David Woodhouse 99f857db88 x86, build: Dynamically find entry points in compressed startup code ... We have historically hard-coded entry points in head.S just so it's easy to build the executable/bzImage headers with references to them. Unfortunately, this leads to boot loaders abusing these "known" addresses even when they are *explicitly* told that they "should look at the ELF header to find this address, as it may change in the future". And even when the address in question *has* actually been changed in the past, without fanfare or thought to compatibility. Thus we have bootloaders doing stunningly broken things like jumping to offset 0x200 in the kernel startup code in 64-bit mode, *hoping* that startup_64 is still there (it has moved at least once before). And hoping that it's actually a 64-bit kernel despite the fact that we don't give them any indication of that fact. This patch should hopefully remove the temptation to abuse internal addresses in future, where sternly worded comments have not sufficed. Instead of having hard-coded addresses and saying "please don't abuse these", we actually pull the addresses out of the ELF payload into zoffset.h, and make build.c shove them back into the right places in the bzImage header. Rather than including zoffset.h into build.c and thus having to rebuild the tool for every kernel build, we parse it instead. The parsing code is small and simple. This patch doesn't actually move any of the interesting entry points, so any offending bootloader will still continue to "work" after this patch is applied. For some version of "work" which includes jumping into the compressed payload and crashing, if the bzImage it's given is a 32-bit kernel. No change there then. [ hpa: some of the issues in the description are addressed or retconned by the 2.12 boot protocol. This patch has been edited to only remove fixed addresses that were *not* thus retconned. ] Signed-off-by: David Woodhouse <David.Woodhouse@intel.com> Link: http://lkml.kernel.org/r/1358513837.2397.247.camel@shinybook.infradead.org Signed-off-by: H. Peter Anvin <hpa@linux.intel.com> Cc: Matt Fleming <matt.fleming@intel.com>		2013-01-27 20:19:37 -08:00
..
.gitignore	i386: move boot	2007-10-11 11:16:41 +02:00
build.c	x86, build: Dynamically find entry points in compressed startup code	2013-01-27 20:19:37 -08:00