Disable generating movt on FreeBSD

[andrew]

Summary

The copy of binutils in FreeBSD is too old to correctly handle movt instructions. It is unlikely to be updated as newer versions are GPLv3. To fix this disable generating movt until a linker that can handle these is ready.

[dim]

@davide, any idea whether lld will be able to handle movt correctly? If so, we might want to make this dependent on -fuse-ld=bfd or -fuse-ld=lld ?

[emaste]

@davide, any idea whether lld will be able to handle movt correctly? If so, we might want to make this dependent on -fuse-ld=bfd or -fuse-ld=lld ?

I'm sure lld will handle everything we need eventually (if it does not already), but I'm not sure it's reasonable to have different behaviour based on -fuse-ld here anyhow -- ld.bfd may well be a recent one from ports.

[dim]

In D15791#317175, @emaste wrote:

@davide, any idea whether lld will be able to handle movt correctly? If so, we might want to make this dependent on -fuse-ld=bfd or -fuse-ld=lld ?

I'm sure lld will handle everything we need eventually (if it does not already), but I'm not sure it's reasonable to have different behaviour based on -fuse-ld here anyhow -- ld.bfd may well be a recent one from ports.

Right, so this really only applies for binutils ld below a certain version, then? IIRC the linker version on the system is detected at configuration time; maybe it can be used instead. Ideally there would be some sort of runtime detection, but it does not sound feasible with ld.

[davide]

In D15791#317172, @dim wrote:

@davide, any idea whether lld will be able to handle movt correctly? If so, we might want to make this dependent on -fuse-ld=bfd or -fuse-ld=lld ?

lld/AArch64 can't still handle that properly, so I'd rather recommend to make it dependent on fuse-ld=bfd.

Thanks,

Davide

[davide]

LGTM

lib/Driver/Tools.cpp

941

I'd add a FIXME I expect this to be fixed in the foreseeable future.

[andrew]

Can someone commit with the FIXME comment? I'm unable to do it myself.

[davide]

Close, this went in a while ago.

lib/Driver/Tools.cpp

static void getARMTargetFeatures(const ToolChain &TC,
   }
 
   // llvm does not support reserving registers in general. There is support
   // for reserving r9 on ARM though (defined as a platform-specific register
   // in ARM EABI).
   if (Args.hasArg(options::OPT_ffixed_r9))
     Features.push_back("+reserve-r9");
 
-  // The kext linker doesn't know how to deal with movw/movt.
-  if (KernelOrKext)
+  // The kext and FreeBSD linkers don't know how to deal with movw/movt.
+  if (KernelOrKext || Triple.isOSFreeBSD())
     Features.push_back("+no-movt");
 }
 
 void Clang::AddARMTargetArgs(const llvm::Triple &Triple, const ArgList &Args,
                              ArgStringList &CmdArgs, bool KernelOrKext) const {
   // Select the ABI to use.
   // FIXME: Support -meabi.
   // FIXME: Parts of this are duplicated in the backend, unify this somehow.

test/Driver/arm-no-movt.c

 // RUN: %clang -target armv7-apple-darwin -### %s 2>&1 \
 // RUN:    | FileCheck %s -check-prefix CHECK-DEFAULT
 
 // RUN: %clang -target armv7-apple-darwin -mkernel -### %s 2>&1 \
 // RUN:    | FileCheck %s -check-prefix CHECK-KERNEL
 
+// RUN: %clang -target armv7-gnueabi-freebsd11 -### %s 2>&1 \
+// RUN:    | FileCheck %s -check-prefix CHECK-FREEBSD
+
 // CHECK-DEFAULT-NOT: "-target-feature" "+no-movt"
 
 // CHECK-KERNEL: "-target-feature" "+no-movt"
+
+// CHECK-FREEBSD: "-target-feature" "+no-movt"