conflicting switches: -march=armv7-a -mcpu=cortex-a8

[Jussi Hakala]

Is combination of -march=armv7-a -mcpu=cortex-a8 or is this an issue with the compiler? Trying mtune instead of mcpu seems to work okay. Didn't find anything related to this from gcc's 4.5 release pages.

$ echo | arm-linux-gnueabi-gcc -march=armv7-a -mcpu=cortex-a8 -xc -
<stdin>:1:0: warning: switch -mcpu=cortex-a8 conflicts with -march= switch
/usr/lib/gcc/arm-linux-gnueabi/4.5.1/../../../../arm-linux-gnueabi/lib/crt1.o: In function `_start':
(.text+0x34): undefined reference to `main'
collect2: ld returned 1 exit status

$ arm-linux-gnueabi-gcc --version
arm-linux-gnueabi-gcc (Ubuntu/Linaro 4.5.1-7ubuntu1) 4.5.1
Copyright (C) 2010 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ cat /etc/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=10.10
DISTRIB_CODENAME=maverick
DISTRIB_DESCRIPTION="Ubuntu 10.10"

[Julian Brown (julian-codesourcery)]

Specifying both -march= and -mcpu= is redundant, and may not in fact have done what you expected in previous compiler versions (maybe even depending on the order in which the arguments were given). The -march switch selects a "generic" ARMv7-A CPU, and -mcpu selects specifically a Cortex-A8 CPU with tuning specific for that core.

Either use "-march=armv7-a -mtune=cortex-a8", or just use "-mcpu=cortex-a8".

[Julian Brown (julian-codesourcery)]

OTOH, http://gcc.gnu.org/ml/gcc-patches/2010-06/msg00229.html may be related.

[Jussi Hakala (jussi-hakala)]

The gcc man page suggests that -march can be used "in conjunction with or instead of the -mcpu= option".

And quoting the behavior in the patch, when both -march and -mcpu is set, given the consistency, they are treated equal with only -mcpu set, which makes sense. However that particular patch doesn't seem to be applied in Linaro-4.5-2010.10-0.

Currently switched to -mtune instead of -mcpu, but still feeling a bit confused.

[Michael Hope (michaelh1)]

Fixed in Linaro GCC 2010.11.