Messages in this thread | | | Date | Thu, 27 Mar 2008 10:46:48 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH -mm 0/4] x86_64 boot: Add linked listof struct setup_data to boot protocol |
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* Paul Jackson <pj@sgi.com> wrote:
> Ingo wrote: > > stupidly shortsighted limit ... > > Eh ... I don't think all that shortsighted ... that 4096 limit has > probably been around longer than Linux. Linus or hpa or others would > know the history better than I do.
the limit for boot parameters is 2048 bytes - the BUILD_WARN_ON() checks for the sum of the two boot parameter areas. We used empty_zero_page for boot parameter passing for a near eternity - 2K for the command line (which used to be clipped - recently upped to true 2048), and 2K for the boot parameters.
As a historic/nostalgic sidenote: the 2048 limit is not as old as Linux, version 0.11 of Linux had 512 bytes of special area for boot parameters, at 0x90000-0x901FF.
having fixed-length 2K buffering ABI between two historically rather inflexible pieces of software (the bootloader and the kernel), at a very fragile and under-capable junction of our bootstrap (very early during bootup) _is_ shortsighted. Granted, it's a difficult area to change but still it's a nasty limit - as you have found it out first-hand ;-)
Ingo
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