[llvm-bugs] [Bug 49681] New: ObjC relocation against symbol in discarded section error on Windows using gnustep-2.0 runtime

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=49681

            Bug ID: 49681
           Summary: ObjC relocation against symbol in discarded section
                    error on Windows using gnustep-2.0 runtime
           Product: clang
           Version: 11.0
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: normal
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: frederik at algoriddim.com
                CC: htmldeveloper at gmail.com, llvm-bugs at lists.llvm.org,
                    neeilans at live.com, richard-llvm at metafoo.co.uk

Linking a file that references functions from the gnustep-2.0 runtime, but does
not reference any Objective-C code, results in the following linker errors when
using LLD:

lld-link: error: relocation against symbol in discarded section:
__start_.objcrt$SEL
>>> referenced by test-ffaa49.o:(.objc_init)

lld-link: error: relocation against symbol in discarded section:
__stop.objcrt$SEL
>>> referenced by test-ffaa49.o:(.objc_init)

lld-link: error: relocation against symbol in discarded section:
__start_.objcrt$CLS
>>> referenced by test-ffaa49.o:(.objc_init)

lld-link: error: relocation against symbol in discarded section:
__stop.objcrt$CLS
>>> referenced by test-ffaa49.o:(.objc_init)

lld-link: error: relocation against symbol in discarded section:
__start_.objcrt$CLR
>>> referenced by test-ffaa49.o:(.objc_init)

lld-link: error: relocation against symbol in discarded section:
__stop.objcrt$CLR
>>> referenced by test-ffaa49.o:(.objc_init)

lld-link: error: relocation against symbol in discarded section:
__start_.objcrt$CAT
>>> referenced by test-ffaa49.o:(.objc_init)

lld-link: error: relocation against symbol in discarded section:
__stop.objcrt$CAT
>>> referenced by test-ffaa49.o:(.objc_init)

lld-link: error: relocation against symbol in discarded section:
__start_.objcrt$PCL
>>> referenced by test-ffaa49.o:(.objc_init)

lld-link: error: relocation against symbol in discarded section:
__stop.objcrt$PCL
>>> referenced by test-ffaa49.o:(.objc_init)

lld-link: error: relocation against symbol in discarded section:
__start_.objcrt$PCR
>>> referenced by test-ffaa49.o:(.objc_init)

lld-link: error: relocation against symbol in discarded section:
__stop.objcrt$PCR
>>> referenced by test-ffaa49.o:(.objc_init)

lld-link: error: relocation against symbol in discarded section:
__start_.objcrt$CAL
>>> referenced by test-ffaa49.o:(.objc_init)

lld-link: error: relocation against symbol in discarded section:
__stop.objcrt$CAL
>>> referenced by test-ffaa49.o:(.objc_init)

lld-link: error: relocation against symbol in discarded section:
__start_.objcrt$STR
>>> referenced by test-ffaa49.o:(.objc_init)

lld-link: error: relocation against symbol in discarded section:
__stop.objcrt$STR
>>> referenced by test-ffaa49.o:(.objc_init)
clang: error: linker command failed with exit code 1 (use -v to see invocation)


Using link.exe only results in the following warnings:

libcmt.lib(exe_main.obj) : warning LNK4078: multiple '.CRT' sections found with
different attributes (40400040)
libcmt.lib(initializers.obj) : warning LNK4254: section '.CRT' (C0000040)
merged into '.rdata' (40000040) with different attributes


This can be reproduced e.g. as follows:

$ cat test.m
#include <objc/runtime.h>

int main(int argc, char *argv[]) {
  objc_getClass("Test");
}

$ clang -fobjc-runtime=gnustep-2.0 -fuse-ld=lld -lobjc test.m


Adding any code that references Objective-C classes in the same file, e.g.
`[NSObject new]`, makes the linker errors disappear. Likewise using the
gnustep-1.9 runtime does not expose this issue.


This is relevant when using Autoconf to check for the existence of runtime
functions, as it will generate files like the above (minus the #include) to do
so.

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