static inline and jextract

[Maurizio Cimadamore]

Hi,
I think there's more to it.

On Linux, if I do the following:

```
$ cat foo.h
int i = 4;
```

and:

```
$ cat foo.c
#include "foo.h"
```

And then I compile into a shared lib, the obtained foo.so does have a 
symbol for "i" (rightfully so):

```
$ objdump -T foo.so

foo.so:     file format elf64-x86-64

DYNAMIC SYMBOL TABLE:
0000000000000000  w   D  *UND*    0000000000000000 __cxa_finalize
0000000000000000  w   D  *UND*    0000000000000000 _ITM_registerTMCloneTable
0000000000000000  w   D  *UND*    0000000000000000 
_ITM_deregisterTMCloneTable
0000000000000000  w   D  *UND*    0000000000000000 __gmon_start__
0000000000004020 g    DO .data    0000000000000004 i

```

E.g. the above header contains a *definition*, so the compiler will 
create storage for it (and add it to the shared library), and "i" can be 
looked up in the shared lib. Conversely, a global marked as "extern" 
might or might not be present in the shared library (depending on 
whether it's defined in one of the associated C/CPP files).

Maurizio


On 06/09/2022 13:57, Manuel Bleichenbacher wrote:
> There are two indications that it's definition and not a declaration:
>
> - absence of "extern" keyword
> - presence of initialization ( = { 0x... )
>
> If it was compiled as C/C++ code, it would allocate memory in the 
> current compilation unit while a declaration would just refer to 
> something outside the compilation unit.
>
> Definitions are rare in header files as they usually lead to duplicate 
> symbol errors at link time. But through the magic of 
> __declspec(selectany), this is avoided.
>
> On Tue, Sep 6, 2022 at 12:11 PM Maurizio Cimadamore 
> <maurizio.cimadamore at oracle.com> wrote:
>
>
>     On 05/09/2022 16:32, Manuel Bleichenbacher wrote:
>     > extern "C" const GUID __declspec(selectany)
>     GUID_DEVINTERFACE_USB_DEVICE
>     >     = { 0xA5DCBF10L, 0x6530, 0x11D2, { 0x90, 0x1F,  0x00,  0xC0,
>     >  0x4F,  0xB9,  0x51,  0xED } };
>     >
>     I guess the problem here is the lack of "dllexport", right?
>
>     But, while dllexport is common, some libraries can still export
>     symbols
>     using a .def file [1].
>
>     So, I'm not sure this belongs in the same category as "static
>     inline",
>     as it is not possible, just by looking at the header, to understand
>     whether the symbol will be present or not?
>
>     [1] -
>     https://docs.microsoft.com/en-us/cpp/build/exporting-from-a-dll-using-def-files?view=msvc-170
>     <https://urldefense.com/v3/__https://docs.microsoft.com/en-us/cpp/build/exporting-from-a-dll-using-def-files?view=msvc-170__;!!ACWV5N9M2RV99hQ!IZ9OZ1GPWyZCLxdiYrnGJewYmhC_BCpH8sxH4Lo2jBtSsuMJPH_j3-vIXRO1emIKo2SMrT3Sj1AqI3daPLx2VOq6oGrpPgb-Xw$>
>
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