On Tue, Apr 24, 2018 at 04:08:57PM -0700, Andrew Jeddeloh wrote: > Thanks for the reply. > > I'm not sure I follow. Looking over the 32 bit boot spec, it looks > like the process is: > > 1) zero out linux_params > - grub does this > 2) copy the linux boot params (from 0x1f1) into linux params > - grub does this by reading from 0x0 until the end of lh, then > copying lh+0x1f1 til the end of lh into linux_headers [4][5] > 3) Do the read/write/modify operations that would happen for a 16 bit boot > 4) calculate the end of the the setup header > - grub does not do this and I think assumes its just the end of the > linux_params struct
As Michael said, "0x0202 + byte value at offset 0x0201" is your friend. > 5) fill out the rest of the setup header things from the zero page doc [6] > - AFAICT this isn't meant to be read from the kernel image, but > instead filled out by bootloader or left as zero AIUI it is. Please look above. > - It looks like the current code is trying to do this but is just > assuming the end is at the end of linux_params. This is wrong due to grub_e820_mmap. > - Looking over the items in the zero page doc, there doesn't seem to > be anything that the kernel could supply a useful "default" value. GRUB have to load the rest of Linux header into linux_params. Current math is wrong and have to be fixed. Please look above and think about newer versions of Linux headers which GRUB is not aware of. > As I understand it, the read is not harmful (as it just gets > overwritten by the bootloader later) but also not needed. Is this your > understanding? This read is needed, however, math has to be fixed. Additionally, I think that you can take a look at SYSLINUX and do something similar in GRUB. > I'll definitely submit a patch upstream once I figure out what should > be going on. Great! Thanks! Daniel _______________________________________________ Grub-devel mailing list Grub-devel@gnu.org https://lists.gnu.org/mailman/listinfo/grub-devel
