commit 4b12e104932c799881b917fc4c15b9508cfe64d1
Author: Brandon Bergren <git@bdragon.rtk0.net>
Date:   Thu Nov 7 18:27:48 2019 -0600

    WIP, FINISH ME AND SEND: Disable TOC optimization in kernel modules.

diff --git a/contrib/llvm/tools/lld/ELF/Arch/PPC64.cpp b/contrib/llvm/tools/lld/ELF/Arch/PPC64.cpp
index 0f382dcd6b3..f95e2e35e03 100644
--- a/contrib/llvm/tools/lld/ELF/Arch/PPC64.cpp
+++ b/contrib/llvm/tools/lld/ELF/Arch/PPC64.cpp
@@ -171,6 +171,7 @@ bool elf::tryRelaxPPC64TocIndirection(RelType type, const Relocation &rel,
       config->isLE ? getRelaTocSymAndAddend<ELF64LE>(tocISB, rel.addend)
                    : getRelaTocSymAndAddend<ELF64BE>(tocISB, rel.addend);
 
+  // XXX Figure out why linker sets in kernel modules aren't triggering this!
   // Only non-preemptable defined symbols can be relaxed.
   if (!d || d->isPreemptible)
     return false;
diff --git a/contrib/llvm/tools/lld/ELF/Writer.cpp b/contrib/llvm/tools/lld/ELF/Writer.cpp
index 10b171e8c0d..6d012655fd5 100644
--- a/contrib/llvm/tools/lld/ELF/Writer.cpp
+++ b/contrib/llvm/tools/lld/ELF/Writer.cpp
@@ -2006,6 +2006,8 @@ void Writer<ELFT>::addStartStopSymbols(OutputSection *sec) {
   StringRef s = sec->name;
   if (!isValidCIdentifier(s))
     return;
+  // XXX Allow programs to define STV_DEFAULT visibility, FreeBSD needs
+  // this for the vnet and dpcpu linker sets!
   addOptionalRegular(saver.save("__start_" + s), sec, 0, STV_PROTECTED);
   addOptionalRegular(saver.save("__stop_" + s), sec, -1, STV_PROTECTED);
 }
diff --git a/sys/conf/kmod.mk b/sys/conf/kmod.mk
index 5443f1ce2a2..24e70e8fedc 100644
--- a/sys/conf/kmod.mk
+++ b/sys/conf/kmod.mk
@@ -175,6 +175,27 @@ CFLAGS+=	-funwind-tables
 
 .if ${MACHINE_CPUARCH} == powerpc
 CFLAGS+=	-mlongcall -fno-omit-frame-pointer
+# Don't apply TOC optimizations in kernel modules.
+#
+# As per ELFv2 ABI spec section 3.6, the linker is allowed to perform several
+# optimizations during link to reduce indirection. We explicitly rely on
+# being able to relocate linker sets separately from the rest of the program
+# by applying relocations to the TOC directly.
+# LLD 9 and above assume that the relative displacement of "local" symbols
+# will not change, and relax GOT-indirect access to be TOC-relative
+# from r2 when the target address is in displacement range.
+# Unfortunately, this does not hold true for the set_vnet and set_pcpu
+# linker_sets, which both are manually processed by the in-kernel linker
+# to be assigned offsets dynamically, and as such, references to symbols in
+# these sections MUST continue to be via the TOC.
+#
+# XXX REWORD THIS BEFORE SUBMITTING! (Figure out where I mean to say GOT instead of TOC!)
+#
+# As such, disable toc optimization on modules until we have a more targeted
+# method for preserving the indirection for these linker sets.
+. if ${LINKER_TYPE} == "lld" && ${LINKER_VERSION} >= 90000
+LDFLAGS+=	--no-toc-optimize
+. endif
 .endif
 
 .if ${MACHINE_CPUARCH} == mips
diff --git a/sys/kern/link_elf.c b/sys/kern/link_elf.c
index 5975f13b9fd..97aa56c18d0 100644
--- a/sys/kern/link_elf.c
+++ b/sys/kern/link_elf.c
@@ -424,6 +424,7 @@ link_elf_init(void* arg)
 	ef = (elf_file_t) linker_kernel_file;
 	ef->preloaded = 1;
 #ifdef __powerpc__
+/* XXX double check */
 	ef->address = (caddr_t) (__startkernel - KERNBASE);
 #else
 	ef->address = 0;
@@ -436,6 +437,7 @@ link_elf_init(void* arg)
 	if (dp != NULL)
 		parse_dynamic(ef);
 #ifdef __powerpc__
+/* XXX double check */
 	linker_kernel_file->address = (caddr_t)__startkernel;
 	linker_kernel_file->size = (intptr_t)(__endkernel - __startkernel);
 #else
diff --git a/sys/sys/linker_set.h b/sys/sys/linker_set.h
index 9f49b802887..72e703d46e6 100644
--- a/sys/sys/linker_set.h
+++ b/sys/sys/linker_set.h
@@ -42,8 +42,9 @@
  * For ELF, this is done by constructing a separate segment for each set.
  */
 
-#if defined(__powerpc64__)
+#if defined(__powerpc64__) && (!defined(_CALL_ELF) || _CALL_ELF == 1)
 /*
+ * ELFv1 pointers to functions are actaully pointers to function descriptors.
  * Move the symbol pointer from ".text" to ".data" segment, to make
  * the GCC compiler happy:
  */