Question

I use Visual Studio 2008 and have a question regarding this warning.

In one of our libraries, we set the “Fixed Base address” flag (/FIXED) and have a fixed base address defined.

We declare a shared section with the commands

#pragma comment(linker,"/SECTION:FOO,RWS") 
#pragma data_seg("FOO")

When I remove the /FIXED flag I get the warning

LINK : warning LNK4092: shared writable section ‘FOO’ contains relocations; image may not run correctly

I understand, that with this flag, the dll might be relocated, when loading from an executable.
Now what I don’t understand. Why is it important, that these shared sections are not relocated? Are those addresses not virtual for each process?

Is there any way to allow relocations and have a shared section? We had a problem with this after we changed the library interface and I want to avoid this in the future, if any developer changes this library without knowledge of these consequences.

I am also curious how this works. The MSDNA page for the /SECTION flag and the 4092 warning are not very helpful here.

Answer 1

I believe KB137235 is relevant here. Basically the error is telling you that the section contains data that depends on the address the section is loaded at, such as a pointer to other data in the section. If the section is relocatable, different instances might not be at the same virtual address, so the pointer can’t be valid for all of them simultaneously.

In the medium-to-long term, the correct solution is to not use a shared section. See, for example:

• Appendix G: SDL Requirement: No Shared Sections
• The Old New Thing: Why .shared sections are a security hole
• KB147136: Problem with Shared Data Sections in DLLs