[cfe-dev] [PATCH] Flexible array initializers may be strings

[Pierre Habouzit]

> For the record, clang accepts the following code:
> 
> -------8<-----------
> #include <stdio.h>
> 
> struct a {
>   int  i;
>   char v[];
> };
> 
> int main(void) {
>   struct a foo = { .i = 0, .v = "foo" };
>   struct a bar = { .i = 0, .v = { 'b', 'a', 'r', '\0' } };
> 
>   printf("%p %s\n", foo.v, foo.v);
>   printf("%p %s\n", bar.v, bar.v);
>   return 0;
> }
> -------8<-----------
> 
> whereas gcc rejects it with the error:
>   error: non-static initialization of a flexible array member
> 
> Clang doesn't complain, but generates invalid code though when foo and bar
> aren't static:
> 
> $ clang -o a a.c && ./a
> 0x7fff1eccc32c 
> 0x7fff1eccc324 ÿ
> 
> Reading the relevant parts of the bitcode indeed shows what is wrong:
> there is a correct internal constant for main.foo, but the variable
> foo storage is allocated using sizeof(struct a) instead of
> sizeof(main.foo), and the memcpy also uses sizeof(struct a) which is
> 4 instead of sizeof(main.foo).
> 
> @main.foo = internal constant %0 { i32 0, [4 x i8] c"foo\00" }, align 4
> %foo = alloca %struct.a, align 4
> call void @llvm.memcpy.p0i8.p0i8.i64(i8* %tmp, i8* bitcast (%0* @main.foo to i8*), i64 4, i32 4, i1 false)
> 
> Sadly fixing that exceeds my current clang hacking skills. Do you
> want me to report a bug for that ?

I made it http://llvm.org/bugs/show_bug.cgi?id=8217
-- 
·O·  Pierre Habouzit
··O                                                madcoder at debian.org
OOO                                                http://www.madism.org