Build changes that allow the modules on arm64.

- Move the required kernel compiler flags from Makefile.arm64 to kern.mk.
- Build arm64 modules as PIC; non-PIC relocations in .o for shared object
  output cannot be handled.
- Do not try to install aarch64 symlink.
- A hack for arm64 to avoid ld -r stage.  See the comment for the explanation.
  Some functionality is lost, like ctf handling, but hopefully will be
  restored after newer linker is available.

Reviewed by:	andrew, emaste
Tested by:	andrew (on real hardware)
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D3796

5 files changed, 23 insertions, 9 deletions

diff --git a/sys/arm64/conf/GENERIC b/sys/arm64/conf/GENERIC
index 26ca51df86ac..1486f0793686 100644
--- a/sys/arm64/conf/GENERIC
+++ b/sys/arm64/conf/GENERIC
@@ -22,7 +22,6 @@ cpu		ARM64
 ident		GENERIC
 
 makeoptions	DEBUG=-g		# Build kernel with gdb(1) debug symbols
-makeoptions	NO_MODULES=1		# We don't yet support modules on arm64
 
 options 	SCHED_ULE		# ULE scheduler
 options 	PREEMPTION		# Enable kernel thread preemption
diff --git a/sys/conf/Makefile.arm64 b/sys/conf/Makefile.arm64
index 46c191c5c121..324daa7cf17f 100644
--- a/sys/conf/Makefile.arm64
+++ b/sys/conf/Makefile.arm64
@@ -27,12 +27,6 @@ S=	../../..
 
 INCLUDES+= -I$S/contrib/libfdt
 
-# We generally don't want fpu instructions in the kernel.
-CFLAGS += -mgeneral-regs-only
-
-# Reserve x18 for pcpu data
-CFLAGS += -ffixed-x18
-
 .if !empty(DDB_ENABLED)
 CFLAGS += -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer
 .endif
diff --git a/sys/conf/kern.mk b/sys/conf/kern.mk
index 7f1c0265512a..56ddbda4996e 100644
--- a/sys/conf/kern.mk
+++ b/sys/conf/kern.mk
@@ -97,6 +97,13 @@ INLINE_LIMIT?=	8000
 INLINE_LIMIT?=	8000
 .endif
 
+.if ${MACHINE_CPUARCH} == "aarch64"
+# We generally don't want fpu instructions in the kernel.
+CFLAGS += -mgeneral-regs-only
+# Reserve x18 for pcpu data
+CFLAGS += -ffixed-x18
+.endif
+
 #
 # For sparc64 we want the medany code model so modules may be located
 # anywhere in the 64-bit address space.  We also tell GCC to use floating
diff --git a/sys/conf/kern.post.mk b/sys/conf/kern.post.mk
index 0703cc82347b..55b4fd7a21ea 100644
--- a/sys/conf/kern.post.mk
+++ b/sys/conf/kern.post.mk
@@ -212,7 +212,7 @@ SRCS=	assym.s vnode_if.h ${BEFORE_DEPEND} ${CFILES} \
 	mv .newdep .depend
 
 _ILINKS= machine
-.if ${MACHINE} != ${MACHINE_CPUARCH}
+.if ${MACHINE} != ${MACHINE_CPUARCH} && ${MACHINE} != "arm64"
 _ILINKS+= ${MACHINE_CPUARCH}
 .endif
 .if ${MACHINE_CPUARCH} == "i386" || ${MACHINE_CPUARCH} == "amd64"
diff --git a/sys/conf/kmod.mk b/sys/conf/kmod.mk
index 47bc593b0018..06e4cfcdc1f4 100644
--- a/sys/conf/kmod.mk
+++ b/sys/conf/kmod.mk
@@ -113,6 +113,10 @@ CFLAGS+=	${DEBUG_FLAGS}
 CFLAGS+=	-fno-omit-frame-pointer -mno-omit-leaf-frame-pointer
 .endif
 
+.if ${MACHINE_CPUARCH} == "aarch64"
+CFLAGS+=	-fPIC
+.endif
+
 # Temporary workaround for PR 196407, which contains the fascinating details.
 # Don't allow clang to use fpu instructions or registers in kernel modules.
 .if ${MACHINE_CPUARCH} == arm
@@ -182,7 +186,17 @@ ${PROG}.debug: ${FULLPROG}
 
 .if ${__KLD_SHARED} == yes
 ${FULLPROG}: ${KMOD}.kld
+.if ${MACHINE_CPUARCH} != "aarch64"
 	${LD} -Bshareable ${_LDFLAGS} -o ${.TARGET} ${KMOD}.kld
+.else
+#XXXKIB Relocatable linking in aarch64 ld from binutils 2.25.1 does
+#       not work.  The linker corrupts the references to the external
+#       symbols which are defined by other object in the linking set
+#       and should therefore loose the GOT entry.  The problem seems
+#       to be fixed in the binutils-gdb git HEAD as of 2015-10-04.  Hack
+#       below allows to get partially functioning modules for now.
+	${LD} -Bshareable ${_LDFLAGS} -o ${.TARGET} ${OBJS}
+.endif
 .if !defined(DEBUG_FLAGS)
 	${OBJCOPY} --strip-debug ${.TARGET}
 .endif
@@ -220,7 +234,7 @@ ${FULLPROG}: ${OBJS}
 .endif
 
 _ILINKS=machine
-.if ${MACHINE} != ${MACHINE_CPUARCH}
+.if ${MACHINE} != ${MACHINE_CPUARCH} && ${MACHINE} != "arm64"
 _ILINKS+=${MACHINE_CPUARCH}
 .endif
 .if ${MACHINE_CPUARCH} == "i386" || ${MACHINE_CPUARCH} == "amd64"