Le mercredi 31 mars 2010 à 14:00 -0700, David Miller a écrit :

Funny how going back in time gives us better diagnostic messages from
the compiler :-)

FWIW I also didn't get the warning, and that was with gcc-4.5 built
from the gcc trunk just the other day.

I suspect this is to do with a change to what warnings get enabled by
default with the -W options we put in the cflags rather than gcc
losing the ability to detect this case.

  x86_64-unknown-linux-gcc -Wp,-MD,drivers/net/bonding/.bond_main.o.d
-nostdinc
-isystem /data/x86-64/lib/gcc/x86_64-unknown-linux/4.1.2/include
-I/data/src/linux-2.6/arch/x86/include -Iinclude  -include
include/generated/autoconf.h -D__KERNEL__ -Wall -Wundef
-Wstrict-prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common
-Werror-implicit-function-declaration -Wno-format-security
-fno-delete-null-pointer-checks -O2 -m64 -mno-red-zone -mcmodel=kernel
-funit-at-a-time -maccumulate-outgoing-args -DCONFIG_AS_CFI=1
-DCONFIG_AS_CFI_SIGNAL_FRAME=1 -pipe -Wno-sign-compare
-fno-asynchronous-unwind-tables -mno-sse -mno-mmx -mno-sse2 -mno-3dnow
-fno-stack-protector -fno-omit-frame-pointer -fno-optimize-sibling-calls
-g -pg -Wdeclaration-after-statement -Wno-pointer-sign
-D"KBUILD_STR(s)=#s" -D"KBUILD_BASENAME=KBUILD_STR(bond_main)"
-D"KBUILD_MODNAME=KBUILD_STR(bonding)"  -c -o
drivers/net/bonding/.tmp_bond_main.o drivers/net/bonding/bond_main.c
drivers/net/bonding/bond_main.c: In function ‘bond_xmit_roundrobin’:
drivers/net/bonding/bond_main.c:4159: warning: comparison is always
false due to limited range of data type


while with gcc-4.4.2 (native compiler, no warning displayed)

 gcc -Wp,-MD,drivers/net/bonding/.bond_main.o.d  -nostdinc
-isystem /usr/lib/gcc/x86_64-linux-gnu/4.4.3/include
-I/usr/src/git/linux-2.6/arch/x86/include -Iinclude  -include
include/generated/autoconf.h -D__KERNEL__ -Wall -Wundef
-Wstrict-prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common
-Werror-implicit-function-declaration -Wno-format-security
-fno-delete-null-pointer-checks -O2 -m64 -mtune=generic -mno-red-zone
-mcmodel=kernel -funit-at-a-time -maccumulate-outgoing-args
-DCONFIG_AS_CFI=1 -DCONFIG_AS_CFI_SIGNAL_FRAME=1 -pipe -Wno-sign-compare
-fno-asynchronous-unwind-tables -mno-sse -mno-mmx -mno-sse2 -mno-3dnow
-Wframe-larger-than=1024 -fno-stack-protector -fno-omit-frame-pointer
-fno-optimize-sibling-calls -g -Wdeclaration-after-statement
-Wno-pointer-sign -fno-strict-overflow -fno-dwarf2-cfi-asm
-fconserve-stack   -D"KBUILD_STR(s)=#s"
-D"KBUILD_BASENAME=KBUILD_STR(bond_main)"
-D"KBUILD_MODNAME=KBUILD_STR(bond_main)"  -c -o
drivers/net/bonding/.tmp_bond_main.o drivers/net/bonding/bond_main.c


New compiler got these new options :  -Wframe-larger-than=1024
-fno-strict-overflow -fno-dwarf2-cfi-asm -fconserve-stack