Make setting of CFLAGS_NOSTRICT make sense

Previously, we would set -fno-strict-aliasing only when
--enable-checking was given to configure but not
--enable-checking=all.  The intent seems to have been to
only warn about strict aliasing violations when --enable-checking=all
is in use, but that there was no need to disable the strict-aliasing
diagnostics when -Werror was not enabled.

Unfortunately, -fno-strict-aliasing affects not only the diagnostics
emitted by the compiler, but also the code generation!  So we were
leaving the normal (no --enable-checking) case with the compiler
assuming C's strict aliasing rules.  The OpenAFS codebase has
historically not been strict-aliasing safe (for example,
commit 15e8678661ec49f5eac3954defad84c06b3e0164 refers to a
runtime crash using a certain compiler version, which is diagnosed
as the compiler using the C strict aliasing rules to make
optimizations that exposed the invalid program code.

To avoid futher surprises due to new compiler optimizations
that utilize the C strict aliasing rules, always disable
strict aliasing except when --enable-checking=all is used.

Change-Id: Ib5d3bbd7c88686bd9a878b6b2c5e7c2b4eeccc04
Reviewed-on: https://gerrit.openafs.org/11988
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>

diff --git a/src/cf/osconf.m4 b/src/cf/osconf.m4
index becfac8..a13e3c1 100644 (file)
--- a/src/cf/osconf.m4
+++ b/src/cf/osconf.m4
@@ -633,7 +633,7 @@ else
 fi
 
 CFLAGS_NOERROR=
-CFLAGS_NOSTRICT=
+CFLAGS_NOSTRICT=-fno-strict-aliasing
 CFLAGS_NOUNUSED=
 CFLAGS_NOOLDSTYLE=
 XCFLAGS_NOCHECKING="$XCFLAGS"
@@ -646,10 +646,11 @@ if test "x$GCC" = "xyes"; then
     XCFLAGS="${XCFLAGS} -Wall -Wstrict-prototypes -Wold-style-definition -Werror -fdiagnostics-show-option -Wpointer-arith"
     if test "x$enable_checking" != "xall"; then
       CFLAGS_NOERROR="-Wno-error"
-      CFLAGS_NOSTRICT="-fno-strict-aliasing"
       CFLAGS_NOUNUSED="-Wno-unused"
       CFLAGS_NOOLDSTYLE="-Wno-old-style-definition"
       AC_DEFINE(IGNORE_SOME_GCC_WARNINGS, 1, [define to disable some gcc warnings in warnings-as-errors mode])
+    else
+      CFLAGS_NOSTRICT=
     fi
   fi
 else