Re: kern/54560 (PXE netboot regression)

[Andreas Gustafsson <gson%gson.org@localhost>]

The following reply was made to PR kern/54560; it has been noted by GNATS.

From: Andreas Gustafsson <gson%gson.org@localhost>
To: manu%netbsd.org@localhost (Emmanuel Dreyfus)
Cc: gnats-bugs%netbsd.org@localhost
Subject: Re: kern/54560 (PXE netboot regression)
Date: Tue, 24 Sep 2019 12:25:02 +0300

 Emmanuel Dreyfus wrote:
 > I am not sure there are real multiboot + PXE usage. Perhaps we can just
 > disable multiboot 2 for PXE without looking further into what the
 > problem actually is.
 > 
 > In case you ar ecurious and want to look into it further, my first hunch
 > is that the multiboot 2 code increases the pxeboot_ia32.bin file beyond
 > 64kB. You can easily test if this is the problem, remove CPPFLAGS+=
 > -DNO_MULTIBOOT2 and instead add
 > 
 > CPPFLAGS+= -DNO_GPT 
 > CPPFLAGS+= -DNO_RAIDFRAME
 > 
 > You will get a pxeboot_ia32.bin below 64 kB with multiboot 2 enabled. If
 > that boots, then we have our answer.
 
 That did not boot, but your hunch may be correct anyway.  Here's a
 summary of my test results, with the size of pxeboot_ia32.bin in each:
 
 Source date          CPPFLAGS                     Size      Result
 ==================================================================
 2019.09.13.01.34.19  none                         61664     pass
 2019.09.13.05.13.54  none                         73952     fail
 2019.09.22.18.31.59  -DNO_MULTIBOOT2              61664     pass
 2019.09.21.15.56.09  -DNO_GPT -DNO_RAIDFRAME      65760     fail
 
 That is, the test failed when and only when pxeboot_ia32.bin was
 larger than 65536 bytes.
 
 I guess the next question is, why does multiboot 2 use more space
 than GPT and raidframe combined?
 -- 
 Andreas Gustafsson, gson%gson.org@localhost