(int argc, char *argv[])
opt.seg = 0x800; /* stage2 wants this address */
opt.loadfile = argv[i] + 5;
opt.grub = true;
+ } else if (!strncmp(argv[i], "grubcfg=", 8)) {
+ opt.grubcfg = argv[i] + 8;
} else if (!strncmp(argv[i], "grldr=", 6)) {
opt.loadfile = argv[i] + 6;
opt.grldr = true;
@@ -1392,6 +1400,11 @@ int main(int argc, char *argv[])
}
}
+ if (opt.grubcfg && !opt.grub) {
+ error("grubcfg=<filename> must be used together with grub=<loader>.\n");
+ goto bail;
+ }
+
if (opt.seg) {
regs.es = regs.cs = regs.ss = regs.ds = regs.fs = regs.gs = opt.seg;
} else {
@@ -1583,15 +1596,105 @@ int main(int argc, char *argv[])
}
if (opt.grub) {
- regs.ip = 0x200; /* jump 0x200 bytes into the loadfile */
+ /* Layout of stage2 file (from byte 0x0 to 0x270) */
+ struct grub_stage2_patch_area {
+ /* 0x0 to 0x205 */
+ char unknown[0x206];
+ /* 0x206: compatibility version number major */
+ uint8_t compat_version_major;
+ /* 0x207: compatibility version number minor */
+ uint8_t compat_version_minor;
+
+ /* 0x208: install_partition variable */
+ struct {
+ /* 0x208: sub-partition in sub-partition part2 */
+ uint8_t part3;
+ /* 0x209: sub-partition in top-level partition */
+ uint8_t part2;
+ /* 0x20a: top-level partiton number */
+ uint8_t part1;
+ /* 0x20b: BIOS drive number (must be 0) */
+ uint8_t drive;
+ } __attribute__ ((packed)) install_partition;
+
+ /* 0x20c: deprecated (historical reason only) */
+ uint32_t saved_entryno;
+ /* 0x210: stage2_ID: will always be STAGE2_ID_STAGE2 = 0 in stage2 */
+ uint8_t stage2_id;
+ /* 0x211: force LBA */
+ uint8_t force_lba;
+ /* 0x212: version string (will probably be 0.97) */
+ char version_string[5];
+ /* 0x217: config filename */
+ char config_file[89];
+ /* 0x270: start of code (after jump from 0x200) */
+ char codestart[1];
+ } __attribute__ ((packed));
+
+ if (data[ndata].size < sizeof(struct grub_stage2_patch_area)) {
+ error
+ ("The file specified by grub=<loader> is to small to be stage2 of GRUB Legacy.\n");
+ goto bail;
+ }
+
+ struct grub_stage2_patch_area *stage2 = data[ndata].data;
- /* GRUB's stage2 wants the partition number in the install_partition
- * variable, located at memory address 0x8208.
- * We only need to change the value of memory address 0x820a too:
- * -1: whole drive (default)
+ /*
+ * Check the compatibility version number to see if we loaded a real
+ * stage2 file or a stage2 file that we support.
+ */
+ if (stage2->compat_version_major != 3
+ || stage2->compat_version_minor != 2) {
+ error
+ ("The file specified by grub=<loader> is not a supported stage2 GRUB Legacy binary\n");
+ goto bail;
+ }
+
+ /* jump 0x200 bytes into the loadfile */
+ regs.ip = 0x200;
+
+ /*
+ * GRUB Legacy wants the partition number in the install_partition
+ * variable, located at offset 0x208 of stage2.
+ * When GRUB Legacy is loaded, it is located at memory address 0x8208.
+ *
+ * It looks very similar to the "boot information format" of the
+ * Multiboot specification:
+ * http://www.gnu.org/software/grub/manual/multiboot/multiboot.html#Boot-information-format
+ *
+ * 0x208 = part3: sub-partition in sub-partition part2
+ * 0x209 = part2: sub-partition in top-level partition
+ * 0x20a = part1: top-level partition number
+ * 0x20b = drive: BIOS drive number (must be 0)
+ *
+ * GRUB Legacy doesn't store the BIOS drive number at 0x20b, but at
+ * another location.
+ *
+ * Partition numbers always start from zero.
+ * Unused partition bytes must be set to 0xFF.
+ *
+ * We only care about top-level partition, so we only need to change
+ * "part1" to the appropriate value:
+ * -1: whole drive (default) (-1 = 0xFF)
* 0-3: primary partitions
- * 4-*: logical partitions */
- ((uint8_t*) data[ndata].data)[0x20a] = (uint8_t)(whichpart - 1);
+ * 4-*: logical partitions
+ */
+ stage2->install_partition.part1 = whichpart - 1;
+
+ /*
+ * Grub Legacy reserves 89 bytes (from 0x8217 to 0x826f) for the
+ * config filename. The filename passed via grubcfg= will overwrite
+ * the default config filename "/boot/grub/menu.lst".
+ */
+ if (opt.grubcfg) {
+ if (strlen(opt.grubcfg) > sizeof(stage2->config_file) - 1) {
+ error
+ ("The config filename length can't exceed 88 characters.\n");
+ goto bail;
+ }
+
+ strcpy((char *)stage2->config_file, opt.grubcfg);
+ }
}
ndata++;
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