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

[Pierre Habouzit]

for example:

struct a {
  int  b;
  char v[];
};

struct a foo = { .b = 0, .v = "bar" };

is perfectly sensible and correct (and accepted by gcc).

Signed-off-by: Pierre Habouzit <madcoder at debian.org>
---
 lib/Sema/SemaInit.cpp |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)


    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 ?

declare i32 @printf(i8*, ...)

diff --git a/lib/Sema/SemaInit.cpp b/lib/Sema/SemaInit.cpp
index 1ffa702..916134e 100644
--- a/lib/Sema/SemaInit.cpp
+++ b/lib/Sema/SemaInit.cpp
@@ -1461,7 +1461,7 @@ InitListChecker::CheckDesignatedInitializer(const InitializedEntity &Entity,
         Invalid = true;
       }
 
-      if (!hadError && !isa<InitListExpr>(DIE->getInit())) {
+      if (!hadError && !isa<InitListExpr>(DIE->getInit()) && !isa<StringLiteral>(DIE->getInit())) {
         // The initializer is not an initializer list.
         SemaRef.Diag(DIE->getInit()->getSourceRange().getBegin(),
                       diag::err_flexible_array_init_needs_braces)
-- 
1.7.2.2.566.g36af9