[PATCH] Makefile: fix build with binutils 2.38

[Aurelien Jarno]

>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        lib/sbi/sbi_tlb.o
<<BUILDDIR>>/lib/sbi/sbi_tlb.c: Assembler messages:
<<BUILDDIR>>/lib/sbi/sbi_tlb.c:190: Error: unrecognized opcode `fence.i'
make: *** [Makefile:431: <<BUILDDIR>>/build/lib/sbi/sbi_tlb.o] Error 1

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>
---
 Makefile | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

Changes v1 -> v2 following the review from Bin Men (thanks)!
- Fix typos
- Use grep to detect missing extensions for consistency with CC_SUPPORT_SAVE_RESTORE

diff --git a/Makefile b/Makefile
index 062883e..717dffd 100644
--- a/Makefile
+++ b/Makefile
@@ -153,6 +153,9 @@ OPENSBI_LD_PIE := $(shell $(CC) $(CLANG_TARGET) $(RELAX_FLAG) $(USE_LD_FLAG) -fP
 # Check whether the compiler supports -m(no-)save-restore
 CC_SUPPORT_SAVE_RESTORE := $(shell $(CC) $(CLANG_TARGET) $(RELAX_FLAG) -nostdlib -mno-save-restore -x c /dev/null -o /dev/null 2>&1 | grep "\-save\-restore" >/dev/null && echo n || echo y)
 
+# Check whether the assembler and the compiler support the Zicsr and Zifencei extensions
+CC_SUPPORT_ZICSR_ZIFENCEI := $(shell $(CC) $(CLANG_TARGET) $(RELAX_FLAG) -nostdlib -march=rv$(PLATFORM_RISCV_XLEN)imafd_zicsr_zifencei -x c /dev/null -o /dev/null 2>&1 | grep "zicsr\|zifencei" > /dev/null && echo n || echo y)
+
 # Build Info:
 # OPENSBI_BUILD_TIME_STAMP -- the compilation time stamp
 # OPENSBI_BUILD_COMPILER_VERSION -- the compiler version info
@@ -223,7 +226,11 @@ ifndef PLATFORM_RISCV_ABI
 endif
 ifndef PLATFORM_RISCV_ISA
   ifneq ($(PLATFORM_RISCV_TOOLCHAIN_DEFAULT), 1)
-    PLATFORM_RISCV_ISA = rv$(PLATFORM_RISCV_XLEN)imafdc
+    ifeq ($(CC_SUPPORT_ZICSR_ZIFENCEI), y)
+      PLATFORM_RISCV_ISA = rv$(PLATFORM_RISCV_XLEN)imafdc_zicsr_zifencei
+    else
+      PLATFORM_RISCV_ISA = rv$(PLATFORM_RISCV_XLEN)imafdc
+    endif
   else
     PLATFORM_RISCV_ISA = $(OPENSBI_CC_ISA)
   endif
-- 
2.34.1