Re: [dpdk-dev] [PATCH] mk: toolchain: gcc: query the compiler macros to obtain the gcc version

[Thomas Monjalon <thomas.monjalon@6wind.com>]

2016-03-22 22:50, Markos Chandras:
> On 22/03/16 22:34, Thomas Monjalon wrote:
> > 2016-03-22 17:13, Markos Chandras:
> >> This is similar to what's being used in the Linux kernel. Querying the
> >> GCC macros directly gives more accurate results compared to -dumpversion
> >> which could vary across distributions.
> >>
> >> Signed-off-by: Markos Chandras <mchandras@suse.de>
> >> ---
> >> In openSUSE Tumbleweed (and in any other SUSE distribution which
> >> uses (or will use) gcc >= 5), gcc -dumpversion returns '5'. This is on
> >> purpose as discussed in https://bugzilla.opensuse.org/show_bug.cgi?id=941428
> > 
> > Good to know. It could be in the commit log.
> 
> I can add this information to the commit message and send a v2 if needed.

I will apply with this info.

> >> -GCC_VERSION = $(subst .,,$(shell $(CC) -dumpversion | cut -f1-2 -d.))
> >> +GCC_MAJOR = $(shell echo __GNUC__ | $(CC) -E -x c - | tail -n 1)
> >> +GCC_MINOR = $(shell echo __GNUC_MINOR__ | $(CC) -E -x c - | tail -n 1)
> >> +GCC_VERSION = $(GCC_MAJOR)$(GCC_MINOR)
> > 
> > Are we sure the minor will always be only one digit?
> 
> Well, I can't be sure but minor has always been a single digit since gcc
> >= 3 if I am not mistaken. But does it matter? What if it is two or more
> digits? The previous code did something similar so if you had gcc
> 5.12.34 installed (and lets assume this is what is being returned by
> -dumpversion), it would have returned 512. The comparison would still
> work as it is at the moment no?

Yes, I was asking for an improvement in case it could happen.
But GCC is probably conservative with numbering so we can keep only one digit.