Commit Graph

10 Commits

Author SHA1 Message Date
David Majnemer 0c43d8077e AST: Initialization with dllimport functions in C
The C++ language requires that the address of a function be the same
across all translation units.  To make __declspec(dllimport) useful,
this means that a dllimported function must also obey this rule.  MSVC
implements this by dynamically querying the import address table located
in the linked executable.  This means that the address of such a
function in C++ is not constant (which violates other rules).

However, the C language has no notion of ODR nor does it permit dynamic
initialization whatsoever.  This requires implementations to _not_
dynamically query the import address table and instead utilize a wrapper
function that will be synthesized by the linker which will eventually
query the import address table.  The effect this has is, to say the
least, perplexing.

Consider the following C program:
__declspec(dllimport) void f(void);

typedef void (*fp)(void);

static const fp var = &f;

const fp fun() { return &f; }

int main() { return fun() == var; }

MSVC will statically initialize "var" with the address of the wrapper
function and "fun" returns the address of the actual imported function.
This means that "main" will return false!

Note that LLVM's optimizers are strong enough to figure out that "main"
should return true.  However, this result is dependent on having
optimizations enabled!

N.B.  This change also permits the usage of dllimport declarators inside
of template arguments; they are sufficiently constant for such a
purpose.  Add tests to make sure we don't regress here.

llvm-svn: 211677
2014-06-25 08:15:07 +00:00
Nico Rieck ffd8a3364c Sema: Add more tests for dll attributes on inline functions
llvm-svn: 209542
2014-05-23 19:07:49 +00:00
Hans Wennborg f436b2837c An inline function redeclaration does not drop the dllimport attribute
llvm-svn: 209449
2014-05-22 15:46:15 +00:00
Hans Wennborg b0f2f146bb Allow dllimport/dllexport on inline functions and adjust the linkage.
This is a step towards handling these attributes on classes (PR11170).

Differential Revision: http://reviews.llvm.org/D3772

llvm-svn: 208925
2014-05-15 22:07:49 +00:00
Nico Rieck 8ca0bfc57f Sema: Require external linkage for dll attributes
llvm-svn: 205198
2014-03-31 14:56:58 +00:00
Nico Rieck 82f0b06749 Sema: Check dll attributes on redeclarations
A redeclaration may not add dllimport or dllexport attributes. dllexport is
sticky and can be omitted on redeclarations while dllimport cannot.

llvm-svn: 205197
2014-03-31 14:56:15 +00:00
Nico Rieck 0854e59281 Fix tests in r204576
Proper redeclaration warnings for dllimport are not implemented yet.

llvm-svn: 204577
2014-03-23 22:07:53 +00:00
Nico Rieck e84f8db709 Treat dllimport globals without explicit storage class as extern
dllimport implies a definition which means the 'extern' keyword is optional
when declaring imported variables.

llvm-svn: 204576
2014-03-23 21:24:01 +00:00
Nico Rieck 8e9791f62c Sema: Definition of dllimport globals is not allowed
Upgrades the warning to an error and clarifies the message by treating the
definition as error instead of the attribute.

llvm-svn: 202300
2014-02-26 21:27:13 +00:00
Nico Rieck 6047866232 Reorganize and improve semantic tests for dllexport/import
llvm-svn: 201947
2014-02-22 19:47:30 +00:00