Re: [Oorexx-devel] Changing compile warning options on unix.

[Mike C. <MF...@uk...>]

> I wanted to try specifying the -Wstrict-alias option on the=20
> compiles per Mike Cowlishaw's suggestion, but I'm not sure this
> is working.  I found the warnings section in the configure.ac=20
> file and added those options there, be I don't see any evidence
> that they're getting used.  The g++ command lines used by the=20
> build are not showing any -W options on the line.  Is there=20
> something not setup properly with the autoconfig?=20

It might be one of several things:=20

 -- GCC too old (I found that 3.4.3 accepted the setting but gave no=20
warnings)
=20
 -- cases being missed by GCC (I typically only got a few warnings, even=20
in a source file with dozens of cases where I expected a warning, and=20
places where optimization in XLC broke the code)

 -- might need to enable the optimization, too; I always have=20
-fstrict-aliasing set.

 -- no 'bad' cases in the code.

Here's a wee program that should generate the message:

 #include <stdio.h>
 int main(int argc, char *argv[]) {
  int    u=3D0x00010002;
  short *s;
  if (argc>0) printf("%s starting...\n",  argv[0]); /* quiet compiler */
  s=3D(short *)&u;
  printf(" s=3D[%d, %d]\n", (int)s[0], (int)s[1]);
  return 0;
  } /* main */

And here's what I get during compile and run (showing the actuall GCC=20
options used [and other historical detritus]):

 Building strict GCC C99 [cleanObj]...
 Compile  [strict.c]...
    425 *-* comp compout||ofile sfile errdo
        >>>   "gcc -c  -DOSLINUX=3D1   -DLINUX=3D1 -O3 -march=3Di686 -DGCC =
-Wall=20
-W -Wwrite-strings -Wstrict-prototypes  -Wmissing-prototypes -Wcast-align=20
-Waggregate-return -Wnested-externs -fstrict-aliasing -Wstrict-aliasing=20
-pthread -D=5FREENTRANT -std=3Dc99 -pedantic -o strict.o strict.c 2>=20
strict.err"
    430 *-*     typecmd errfile
        >>>       "cat strict.err"
 strict.c: In function ?main?:
 strict.c:10: warning: dereferencing type-punned pointer will break=20
strict-aliasing rules
 Link     [strict.o]...
    490 *-*   link||ofile links linklibs linkopts errdo
        >>>     "gcc -o strict.exe strict.o  -lrt -ldl -lpthread -mwindows =

-mconsole 2> link.err"
=20
 ./strict.exe starting...
  s=3D[2, 1]

Mike

[For more info: =20
http://www.cellperformance.com/mike=5Facton/2006/06/understanding=5Fstrict=
=5Faliasing.html=20
]







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