https://bugs.llvm.org/show_bug.cgi?id=46886
Bug ID: 46886
Summary: Clang does not set /DEFAULTLIB:OLDNAMES when invoking
link.exe on Windows
Product: new-bugs
Version: unspecified
Hardware: PC
OS: Windows NT
Status: NEW
Severity: enhancement
Priority: P
Component: new bugs
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected]
Created attachment 23787
--> https://bugs.llvm.org/attachment.cgi?id=23787&action=edit
Test case
When using Clang together with the Windows SDK, Clang doesn't set
"/DEFAULTLIB:OLDNAMES" when invoking "link.exe". This flag is required in order
to access various standard C functions ("_fdopen", "_atoi64") through their
"deprecated" names ("fdopen", "atoi64"). For comparison, "cl.exe" sets this
flag by default when invoking "link.exe", unless told not to (for example, by
passing "/NODEFAULTLIB".
If this option is not passed, programs that access the functions through their
alternate name will fail at link-time with an undefined reference error (at
least with Clang's default configuration, the function declarations appear to
always be defined).
>From a user perspective, this is highly confusing, since a casual internet
search doesn't reveal why such functions would throw linker errors. I was
tipped off by looking at the Mingw project's source code, since it seems to do
something similar.
Attached is a program that demonstrates the error. It will fail to compile when
run in a Clang+Windows SDK environment:
clang example.c
but succeed when run with "--for-linker=-DEFAULTLIB:OLDNAMES":
clang --for-linker=-DEFAULTLIB:OLDNAMES example.c
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