[LTP] Fixing cleanup function with weak references [was Re: Build breakage caused by changes in regen.sh]

[Garrett C. <yan...@gm...>]

On Thu, Nov 26, 2009 at 2:05 PM, Garrett Cooper <yan...@gm...> wrote:
>    It seems that the gcc / binutils WAS optimizing out a code branch
> w.r.t. the syscall macro. I'm aware of the problem and trudging
> through slowly working out compile time issues. I'll try to get it
> done sometime tonight...

Ok, I have a solution for these issues, but I want to make sure that
what I'm doing is correct:

gcooper@orangebox /scratch/ltp-dev2/ltp $ cdiff
testcases/kernel/include/regen.sh
Index: testcases/kernel/include/regen.sh
===================================================================
RCS file: /cvsroot/ltp/ltp/testcases/kernel/include/regen.sh,v
retrieving revision 1.14
diff -u -r1.14 regen.sh
--- testcases/kernel/include/regen.sh   26 Nov 2009 22:08:52 -0000      1.14
+++ testcases/kernel/include/regen.sh   27 Nov 2009 06:46:46 -0000
@@ -29,7 +29,9 @@
  * result in compile-time errors and folks get the granularity they desire
  * when writing testcases.
  */
-void cleanup(void) __attribute__ ((weak));
+static void syscall_cleanup_stub(void) __attribute__ ((weakref ("cleanup")));
+
+static void cleanup(void);

 #define syscall(NR, ...) ({ \\
        int __ret; \\
@@ -40,7 +42,8 @@
                __ret = syscall(NR, ##__VA_ARGS__); \\
        } \\
        if (__ret == -1 && errno == ENOSYS) { \\
-               tst_brkm(TCONF, cleanup, "syscall " #NR " not
supported on your arch"); \\
+               tst_brkm(TCONF, syscall_cleanup_stub, \\
+                       "syscall " #NR " not supported on your arch"); \\
                errno = ENOSYS; \\
        } \\
        __ret; \\

    This creates a weak reference to cleanup (which is undefined by
default) and if someone specifies cleanup in a file that includes this
header, it'll overwrite that with the strong reference, by design.
    Now, I used syscall_cleanup_stub for 1) readability, 2) to ensure
that I didn't have to change a bunch of files that #include
linux_syscall_numbers.h that define cleanup.
    I've tested it out in the following cases and it verified that it
works as expected:
    1. cleanup defined (strong reference) - put a printout in the
strong reference copy of the cleanup function.
    2. cleanup undefined (weak reference only).
    Is there any potential coverage I'm missing? Should this be
defined somewhere else or be defined differently? My only concern is
that this restricts the header to gcc-compatible compiler only
compilation (icc included), as not all compilers have the
__attribute__ qualifier.
    On the plus side, this gets past the previously mentioned build
breakage and also mutes a lot of compiler warnings related to cleanup
being unused / unreferenced, as it was previously just a function
prototype in the header file.
Thanks!
-Garrett