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authorWarner Losh <imp@FreeBSD.org>2022-08-11 03:19:01 +0000
committerWarner Losh <imp@FreeBSD.org>2022-08-11 03:29:20 +0000
commit39fdad34e220c52a433e78f20c8c39412429014e (patch)
tree3578f0850223d0f87e89a4c215ffe20d2edd8626 /sys/cddl/contrib/opensolaris/uts/common/os/list.c
parente2295b9117233d8248fe919c6b28ef1d44a8950d (diff)
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stand: impose 510,000 byte limit for /boot/loader and /boot/pxeldrHEADmain
The BIOS method of booting imposes an absolute limit of 640k for the size of the program being run due to btx. In practice, this means that programs larger than about 500kiB will fail in odd ways as the stack / heap will overflow. Pick 510,000 as the cutoff line semi-arbitrarily. loader_lua is now almost too big and we want to break the build when it crosses this threshold. In my experience, below 500,000 always works, above 520,000 always seems to fail with things getting bad somewhere between 512,000 to 515,000. 510,000 is as close to the line as I think we can go, though experience may dictate we need to lower this in the future. This is at-best a stop-breakage until we have a better way to subset the boot loader for BIOS booting to allow better, more fined-tuned /boot/loaders for the many different environments they have to run in. This likely means we'll have a graphical loader than understands a few filesystmes for installation, and a non-graphical loader that understands the most filesystems possible for everything else in the future. Our build infrastructure needs some work before we can do that, however. At this late date, it likely isn't worth the efforts to move parts of the loader into high memory. There's a number of assumptions about where the stack is, where buffers reside, etc that are fulfilled when it lives in the first 640k that would need bounce buffers and/or other counter measures if we were to split it up. All BIOS calls are done in 16-bit mode with SEG:OFF addresses, requiring them to be in the first 640k of RAM. And nearly all machines in the last decade can boot with UEFI (though there's some exceptions, so it isn't worth killing outright yet). Sponsored by: Netflix Reviewed by: kevans Differential Revision: https://reviews.freebsd.org/D36129
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