Re: git: 39fdad34e220 - main - stand: impose 510,000 byte limit for /boot/loader and /boot/pxeldr

In reply to: FreeBSD User : "Re: git: 39fdad34e220 - main - stand: impose 510,000 byte limit for /boot/loader and /boot/pxeldr"
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From: Warner Losh <imp_at_bsdimp.com>
Date: Thu, 11 Aug 2022 18:45:47 UTC
On Thu, Aug 11, 2022 at 12:43 PM FreeBSD User <freebsd@walstatt-de.de>
wrote:

> Am Thu, 11 Aug 2022 12:23:59 -0600
> Warner Losh <imp@bsdimp.com> schrieb:
>
> > On Thu, Aug 11, 2022 at 12:22 PM FreeBSD User <freebsd@walstatt-de.de>
> > wrote:
> >
> > > Am Thu, 11 Aug 2022 03:31:36 GMT
> > > Warner Losh <imp@FreeBSD.org> schrieb:
> > >
> > > > The branch main has been updated by imp:
> > > >
> > > > URL:
> > >
> https://cgit.FreeBSD.org/src/commit/?id=39fdad34e220c52a433e78f20c8c39412429014e
>
> > > >
> > > > commit 39fdad34e220c52a433e78f20c8c39412429014e
> > > > Author:     Warner Losh <imp@FreeBSD.org>
> > > > AuthorDate: 2022-08-11 03:19:01 +0000
> > > > Commit:     Warner Losh <imp@FreeBSD.org>
> > > > CommitDate: 2022-08-11 03:29:20 +0000
> > > >
> > > >     stand: impose 510,000 byte limit for /boot/loader and
> /boot/pxeldr
> > > >
> > > >     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
> > > > ---
> > > >  stand/i386/loader/Makefile | 5 +++++
> > > >  stand/i386/pxeldr/Makefile | 3 +++
> > > >  2 files changed, 8 insertions(+)
> > > >
> > > > diff --git a/stand/i386/loader/Makefile b/stand/i386/loader/Makefile
> > > > index 3685281ffd2c..cde1513aac06 100644
> > > > --- a/stand/i386/loader/Makefile
> > > > +++ b/stand/i386/loader/Makefile
> > > > @@ -19,6 +19,8 @@ PROG=               ${LOADER}.sym
> > > >  INTERNALPROG=
> > > >  NEWVERSWHAT?=        "bootstrap loader" x86
> > > >  VERSION_FILE=        ${.CURDIR}/../loader/version
> > > > +LOADERSIZE=  510000          # Largest known safe size
> > > > +
> > > >
> > > >  .PATH:               ${BOOTSRC}/i386/loader
> > > >
> > > > @@ -79,9 +81,12 @@ CFLAGS+=   -I${BOOTSRC}/i386
> > > >  8x16.c: ${SRCTOP}/contrib/terminus/ter-u16b.bdf
> > > >       vtfontcvt -f compressed-source -o ${.TARGET} ${.ALLSRC}
> > > >
> > > > +
> > > >  ${LOADER}: ${LOADER}.bin ${BTXLDR} ${BTXKERN}
> > > >       btxld -v -f elf -e ${LOADER_ADDRESS} -o ${.TARGET} -l
> ${BTXLDR} \
> > > >               -b ${BTXKERN} ${LOADER}.bin
> > > > +     @set -- `${SIZE} ${.TARGET} | tail -1` ;
> > > x=$$((${LOADERSIZE}-$$4)); \
> > > > +         echo "$$x bytes available"; test $$x -ge 0
> > > >
> > > >  ${LOADER}.bin: ${LOADER}.sym
> > > >       ${STRIPBIN} -R .comment -R .note -o ${.TARGET} ${.ALLSRC}
> > > > diff --git a/stand/i386/pxeldr/Makefile b/stand/i386/pxeldr/Makefile
> > > > index a44dc0de2885..f8bc1eae9a31 100644
> > > > --- a/stand/i386/pxeldr/Makefile
> > > > +++ b/stand/i386/pxeldr/Makefile
> > > > @@ -13,6 +13,7 @@ BOOT=       pxeboot
> > > >  LDR= pxeldr
> > > >  ORG= 0x7c00
> > > >  LOADER=      loader
> > > > +PXELDRSIZE= 510000           # Largest known safe size
> > > >
> > > >  .if defined(BOOT_PXELDR_PROBE_KEYBOARD)
> > > >  CFLAGS+=-DPROBE_KEYBOARD
> > > > @@ -41,5 +42,7 @@ CLEANFILES+= ${LOADER}
> > > >  ${LOADER}: ${LOADERBIN} ${BTXLDR} ${BTXKERN}
> > > >       btxld -v -f elf -e ${LOADER_ADDRESS} -o ${.TARGET} -l
> ${BTXLDR} \
> > > >           -b ${BTXKERN} ${LOADERBIN}
> > > > +     @set -- `${SIZE} ${.TARGET} | tail -1` ;
> > > x=$$((${PXELDRSIZE}-$$4)); \
> > > > +         echo "$$x bytes available"; test $$x -ge 0
> > > >
> > > >  .include <bsd.prog.mk>
> > > >
> > >
> > > On recent CURRENT (FreeBSD 14.0-CURRENT #10 main-n257258-348164aa9e5d:
> Wed
> > > Aug 10 22:39:17
> > > CEST 2022 amd64), buildworld fails here on several boxes:
> > >
> > > [...]
> > >
> > > ===> lib/flua/libjail (all)
> > > --- all_subdir_stand ---
> > > --- loader ---
> > > btxld -v -f elf -e 0x200000 -o loader -l
> > > /usr/obj/usr/src/amd64.amd64/stand/i386/btx/btxldr/btxldr  -b
> > > /usr/obj/usr/src/amd64.amd64/stand/i386/btx/btx/btx
> > > /usr/obj/usr/src/amd64.amd64/stand/i386/loader_lua/loader_lua.bin
> kernel:
> > > ver=1.02 size=690
> > > load=9000 entry=9010 map=16M pgctl=0:84 client: fmt=elf size=8a3f0
> > > text=836bc data=5238
> > > bss=8070 entry=0 output: fmt=elf size=8ae39 text=289 data=8aa80
> org=200000
> > > entry=200000
> > > -58585 bytes available 6.64 real
> > > 8.48 user         2.84 sys
> > >
> >
> > I'm sorry, but however you are building /boot/loader, it won't work when
> > it's that big. What are your settings that increase its size by so much?
> >
> > Warner
>
> Hello,
> I have a custom kernel with several drivers enabled, others disabled, but
> I'm not aware of any
> knowb I triggered by purpose that could change the size. Can you help me
> with some hints which
> knobs this might trigger? Since it happens on ALL boxes with CURRENT and
> different but similar
> custom kernel settings (mostly driver and disabling debugging et cetera it
> must be something
> very trivial that triggers that misbehaviour ... I doubt that kernel
> config is the cause, but
> anyway, I'll give you some extra configs I put on one box that fails:
>

