[PATCH 4.19] riscv: fix build with binutils 2.38

[Conor Dooley]

From: Aurelien Jarno <aurelien at aurel32.net>

commit 6df2a016c0c8a3d0933ef33dd192ea6606b115e3 upstream.

>From version 2.38, binutils default to ISA spec version 20191213. This
means that the csr read/write (csrr*/csrw*) instructions and fence.i
instruction has separated from the `I` extension, become two standalone
extensions: Zicsr and Zifencei. As the kernel uses those instruction,
this causes the following build failure:

  CC      arch/riscv/kernel/vdso/vgettimeofday.o
  <<BUILDDIR>>/arch/riscv/include/asm/vdso/gettimeofday.h: Assembler messages:
  <<BUILDDIR>>/arch/riscv/include/asm/vdso/gettimeofday.h:71: Error: unrecognized opcode `csrr a5,0xc01'
  <<BUILDDIR>>/arch/riscv/include/asm/vdso/gettimeofday.h:71: Error: unrecognized opcode `csrr a5,0xc01'
  <<BUILDDIR>>/arch/riscv/include/asm/vdso/gettimeofday.h:71: Error: unrecognized opcode `csrr a5,0xc01'
  <<BUILDDIR>>/arch/riscv/include/asm/vdso/gettimeofday.h:71: Error: unrecognized opcode `csrr a5,0xc01'

The fix is to specify those extensions explicitly in -march. However as
older binutils version do not support this, we first need to detect
that.

Signed-off-by: Aurelien Jarno <aurelien at aurel32.net>
Tested-by: Alexandre Ghiti <alexandre.ghiti at canonical.com>
Cc: stable at vger.kernel.org
Signed-off-by: Palmer Dabbelt <palmer at rivosinc.com>
[Conor: converted to the 4.19 style of march string generation]
Signed-off-by: Conor Dooley <conor.dooley at microchip.com>
---
CC: Palmer Dabbelt <palmer at dabbelt.com>
CC: linux-riscv at lists.infradead.org
CC: Greg Kroah-Hartman <gregkh at linuxfoundation.org>

lkp has yet to complain, so here you go Greg..

 arch/riscv/Makefile | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index 110be14e6122..b024029a2247 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -49,9 +49,16 @@ ifeq ($(CONFIG_RISCV_ISA_C),y)
 	KBUILD_ARCH_C = c
 endif
 
-KBUILD_AFLAGS += -march=$(KBUILD_MARCH)$(KBUILD_ARCH_A)fd$(KBUILD_ARCH_C)
+# Newer binutils versions default to ISA spec version 20191213 which moves some
+# instructions from the I extension to the Zicsr and Zifencei extensions.
+toolchain-need-zicsr-zifencei := $(call cc-option-yn, -march=$(riscv-march-y)_zicsr_zifencei)
+ifeq ($(toolchain-need-zicsr-zifencei),y)
+	KBUILD_ARCH_ZISCR_ZIFENCEI = _zicsr_zifencei
+endif
+
+KBUILD_AFLAGS += -march=$(KBUILD_MARCH)$(KBUILD_ARCH_A)fd$(KBUILD_ARCH_C)$(KBUILD_ARCH_ZISCR_ZIFENCEI)
 
-KBUILD_CFLAGS += -march=$(KBUILD_MARCH)$(KBUILD_ARCH_A)$(KBUILD_ARCH_C)
+KBUILD_CFLAGS += -march=$(KBUILD_MARCH)$(KBUILD_ARCH_A)$(KBUILD_ARCH_C)$(KBUILD_ARCH_ZISCR_ZIFENCEI)
 KBUILD_CFLAGS += -mno-save-restore
 KBUILD_CFLAGS += -DCONFIG_PAGE_OFFSET=$(CONFIG_PAGE_OFFSET)
 
-- 
2.37.3