riscv: Allow building with kcov coverage

Add ARCH_HAS_KCOV and HAVE_GCC_PLUGINS to the riscv Kconfig.
Also disable instrumentation of some early boot code and vdso.

Boot-tested on QEMU's riscv64 virt machine.
Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Acked-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

arch/riscv/Kconfig

@@ -19,6 +19,7 @@ config RISCV
 	select ARCH_HAS_DEBUG_WX
 	select ARCH_HAS_GCOV_PROFILE_ALL
 	select ARCH_HAS_GIGANTIC_PAGE
+	select ARCH_HAS_KCOV
 	select ARCH_HAS_MMIOWB
 	select ARCH_HAS_PTE_SPECIAL
 	select ARCH_HAS_SET_DIRECT_MAP
@@ -58,6 +59,7 @@ config RISCV
 	select HAVE_DMA_CONTIGUOUS if MMU
 	select HAVE_EBPF_JIT if MMU
 	select HAVE_FUTEX_CMPXCHG if FUTEX
+	select HAVE_GCC_PLUGINS
 	select HAVE_GENERIC_VDSO if MMU && 64BIT
 	select HAVE_PCI
 	select HAVE_PERF_EVENTS

arch/riscv/boot/Makefile

@@ -14,6 +14,8 @@
 # Based on the ia64 and arm64 boot/Makefile.
 #
 
+KCOV_INSTRUMENT := n
+
 OBJCOPYFLAGS_Image :=-O binary -R .note -R .note.gnu.build-id -R .comment -S
 
 targets := Image loader

arch/riscv/kernel/vdso/Makefile

@@ -32,6 +32,7 @@ CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE) -Os
 
 # Disable gcov profiling for VDSO code
 GCOV_PROFILE := n
+KCOV_INSTRUMENT := n
 
 # Force dependency
 $(obj)/vdso.o: $(obj)/vdso.so

arch/riscv/mm/Makefile

@@ -5,6 +5,8 @@ ifdef CONFIG_FTRACE
 CFLAGS_REMOVE_init.o = -pg
 endif
 
+KCOV_INSTRUMENT_init.o := n
+
 obj-y += init.o
 obj-y += extable.o
 obj-$(CONFIG_MMU) += fault.o pageattr.o