On Tue, 2012-10-30 at 11:58 -0500, Peter Bergner wrote: > I'm hitting the same bug as in PR53708 when compiling GLIBC's dlfcn.c when > vectorization is enabled on powerpc64-linux. A reduced test case is: > > bergner@bns:~/gcc/BUGS> cat foo.i > static void (*const init_array []) (void) > __attribute__ ((section (".init_array"), aligned (sizeof (void *)), used)) > = { 0 }; > > bergner@bns:~/gcc/BUGS> /home/bergner/gcc/build/gcc-fsf-4_7-base/gcc/xgcc > -B/home/bergner/gcc/build/gcc-fsf-4_7-base/gcc -S -m64 -O3 -maltivec foo.i -o > bad.s > > bergner@bns:~/gcc/BUGS> /home/bergner/gcc/build/gcc-fsf-4_7-pr53708/gcc/xgcc > -B/home/bergner/gcc/build/gcc-fsf-4_7-pr53708/gcc -S -m64 -O3 -maltivec foo.i > -o good.s > > bergner@bns:~/gcc/BUGS> diff -u bad.s good.s > --- bad.s 2012-10-30 10:41:15.000000000 -0500 > +++ good.s 2012-10-30 10:41:23.000000000 -0500 > @@ -2,7 +2,7 @@ > .section ".toc","aw" > .section ".text" > .section .init_array,"a" > - .align 4 > + .align 3 > .type init_array, @object > .size init_array, 8 > init_array: > > The above is bad, because the extra alignment causes the linker to add some > null padding to the init_array and the loader isn't expecting that and ends > up segv'ing. I'd like to backport Richard's patch below to the 4.7 branch. > The patch bootstrapped and regtested on powerpc64-linux with no regressions.
Commenting on Richard's question from the bugzilla: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53708#c10 I suppose if attribute((__aligned__)) truly does just set a minimum alignment value (and the documentation seems to say that) and the compiler is free to arbitrarily increase it, then the GLIBC code to scan the init_array needs to be tolerant of null values in init_array. Does everyone agree with that assessment? Peter