Compiling with gcc 15 and UNREACHABLE_CODE, NORETURN errors

[andreasbaumann]

Seems newer compilers can actually reach UNREACHABLE_CODE and complain about
it not being defined anywhere (on Archlinux, gcc 15.2.1):

util/LLgen/src/gencode.c: In function ‘prset’:
util/LLgen/src/gencode.c:463:9: error: ‘UNREACHABLE_CODE’ undeclared (first use in this function)
  463 |         UNREACHABLE_CODE;
      |         ^~~~~~~~~~~~~~~~
util/LLgen/src/gencode.c:463:9: note: each undeclared identifier is reported only once for each function it appears in
[27/9927] HOSTCC util/LLgen/+LLgen/util/LLgen/src/LLgen.c

Also there are warnings about NORETURN:

    In file included from modules/src/data/warnings.c:4:
.obj/modules/src/data/+data_hdr/warnings.h:7:16: error: expected ‘;’ before ‘void’
    7 | extern NORETURN void fatal(const char* fmt, ...);
      |                ^~~~~
      |                ;

I was able to build it with minimal (actually no) code changes by setting::

make CFLAGS='-DUNREACHABLE_CODE="__builtin_unreachable()" -DNORETURN="__attribute__((noreturn))"'

Not sure, if this needs any real fix inside the code itself. Maybe it's enough that other
people see a workaround in this bug when building with newer compilers?

[davidgiven]

You don't have CFLAGS defined in the environment, do you? If so, that'll be overriding the definition in the Makefile. I should change it so that the two necessary defines are always added to CFLAGS.

[andreasbaumann]

I'm explicitely overwriting them (because of something else):

https://aur.archlinux.org/cgit/aur.git/tree/PKGBUILD?h=ack-git#n29

[davidgiven]

After some fiddling, the magic in the Makefile is:

CFLAGS ?= -g -Os \
        -Werror=return-type \
        -Werror=implicit-function-declaration \
        -Werror=strict-prototypes

override CFLAGS += \
        -DUNREACHABLE_CODE='__builtin_unreachable()' \
        -DNORETURN=_Noreturn

But really the two special definitions should be added in the build.py. I'll fix that.

[andreasbaumann]

Ok, thanks. :-)