The kernel.conf isn't used at all.

What do you have on /etc/src.conf, etc that's the only thing that will
control this.

Warner


> [... kernel conf ...]
>
> # The defaults are 64K and 128K respectively.
> options                 DFLTPHYS=(64*1024)
> #options                        MAXPHYS=(512*1024)
> options                 MAXPHYS=(1024*1024)
>
> options         CC_CDG
> options         CC_CHD
> options         CC_CUBIC
> options         CC_DCTCP
> options         CC_HD
> options         CC_HTCP
> options         CC_VEGAS
> options         RATELIMIT               # TX rate
>
> options                 ZFS                             # ZFS
> options         GEOM_NOP                # NOP GEOM class
> options                 GEOM_ELI
>
> options         LIBICONV                # kernels iconv
> options         LIBMCHAIN               # mchain library
> options         KGSSAPI                 # Kernel GSS API modulue
>
> options         MSDOSFS_ICONV   # MSDOS Filesystem
> options         CD9660_ICONV    # ISO 9660 Filesystem
>
> options         FDESCFS                 #File descriptor filesystem
> options         FUSEFS                  #FUSE support module
> options         AUTOFS                  # automounter filesystem
> options         NULLFS
>
> #options                P1003_1B_SEMAPHORES     # POSIX-style semaphores
> #options                P1003_1B_MQUEUE         # POSIX message queue
>
> options         TCPHPTS                                 # TCP High
> Precission timer
> #options                TCPPCAP                 # keeps the last n packets
> #options                MROUTING                # Multicast routing
> options                 IPSEC                   # Internet Protocol
> Security protocol
> #options                        TCP_SIGNATURE   # #include support for RFC
> 2385
> options                 SCTP            # Stream Control Transmission
> Protocol
>
> #
> options         MAC_BSDEXTENDED         # ugidfw
> options         MAC_PORTACL             #
> options         MAC_NTPD                #
> #
> options         CAM_IOSCHED_DYNAMIC             # CAM iosched NCQ TRIM
>
>
> --
> O. Hartmann
>