[llvm-bugs] [Bug 24927] New: LC_VERSION_MIN_MACOSX: Darwin kernel version vs SDK version

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=24927

            Bug ID: 24927
           Summary: LC_VERSION_MIN_MACOSX: Darwin kernel version vs SDK
                    version
           Product: libraries
           Version: trunk
          Hardware: Macintosh
                OS: MacOS X
            Status: NEW
          Severity: normal
          Priority: P
         Component: Common Code Generator Code
          Assignee: unassignedbugs at nondot.org
          Reporter: benoit.belley at autodesk.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

Using the Xcode 7 linker, one gets messages such as the following when linking
objects generated using llvm:

ld: warning: object file (foo.o) was built for newer OS X version (14.5) than
being linked (10.9)

The issue is the following:

a) In lib/Support/Unix/Host.inc, sys::getDefaultTargetTriple() sets the OS name
to darwin14.5 when running on MaxOS X 10.10. 14.5 is the Darwin kernel version
as reported by uname.

b) In lib/CodeGen/AsmPrinter.cpp, AsmPrinter::doInitialization() writes out
this version number to the LC_VERSION_MIN_MACOSX of the generated object.

c) The XCode 7 linker seems to expect that LC_VERSION_MIN_MACOSX contains the
minimum version number of the MacOS X SDK (10.9, 10.11, ...), NOT the Darwin
kernel version number! 

AFAICT, LLVM had this wrong behaviour for a long time. The only new thing with
the Xcode 7 linker is that it is now reporting a warning for the version
mismatch.

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