Re: [rfc] removing -mpreferred-stack-boundary=2 flag for i386?

On Sat, 24 Dec 2011, Alexander Best wrote:

> On Sat Dec 24 11, Bruce Evans wrote:
>> This almost builds in -current too.  I had to add the following:
>> - NO_MODULES to de-bloat the compile time
>> - MK_CTF=no to build -current on FreeBSD.9.  The kernel .mk files are
>>   still broken (depend on nonstandard/new features in sys.mk).
>
> strange. the build(7) man page claims that:
>
> "
>     WITH_CTF          If defined, the build process will run the DTrace CTF
>                       conversion tools on built objects.  Please note that
>                       this WITH_ option is handled differently than all other
>                       WITH_ options (there is no WITHOUT_CTF, or correspond-
>                       ing MK_CTF in the build system).
> "
>
> ... so setting MK_CTF to anything shouldn't have (according to the man page).

MK_CTF is an implementation detail.  It is normally set in bsd.own.mk
(not in sys.mk line I said -- this gives another, much larger bug (*)).
But when usr/share/mk is old, it doesn't know anything about MK_CTF.
(For example, in FreeBSD-9, sys.mk sets NO_CTF to 1 if WITH_CTF is not
defined.  This corresponds to bsd.own.mk in -current setting MK_CTF
to "no" if WITH_CTF is not defined.  Go back to an older version of
FreeBSD and /usr/share/mk/* won't know anything about any CTF variable.)
So when you try to build a current kernel under an old version of
FreeBSD, MK_CTF is used uninitialized and the build fails.  (Of course,
"you" build kernels normally and don't use the bloated buildkernel
method.)  The bug is in the following files:

     kern.post.mk:.if ${MK_CTF} != "no"
     kern.pre.mk:.if ${MK_CTF} != "no"
     kmod.mk:.if defined(MK_CTF) && ${MK_CTF} != "no"

except for the last one where it has been fixed.

(*) Well, not completely broken, but just annoyingly unportabile.
Consider the following makefile:

%%%
foo: foo.c
%%%

Invoking this under FreeBSD-9 gives:

%%%
cc -O2 -pipe   foo.c  -o foo
[ -z "ctfconvert" -o -n "1" ] ||  (echo ctfconvert -L VERSION foo &&  ctfconvert -L VERSION foo)
%%%

This is the old ctf method.  It is ugly but is fairly portable.

Invoking this under FreeBSD-9 but with -m<path-to-current-mk-directory> gives

%%%
cc -O2 -pipe   foo.c  -o foo
${CTFCONVERT_CMD} expands to empty string
%%%

This is because:
- the rule in sys.mk says ${CTFCONVERT_CMD}
- CTFCONVERT_CMD is normally defined in bsd.own.mk.  But bsd.own.mk is only
   included by BSD makefiles.  It is never included by portable makefiles.
   So ${CTFCONVERT_CMD} is used uninitialized.
- for some reason, using variables uninitialized is not fatal in this
   context, although it is for the comparisons of ${MK_CTF} above.
- ${CTFCONVERT_CMD} is replaced by the empty string.  Old versions of
   make warn about the use of an empty string as a shell command.
- the code that is supposed to prevent the previous warning is in
   bsd.own.mk, where it is not reached for portable makefiles.  It is:

% .if ${MK_CTF} != "no"
% CTFCONVERT_CMD=	${CTFCONVERT} ${CTFFLAGS} ${.TARGET}

This uses the full ctfconvert if WITH_CTF.

% .elif ${MAKE_VERSION} >= 5201111300
% CTFCONVERT_CMD=

make(1) has been modified to not complain about the empty string.  The
version test detects which versions of make don't complain.

% .else
% CTFCONVERT_CMD=	_at_:

The default is to generate this non-empty string and an extra shell command
to execute it, for old versions of make.

% .endif

But none of this works for portable makefiles, since it is not reached.

Bruce