Date: Fri, 7 Dec 2001 07:56:30 +1100 (EST) From: Bruce Evans <bde@zeta.org.au> To: "David E. O'Brien" <obrien@FreeBSD.org> Cc: <cvs-committers@FreeBSD.org>, <cvs-all@FreeBSD.org> Subject: Re: cvs commit: src/sys/conf kern.pre.mk Message-ID: <20011207072556.E16470-100000@gamplex.bde.org> In-Reply-To: <200112061753.fB6HrWa49164@freefall.freebsd.org>
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On Thu, 6 Dec 2001, David E. O'Brien wrote:
> obrien 2001/12/06 09:53:32 PST
>
> Modified files:
> sys/conf kern.pre.mk
> Log:
> Compile all kernels with "-ffreestanding":
>
> Assert that compilation takes place in a freestanding environment. This
> implies `-fno-builtin'. A freestanding environment is one in which the
> standard library may not exist, and program startup may not necessarily be
> at main. The most obvious example is an OS kernel. This is equivalent to
> `-fno-hosted'.
Builtins are required for some optimizations. Some relevant history:
! davidg 95/05/01 22:20:30
!
! Modified: sys/i386/i386 support.s
! Log:
! Added a memcpy() routine.
!
!
! davidg 95/05/01 22:35:08
!
! Modified: sys/sys systm.h
! Log:
! Added prototype for memcpy(). Changed size argument of "b" functions to
! size_t.
!
!
! davidg 95/05/09 06:35:49
!
! Modified: sys/net bpf.c if_ethersubr.c if_fddisubr.c
! sys/netinet if_ether.c ip_input.c ip_output.c tcp_output.c
! udp_usrreq.c
! Log:
! Replaced some bcopy()'s with memcpy()'s so that gcc while inline/optimize.
!
!
! bde 96/06/08 01:19:10
!
! Modified: sys/i386/isa random_machdep.c
! Log:
! Replaced some memcpy()'s by bcopy()'s.
!
! gcc only inlines memcpy()'s whose count is constant and didn't inline
! these. I want memcpy() in the kernel go away so that it's obvious that
! it doesn't need to be optimized. Now it is only used for one struct
! copy in si.c.
!
! Revision Changes Path
! 1.7 +3 -3 src/sys/i386/isa/random_machdep.c
!
! Modified: sys/net bpf.c
! sys/netinet if_ether.c ip_input.c ip_output.c tcp_output.c
! udp_usrreq.c
! Log:
! Changed some memcpy()'s back to bcopy()'s.
!
! gcc only inlines memcpy()'s whose count is constant and didn't inline
! these. I want memcpy() in the kernel go away so that it's obvious that
! it doesn't need to be optimized. Now it is only used for one struct
! copy in si.c.
!
! Revision Changes Path
! 1.26 +2 -2 src/sys/net/bpf.c
! 1.30 +2 -2 src/sys/netinet/if_ether.c
! 1.43 +2 -2 src/sys/netinet/ip_input.c
! 1.40 +5 -5 src/sys/netinet/ip_output.c
! 1.21 +2 -2 src/sys/netinet/tcp_output.c
! 1.28 +2 -2 src/sys/netinet/udp_usrreq.c
!
!
! peter 96/06/17 11:52:57
!
! Modified: sys/i386/isa si.c
! Log:
! This time, get rid of the struct copies that were really causing gcc to
! call memcpy.. It seems that gcc would not inline the implicit call
! when copying from a volatile...
!
! Revision Changes Path
! 1.45 +4 -4 src/sys/i386/isa/si.c
!
!
! bde 96/07/12 00:18:14
!
! Modified: sys/i386/i386 pmap.c
! Log:
! Removed "optimization" using gcc's builtin memcpy instead of bcopy.
! There is little difference now since the amount copied is large,
! and bcopy will become much faster on some machines.
!
! Revision Changes Path
! 1.109 +2 -5 src/sys/i386/i386/pmap.c
I never completed removing memcpy() like I said I wanted in my 96/06/08
commit (see above). The is many times larger now. The slightly pessimal
extern memcpy is now referred to in about 70 .o's in LINT.
Kernel Makefiles should set -fbuiltin together with -ffreestanding
until these optimizations are reorganized. memcpy() should be an
inline function (actually named bcopy()) that calls __bultin_memcpy()
when appropriate.
I think -ffreestanding and -fbuiltin should be set in bsd.kern.mk so
that they get used for modules.
BTW, kern.{post,pre}.mk complicate debugging of kernel Makefiles. I'd
like config(8) to merge in all include files at config time.
Bruce
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