Re: stdalign test with HP-UX cc

[Paul Eggert]

Bruno Haible wrote:

> Emacs 25.1 cannot be built with this compiler.

Thanks for looking into this. Ouch. It looks like HP-UX cc has serious bugs in 
its implementation of C99 flexible array members. I added this issue to 
emacs/etc/PROBLEMS, and am suggesting GCC instead of HP-UX cc for people who 
want to build Emacs on HP-UX. See:

http://git.savannah.gnu.org/cgit/emacs.git/commit/?id=a09473261c8b11243e68d84c5dc2448d65a67e77


>   CCLD     ebrowse
> cc: "ebrowse.c", line 281: error 1687: Illegal use of flexible array: structs 
> with FAMs cannot be members of other structs.

This suggests that the HP-UX cc flexible array member bug is as follows: if a 
struct X contains a 'struct Y *' member where 'struct Y' has a flexible array 
member, the compiler incorrectly rejects the definition of struct X. Does the 
attached Gnulib patch suffice to detect the HP-UX cc bug? If so, this should fix 
Emacs's problem with flexible array members on HP-UX cc. I installed this patch 
into Gnulib since it shouldn't hurt even if it doesn't catch the HP-UX cc bug.


For the problem with __attribute__ ((__aligned__ (8))), does it suffice to put 
the declaration after the identifier? E.g., does this compile:

int foo __attribute__ ((__aligned__ (8))) = 10;

whereas this does not compile?

int __attribute__ ((__aligned__ (8))) bar = 20;

If so, I think we can work around this problem in Emacs (even if we cannot solve 
the problem in general for Gnulib stdalign), and something like the patch you 
proposed should suffice for Gnulib (although we'd also need to fix 
m4/stdalign.m4 to keep it in sync with lib/stdalign.in.h).

Also, in your build of Emacs 25.1, is the symbol HAVE_STRUCT_ATTRIBUTE_ALIGNED 
defined in src/config.h?

0001-flexmember-try-to-detect-HP-UX-11.31-cc-bug.patch
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