Re: git: 46ea2ffc3fbc - main - stand: Reduce limit to 500k for x86 loader

On Thu, Aug 01, 2024 at 09:31:24PM +0000, Warner Losh wrote:
> The branch main has been updated by imp:
> 
> URL: https://cgit.FreeBSD.org/src/commit/?id=46ea2ffc3fbc42089d8322a65fdee8476d2b00d6
> 
> commit 46ea2ffc3fbc42089d8322a65fdee8476d2b00d6
> Author:     Warner Losh <imp@FreeBSD.org>
> AuthorDate: 2024-08-01 21:24:51 +0000
> Commit:     Warner Losh <imp@FreeBSD.org>
> CommitDate: 2024-08-01 21:30:26 +0000
> 
>     stand: Reduce limit to 500k for x86 loader
>     
>     The largest loader that works for PXE boot is about 500k. PXE needs low
>     memory for packets and other driver state, so the largest safe size for
>     the loader is about 500k. Reduce the size from 560k to 500k so we don't
>     accidentally break PXE in the future.
>     
>     Add a comment for people with special needs. If you control the
>     hardware, it can be safe to have boot loaders as large as 580k or 600k
>     in some cases. Since the BIOS loader is becoming more and more of a
>     legacy item, the build variable LOADERSIZE isn't documented. This change
>     doesn't change that: there's been little demand for this documentation
>     and in general, users shouldn't change it lightly.
>     
>     PR: 257018
>     Sponsored by: Netflix
> ---
>  stand/i386/loader/Makefile | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/stand/i386/loader/Makefile b/stand/i386/loader/Makefile
> index a4aa3a3c4d45..efd442977780 100644
> --- a/stand/i386/loader/Makefile
> +++ b/stand/i386/loader/Makefile
> @@ -32,7 +32,12 @@ VERSION_FILE=	${.CURDIR}/../loader/version
>  #
>  # will tell you how many kiB of lomem are available.
>  #
> -LOADERSIZE?=	560000		# Largest known safe size for loader.bin
> +# We further reduce this to 500k, though, to give PXE an additional 64k of space
> +# so pxeloader will fit. If you have special needs that do not include pxeboot,
> +# you can safely set this as high as 560000 generally, or a bit higher if you
> +# have tight control over the machines you are booting on.
> +#
> +LOADERSIZE?=	500000		# Largest known safe size for loader.bin

Hi Warner,

This breaks the WITH_BEARSSL (which implies WITH_LOADER_VERIEXEC) build.
When enabled, the loader ends up being just slightly larger than the
limit.