[Expat-bugs] [ expat-Patches-820946 ] expat.h not great for MSVC !cdecl deflt calling cnvntn

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Patches item #820946, was opened at 2003-10-09 19:06
Message generated for change (Comment added) made by kwaclaw
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Category: None
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Nobody/Anonymous (nobody)
Assigned to: Nobody/Anonymous (nobody)
Summary: expat.h not great for MSVC !cdecl deflt calling cnvntn

Initial Comment:
OK, well the title I wanted was "expat.h doesn't work
cleanly for MSVC with non-cdecl default calling
convetion", but there were (reasonable, I guess) length
limitations.

In any case, if you have a project in MSVC that has its
default calling convention set to something other than
cdecl (such as stdcall or fastcall), the prototypes for
the handler functions don't communicate that the
library is compiled to assume cdecl. Things will still
compile fine, however odd behavior occurs at runtime
(for example, my start element handler was called 5
times with the same name and then the thread crashed).
If your callback funcitons are then explicitly declared
cdecl (as they should be) then you have to use casts to
allow you to assign the address of your cdecl handler
functions to the function pointers that the compiler
defaults to the different convention.

I don't suppose many people bother to change the
default calling convention of their projects, but I
have seen fastcall give a 5% boost. XML parsing is not
a significant part of our apps exection time, so it's
not worth recompiling expat to fastcall. It would be
nice if it worked out of the box for us.

I've supplied a patch, that defines a macro XMLCALLBACK
for callbacks, much like the XMLPARSEAPI macro is
defined for API functions. I've tested it with MSVC 7.1
projects that default to both stdcall and fastcall.
Because the preprocessor tests are set up like the ones
for the XMLPARSEAPI macro, I don't think it should
affect any non-MSVC compilers.

Thanks,

Marsh Ray
marsh *period* ray *atsign* barrsystems *period* com


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>Comment By: Karl Waclawek (kwaclaw)
Date: 2003-10-11 16:10

Message:
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How does it work when you build the library
with your calling convention?

If it works OK then we should not force any
calling convention on the callbacks but simply
document that the pre-built binaries were compiled
with cdecl as default.

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