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<p>Some replies inline:</p>
<p><br>
</p>
<div class="moz-cite-prefix">On 06/09/2022 15:08, Manuel
Bleichenbacher wrote:<br>
</div>
<blockquote type="cite" cite="mid:CAA7F5jKb2H=D0dDa2EuDSzg4wb6Qm4TGpFpzJNbskxf1--rdtw@mail.gmail.com">
<div dir="ltr">
<div>I think there are only a few cases:</div>
<div><br>
</div>
<div>
<div>Case 1: extern int i;</div>
<div>It is a declaration and should generate the lookup for a
symbol "i" (plus a method to get the value). It is already
implemented like this.<br>
</div>
</div>
</div>
</blockquote>
I agree this is the most idiomatic way to do things.<br>
<blockquote type="cite" cite="mid:CAA7F5jKb2H=D0dDa2EuDSzg4wb6Qm4TGpFpzJNbskxf1--rdtw@mail.gmail.com">
<div dir="ltr">
<div>
<div><br>
</div>
Case 2: int i = 4;</div>
<div>It can be skipped as it never appears in a header file that
can be consumed by multiple compilation units (as it would
generate an error). It's simply not relevant for jextract,
which generates code to access an existing library.<br>
</div>
<div><br>
</div>
<div>Case 3: int i;</div>
<div>It is the same as case 2 (implicitly initializes to 0).</div>
</div>
</blockquote>
<p>I also agree that these two seem suspicious. While in a
standalone application, an header containg symbols like these
might make sense, in a library, this most likely does not make any
sense, as it will create storage in all clients importing the
headerfile.</p>
<p><br>
</p>
<blockquote type="cite" cite="mid:CAA7F5jKb2H=D0dDa2EuDSzg4wb6Qm4TGpFpzJNbskxf1--rdtw@mail.gmail.com">
<div dir="ltr">
<div><br>
</div>
Case 4: int __declspec(selectany) i = 4;<br>
<div>This is a special case *and most likely Microsoft
specific). In theory, the behavior could be replicated, i.e. a
variable or constant is allocated in native memory and
properly initialized. Since it's a rare case, I'd rather skip
it.</div>
</div>
</blockquote>
<p>Yes, this seems to be special and unique to Windows. But, I'd
rather gate on presence of "extern", than to obscure __declspec.</p>
<p><br>
</p>
<br>
<blockquote type="cite" cite="mid:CAA7F5jKb2H=D0dDa2EuDSzg4wb6Qm4TGpFpzJNbskxf1--rdtw@mail.gmail.com">
<div dir="ltr">
<div><br>
</div>
<div>Case 5: static int i = 4;</div>
<div>It is a mixture between case 2 and 4. It's unlikely to
appear in header files although it does not generate an error.
The behavior could be replicated but I would spend time on
more important things and skip it for now.</div>
<div><br>
</div>
<div>Case 6: static int i;</div>
<div>It is the same as case 5 (implicitly initializes to 0).<br>
</div>
</div>
</blockquote>
<p>These seem easier, since declaration says "static".</p>
<p><br>
</p>
<p>It seems to me that all this boil to two rules:<br>
</p>
<p>* we should only generate global var accessor for "extern"
variables<br>
* we should skip static symbols (this is covered by [1])</p>
<p>Maurizio</p>
<p>[1] - <a class="moz-txt-link-freetext" href="https://github.com/openjdk/jextract/pull/70">https://github.com/openjdk/jextract/pull/70</a><br>
</p>
<p><br>
</p>
<blockquote type="cite" cite="mid:CAA7F5jKb2H=D0dDa2EuDSzg4wb6Qm4TGpFpzJNbskxf1--rdtw@mail.gmail.com"><br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Tue, Sep 6, 2022 at 3:29 PM
Maurizio Cimadamore <<a href="mailto:maurizio.cimadamore@oracle.com" moz-do-not-send="true" class="moz-txt-link-freetext">maurizio.cimadamore@oracle.com</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div>
<p>Hi,<br>
I think there's more to it.</p>
<p>On Linux, if I do the following:</p>
<p>```<br>
$ cat foo.h<br>
int i = 4;<br>
```<br>
</p>
<p>and:</p>
<p>```<br>
$ cat foo.c<br>
#include "foo.h"<br>
```<br>
</p>
<p>And then I compile into a shared lib, the obtained foo.so
does have a symbol for "i" (rightfully so):<br>
</p>
<p>```<br>
$ objdump -T foo.so<br>
<br>
foo.so: file format elf64-x86-64<br>
<br>
DYNAMIC SYMBOL TABLE:<br>
0000000000000000 w D *UND* 0000000000000000
__cxa_finalize<br>
0000000000000000 w D *UND* 0000000000000000
_ITM_registerTMCloneTable<br>
0000000000000000 w D *UND* 0000000000000000
_ITM_deregisterTMCloneTable<br>
0000000000000000 w D *UND* 0000000000000000
__gmon_start__<br>
0000000000004020 g DO .data 0000000000000004 i<br>
<br>
```</p>
<p>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).<br>
</p>
<p>Maurizio<br>
</p>
<p><br>
</p>
<div>On 06/09/2022 13:57, Manuel Bleichenbacher wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">
<div>There are two indications that it's definition and
not a declaration:</div>
<div><br>
</div>
<div>- absence of "extern" keyword</div>
<div>- presence of initialization ( = { 0x... )</div>
<div><br>
</div>
<div>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.</div>
<div><br>
</div>
<div>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. </div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Tue, Sep 6, 2022 at
12:11 PM Maurizio Cimadamore <<a href="mailto:maurizio.cimadamore@oracle.com" target="_blank" moz-do-not-send="true" class="moz-txt-link-freetext">maurizio.cimadamore@oracle.com</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px
0px 0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex"><br>
On 05/09/2022 16:32, Manuel Bleichenbacher wrote:<br>
> extern "C" const GUID __declspec(selectany)
GUID_DEVINTERFACE_USB_DEVICE<br>
> = { 0xA5DCBF10L, 0x6530, 0x11D2, { 0x90,
0x1F, 0x00, 0xC0, <br>
> 0x4F, 0xB9, 0x51, 0xED } };<br>
><br>
I guess the problem here is the lack of "dllexport",
right?<br>
<br>
But, while dllexport is common, some libraries can
still export symbols <br>
using a .def file [1].<br>
<br>
So, I'm not sure this belongs in the same category as
"static inline", <br>
as it is not possible, just by looking at the header,
to understand <br>
whether the symbol will be present or not?<br>
<br>
[1] - <br>
<a href="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$" rel="noreferrer" target="_blank" moz-do-not-send="true">https://docs.microsoft.com/en-us/cpp/build/exporting-from-a-dll-using-def-files?view=msvc-170</a><br>
<br>
</blockquote>
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