Re: Possible OS incompatibility with attribute 'shared'

LIU Hao via Gcc-help <[email protected]> Mon, 22 Dec 2025 16:48:00 +0800

Newsgroups	gmane.comp.gcc.help
Message-ID	<[email protected]>

在 2025-12-22 06:47, [email protected] 写道:
> Thanks, but that does not answer the question. The compiled code runs on BOTH systems. The only difference is that the method described does not work on Windows 7, whether the resulting executables are recompiled there or not. If it had never worked at all, I'd consider the choice of compiler version as relevant.

I don't have Windows 7 by hand, but I have tried it on Windows 11 and it works as expected. To check
whether the attribute is applied correctly, you may invoke `objdump -h` and look for the `SHARED` flag:

$ objdump -h value.dll

value.dll: file format pei-x86-64

Sections:
Idx Name Size VMA LMA File off Algn
0 .text 00001430 0000000209e11000 0000000209e11000 00000600 2**2
CONTENTS, ALLOC, LOAD, READONLY, CODE
1 .data 00000048 0000000209e13000 0000000209e13000 00001c00 2**2
CONTENTS, ALLOC, LOAD, DATA
2 share 00000004 0000000209e14000 0000000209e14000 00001e00 2**2
CONTENTS, ALLOC, LOAD, DATA, SHARED
...

The section is only shared by processes that load the same DLL file. It is not shared by processes that
load different copies of the DLL.

> The question is not about the versions of GCC. It's about the compatibility for the method as described, given that it works in one Windows OS but not the other. If this puts it beyond the scope of advice on GCC, how about some other simple way to share a single variable between processes using a hook DLL. I mention that because I'm trying to avopid making this an 'XY' problem (a phrase I see a lot on StackOverflow...)

You can use named shared memory for that purpose, passing a hard-coded UUID as a name. There's a tutorial
for it:

https://learn.microsoft.com/en-us/windows/win32/dlls/using-shared-memory-in-a-dynamic-link-library

--
Best regards,
LIU Hao

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