L.S.

Was instructed (on irc.oftc.net:#gcc) to file a bug report. It seems gcc 
silently ignores __attribute__((aligned(N))) on stack variables (even 
with -mpreferred-stack-boundary=K, K >= 2logN). My own test is with:

compiler:

   Reading specs from /usr/lib/gcc-lib/i486-slackware-linux/3.2.3/specs
   Configured with: ../gcc-3.2.3/configure --prefix=/usr --enable-shared 

   --enable-threads=posix --enable-__cxa_atexit --disable-checking
   --with-gnu-ld --verbose --target=i486-slackware-linux
   --host=i486-slackware-linux
   Thread model: posix
   gcc version 3.2.3

commandline:

   gcc -W -Wall -o example example.c

or

   gcc -W -Wall -mpreferred-stack-boundary=12 -o example example.c

compiler output:

   none

program output (showing the alignment didn't work):

   read: Invalid argument

Works fine with the buffer in .bbs/.data. I can sort of imagine there 
might be good reasons for not allowing alignment on auto vars, but in 
that case, I guess a warning could be in order.

Also confirmed with current mainline on PPC by someone in the 
irc.oftc.net:#gcc

Preprocessed testcase attached. Testcase assumes linux kernel v2.6, on 
2.4 alignment for O_DIRECT needs to be to multiple of blocksize of 
underlying filesystem.

Hope this is useful.

Rene.