Re: stdalign test with HP-UX cc

[Bruno Haible]

Hi Paul,

> >   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.

Confirmed:
$ cat foo.c
struct Y {
  int a;
  char b[];
};

struct X {
  int b;
  struct Y *p;
};

$ cc -AC99 -c foo.c
cc: "foo.c", line 6: error 1687: Illegal use of flexible array: structs with 
FAMs cannot be members of other structs. 

> Does the 
> attached Gnulib patch suffice to detect the HP-UX cc bug?

Yes. Output before your patch:
checking for flexible array member... yes
and after your patch:
checking for flexible array member... no

> 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;

No, nothing like this works.

$ cat foo.c
int aa __attribute__ ((__aligned__ (8))) = 10;

int ab __attribute__ ((aligned (8))) = 10;

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

int __attribute__ ((aligned (8))) ad = 10;

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

__attribute__ ((aligned (8))) int af = 10;

$ cc -AC99 -c foo.c
cc: "foo.c", line 1: error 1000: Unexpected symbol: "8".
cc: "foo.c", line 1: error 1670: Illegal attribute __aligned__ specified.
cc: "foo.c", line 3: error 1000: Unexpected symbol: "8".
cc: "foo.c", line 3: error 1670: Illegal attribute aligned specified.
cc: "foo.c", line 5: error 1000: Unexpected symbol: "8".
cc: "foo.c", line 5: error 1670: Illegal attribute __aligned__ specified.
cc: "foo.c", line 7: error 1000: Unexpected symbol: "8".
cc: "foo.c", line 7: error 1670: Illegal attribute aligned specified.
cc: "foo.c", line 9: error 1000: Unexpected symbol: "8".
cc: "foo.c", line 9: error 1670: Illegal attribute __aligned__ specified.
cc: "foo.c", line 11: error 1000: Unexpected symbol: "8".
cc: "foo.c", line 11: error 1670: Illegal attribute aligned specified.

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

No, it's #undef'ed.

> (although we'd also need to fix m4/stdalign.m4 to keep it in sync with
> lib/stdalign.in.h).

Good point. Here's a revised proposed patch.


2017-03-17  Bruno Haible  <address@hidden>

        stdalign: Make it work with HP-UX cc.
        * lib/stdalign.in.h (_Alignas): Don't define for HP-UX cc.
        * m4/stdalign.m4 (gl_STDALIGN_H): No need to enable the extra test
        for HP-UX cc.

diff --git a/lib/stdalign.in.h b/lib/stdalign.in.h
index c2b791e..f6f4190 100644
--- a/lib/stdalign.in.h
+++ b/lib/stdalign.in.h
@@ -103,7 +103,7 @@
 # elif ((defined __APPLE__ && defined __MACH__                  \
          ? 4 < __GNUC__ + (1 <= __GNUC_MINOR__)                 \
          : __GNUC__)                                            \
-        || 061200 <= __HP_cc || 061200 <= __HP_aCC                \
+        || 061200 <= __HP_aCC                                   \
         || __ICC || 0x590 <= __SUNPRO_C || 0x0600 <= __xlC__)
 #  define _Alignas(a) __attribute__ ((__aligned__ (a)))
 # elif 1300 <= _MSC_VER
diff --git a/m4/stdalign.m4 b/m4/stdalign.m4
index 3a12658..5c15ef0 100644
--- a/m4/stdalign.m4
+++ b/m4/stdalign.m4
@@ -35,7 +35,7 @@ AC_DEFUN([gl_STDALIGN_H],
                  || (defined __APPLE__ && defined __MACH__ \
                      ? 4 < __GNUC__ + (1 <= __GNUC_MINOR__) \
                      : __GNUC__) \
-                 || __HP_cc || __HP_aCC || __IBMC__ || __IBMCPP__ \
+                 || __HP_aCC || __IBMC__ || __IBMCPP__ \
                  || __ICC || 0x5110 <= __SUNPRO_C \
                  || 1300 <= _MSC_VER)
               struct alignas_test { char c; char alignas (8) alignas_8; };