[libc] Allow build_assert() failures to be ignored via NO_WERROR=1

We build with -Werror by default so that any warning is treated as an
error and aborts the build.  The build system allows NO_WERROR=1 to be
used to override this behaviour, in order to allow builds to succeed
when spurious warnings occur (e.g. when using a newer compiler that
includes checks for which the codebase is not yet prepared).

Some versions of gcc (observed with gcc 4.8.5 in CentOS 7) will report
spurious build_assert() failures: the compilation will fail due to an
allegedly unelided call to the build assertion's external function
declared with __attribute__((error)) even though the compiler does
manage to successfully elide the call (as verified by the fact that
there are no unresolvable symbol references in the compiler output).

Change build_assert() to declare __attribute__((warning)) instead of
__attribute__((error)) on its extern function.  This will still abort
a normal build if the assertion fails, but may be overridden using
NO_WERROR=1 if necessary to work around a spurious assertion failure.

Note that if the build assertion has genuinely failed (i.e. if the
compiler has genuinely not been able to elide the call) then the
object will still contain an unresolvable symbol reference that will
cause the link to fail (which matches the behaviour of the old
linker_assert() mechanism).

Signed-off-by: Michael Brown <mcb30@ipxe.org>

0 files changed, 0 insertions, 0 deletions