arch/i386/Makefile,scripts/gcc-version.sh,Makefile small fixes

[This patch is against 2.6.2-rc1-mm2]

arch/i386/Makefile:
* omitted $(KBUILD_SRC)/ in script call.

scripts/gcc-version.sh:
* GNU tail no longer supports 'tail -1' syntax.

Makefile:
* There is no point in adding -funit-at-a-time option because it is enabled by default at levels -Os, -O2 and -O3.

* Consider adding -fweb option:

vanilla:

   $ size vmlinux
      text    data     bss     dec     hex filename
   3056270  526780  386056 3969106  3c9052 vmlinux

with -fweb:

   $ size vmlinux
      text    data     bss     dec     hex filename
   3049523  526780  386056 3962359  3c75f7 vmlinux

Also note 0.1 ... 1.0% speedup in various benchmarks. This option is not enabled by default at -O2 because it (like -fomit-frame-pointer) makes debugging impossible.

diff -urN vanilla-2.6.2-rc1-mm2/arch/i386/Makefile hack/arch/i386/Makefile
@@ -70,7 +70,7 @@
 
 # -mregparm=3 works ok on gcc-3.0 and later
 #
-GCC_VERSION			:= $(shell $(CONFIG_SHELL) scripts/gcc-version.sh $(CC))
+GCC_VERSION			:= $(shell $(CONFIG_SHELL) $(KBUILD_SRC)/scripts/gcc-version.sh $(CC))
 cflags-$(CONFIG_REGPARM) 	+= $(shell if [ $(GCC_VERSION) -ge 0300 ] ; then echo "-mregparm=3"; fi ;)
 
 CFLAGS += $(cflags-y)

diff -urN vanilla-2.6.2-rc1-mm2/scripts/gcc-version.sh hack/scripts/gcc-version.sh
@@ -8,7 +8,7 @@
 
 compiler="$*"
 
-MAJOR=$(echo __GNUC__ | $compiler -E -xc - | tail -1)
-MINOR=$(echo __GNUC_MINOR__ | $compiler -E -xc - | tail -1)
+MAJOR=$(echo __GNUC__ | $compiler -E -xc - | tail -n 1)
+MINOR=$(echo __GNUC_MINOR__ | $compiler -E -xc - | tail -n 1)
 printf "%02d%02d\\n" $MAJOR $MINOR
 

diff -urN vanilla-2.6.2-rc1-mm2/Makefile hack/Makefile
@@ -435,15 +435,12 @@
 
 ifndef CONFIG_FRAME_POINTER
 CFLAGS		+= -fomit-frame-pointer
+CFLAGS		+= $(call check_gcc,-fweb,)
 endif
 
 ifdef CONFIG_DEBUG_INFO
 CFLAGS		+= -g
 endif
-
-# Enable unit-at-a-time mode when possible. It shrinks the
-# kernel considerably.
-CFLAGS += $(call check_gcc,-funit-at-a-time,)
 
 # warn about C99 declaration after statement
 CFLAGS += $(call check_gcc,-Wdeclaration-after-statement,)

Is appreciated, thanks.

OK

OK.

hm. Didn't Andi say that adding -fno-unit-at-a-time caused code shrinkage?

What does it do?

OK, then we'd need a config option for it.

Also, at least for the Fedora gcc-ssa compiler, -funit-at-a-time is *not* a default option (provably so - building with gcc-ssa makes a kernel that hangs *very* early on (right after 'decompressing the kernel' - I haven't dug into this yet) - but commenting out this:

# Enable unit-at-a-time mode when possible. It shrinks the

# kernel considerably.
CFLAGS += $(call check_gcc,-funit-at-a-time,)

results in a working kernel. This is with:

% gcc-ssa --version
gcc-ssa (GCC) 3.5-tree-ssa 20040115 (Fedora Core Rawhide 3.5ssa-108)

But for gcc-3_4-branch (3.4.0 prerelease) and mainline (3.5.0 experimental) -funit-at-a-time is default (at -O2 and higher) and works (at least for me :-).

-fweb
Constructs webs as commonly used for register allocation purposes and assign each web individual pseudo register. This allows our register allocation pass to operate on pseudos directly, but also strengthens several other optimization passes, such as CSE, loop optimizer and trivial dead code remover. It can, however, make debugging impossible, since variables will no longer stay in a ``home register''.

Enabled at levels -O3.