Re: EPICS base-3.15.9 fails to build with GCC-15

[Joel Sherrill via Tech-talk <tech-talk at aps.anl.gov>]

On Tue, Sep 29, 2026 at 4:38 PM Michael Davidsaver via Tech-talk <tech-talk at aps.anl.gov> wrote:

On 9/22/26 1:38 AM, Dmitry Yu. Bolkhovityanov via Tech-talk wrote:

Hi!

GCC-14 becomes mainstream (e.g. Debian-13), and familiar base-3.15.6 fails to build with it.  Fotrunately, 3.15.9 was built successfully, but I wanted to check it for "future-proofness" and tried building with GCC-15 and GCC-16.  It had failed with both.
...

GCC 14+ have been aggressive in trying to discourage use of error-prone language constructs, and the older standards which permitted them.  Some of the compile errors you mention should be avoidable by building with "make CMD_CFLAGS=-std=c89" (or C11 as Remi mentions).  I think not a long term solution, but with this older code maybe long enough?

It is too late to back fill this in properly but I think every project should pick a version of the language it is using and specify that in the build system. Not explicitly doing this leaves the language version to the whims of whatever gcc/llvm is installed. C11 wasn't a huge break with C99 and C17 is just a bug fix for C11. So there wasn't a huge breakage for years of C and compiler evolution. We were all just lucky. C23 has new features and keywords. GCC 15 defaults to C23. 

We were seeing this problem with RTEMS 5 on some packages. The newer distributions had newer compilers which defaulted to newer language versions. Chris Johns added support to the RTEMS Source Builder for us to add a standard way to specify the expected language version. This addressed the problem packages for RTEMS. 

I also am a lead on an avionics software standard that specifies specific language versions and off-limits features. It is not uncommon for people to not specify any -std or specify a version not allowed in the standard and then wonder why they don't pass conformance testing. It isn't a bad reflection on EPICS -std isn't specified. It unfortunately is not something that people seem to realize is important to define as a project requirement. "EPICS shall be written in Cnn or C++nn." 

I would also add that I pushed RTEMS to be warning free for "-Wall". Once warning free with that, we went to "-Wall -Werror" and then "-Wall -Wextra". Before all the -Wextra were fixed, I added -Wno-XXX to disable specific warnings. It is thankless work but is a worthy goal.

--joel
RTEMS