FWIW this simple .export OBJTOP works ok for buildworld but not for targets like universe where multiple arches try to use the same OBJTOP which quickly ends in tears.
The more elaborate patch in https://reviews.freebsd.org/D54819 blows up in buildworld due to being incompatible with assumptions made by all the *compat* bits, but once that compat stuff is fixed, probably has a hope of working for universe too.

In D54819#1253097, @jrtc27 wrote:

Do we need to worry about $s in OBJROOT?

Remove all but the last := for OBJTOP

Please see https://reviews.freebsd.org/D54819

The patch below, builds buildworld ok, avoids these warnings (due to OBJTOP being empty when evaluatinng MAKEOBJDIR which is set to ${.CURDIR:S,${SRCTOP},${OBJTOP},}

diff --git a/share/mk/src.sys.obj.mk b/share/mk/src.sys.obj.mk
index e4fe3fa9a2aa..67af0b833faa 100644
--- a/share/mk/src.sys.obj.mk
+++ b/share/mk/src.sys.obj.mk
@@ -88,18 +88,22 @@ SB_OBJROOT:= ${OBJROOT}
 # in the source tree.
 .if ${MK_UNIFIED_OBJDIR} == "yes" && ${SRCTOP} != ${OBJROOT:tA}
 .if defined(TARGET) && defined(TARGET_ARCH)
-OBJTOP:=       ${OBJROOT}${TARGET}.${TARGET_ARCH}
+OBJTOP:=       ${OBJROOT}$${TARGET}.$${TARGET_ARCH}
 .elif defined(TARGET) && ${.CURDIR} == ${SRCTOP}
 # Not enough information, just use basic OBJDIR.  This can happen with some
 # 'make universe' targets or if TARGET is not being used as expected.
 OBJTOP:=       ${OBJROOT:H}
 .else
-OBJTOP:=       ${OBJROOT}${MACHINE}.${MACHINE_ARCH}
+OBJTOP:=       ${OBJROOT}$${MACHINE}.$${MACHINE_ARCH}
 .endif
 .else
 # TARGET.TARGET_ARCH handled in OBJROOT already.
 OBJTOP:=       ${OBJROOT:H}
 .endif # ${MK_UNIFIED_OBJDIR} == "yes"
+# export but do not track
+.export-env OBJTOP
+# resolve if needed
+OBJTOP:= ${OBJTOP}
 .endif # empty(OBJTOP)

Fix CVS Ids

Looks fine

In D53429#1221417, @jhb wrote:

Eh, I'm not sure this is actually the style we want? Lots of places in the tree fix the diff problem by just using multiple += statements, e.g.:

FOO= foo
FOO+= bar
FOO+= baz

Perfect, thank you. Should I wait for this to find it's way to FreeBSD or apply the change locally?

No need for a comment, I committed the following upstream:

Index: var.c
===================================================================
RCS file: /cvsroot/src/usr.bin/make/var.c,v
retrieving revision 1.1171
diff -u -p -r1.1171 var.c
--- var.c       29 Jun 2025 11:02:17 -0000      1.1171
+++ var.c       16 Sep 2025 15:13:28 -0000
@@ -1850,7 +1850,7 @@ QuoteShell(const char *str, bool quoteDo
 static char *
 Hash(const char *str)
 {
-       static const char hexdigits[16] = "0123456789abcdef";
+       static const char hexdigits[] = "0123456789abcdef";
        const unsigned char *ustr = (const unsigned char *)str;

In case it isn't obvious, we can't stub or #ifdef this in libsa since that is presumably shared by all loaders for a given arch, thus a non-optional src from loader.mk would seem to make sense - misc.c seemed as good as any?

Good move

Split out fs_ops.fs_flag to D51684

In D51443#1179395, @jrtc27 wrote:

To make this work in cheribuild I passed INSTALL="sh /path/to/src/tools/install.sh". Doing something automatically here that works would be good, though I'd want confirmation from someone like @sjg that ${.OBJDIR}/.. is definitely going to always be world's ${OBJTOP}.

works for me, just one nit above

Note I would disagree that make isn't needed in a minimal install, I use make and makefiles for all sorts of use-cases that have nothing to do with building src/

Looks reasonable

In D51447#1175667, @imp wrote:

I do like this better...

But what we're trying to avoid is setting currdir to tftp://1.2.3.4/mumble and having lots of tftp traffic go as we try to open it a bunch of times to see if each of the filesystems can cope... Can you confirm that's the top of this rabbit hole?

Rework to avoid opening dirs via TFTP while not breaking diskless
boot with nfs.

I can't approved, but looks sane - I assume it works ;-)

Move install.c change to D51446
Move misc.c change to D51447

Mention pkgfs_fsops in libsa.3

Add flag to fs_ops for skipping devopen

This review has been broken up and the open review is D51187

Make the code in open() neater

Alternative means of skipping devopen for pkgfs

Rebase after commit DEBUG_PRINTF

In D51269#1173596, @imp wrote:

This looks good.

It would be nice if there was a loader command to set the debug level, but that's a separate thing and isn't universally useful since a lot of this code runs before the OK prompt.

In D51094#1172979, @imp wrote:

I had a note to follow up on this in a "little while"
Where are we? Is this review done? Or have I overlooked some sub-review that split off?

Tweak the #ifdef in stand.h

In D51187#1170063, @imp wrote:

Can you do the debug level stuff first so we get that out of the way? There's also a lot of different fixes bundled together which makes me super nervous for future bisecting...