How to compile dhrystone benchmark for RV32I

Question

when i am trying to compile the dhrystone benchmark in riscv-sodor for -march RV32I, an unrecognized opcode 'amoadd' error exits the compilation.

riscv-gcc -m32 -Wa,-march=RV32I -std=gnu99 -O2 -nostdlib -nostartfiles  -DPREALLOCATE=1 -DHOST_DEBUG=0 \
                 -c -I../env -I./common -I./dhrystone ./dhrystone/dhrystone_main.c -o dhrystone_main.o
In file included from ./dhrystone/dhrystone_main.c:12:0:
./common/util.h:11:0: warning: "rdcycle" redefined [enabled by default]
./dhrystone/dhrystone.h:385:0: note: this is the location of the previous definition
/tmp/ccDLKK6P.s: Assembler messages:
/tmp/ccDLKK6P.s:16: Error: unrecognized opcode `amoadd'
make: *** [dhrystone_main.o] Error 1

Is there any way to compile the dhrystone for baremetal hardware of RV32I.

Answer 1

Remove the -Wa,-march=RV32I flag.

-Wa,-march=RV32I is telling the assembler to only accept valid RV32I instructions. It has found an amoadd instruction, so it properly errored out. The assembler is in no position to change out invalid instructions for valid instructions, that's the compiler's job.

Unfortunately, as of 2014 Dec, the riscv-toolchain's gcc port does not yet support -march=RV32I .

Instead, it is on the programmer to personally avoid writing code that will emit multiplies, AMOs, floating point, etc. In fact, the provided dhrystone code includes floating point instructions (I believe only in the initialization code) which would also cause -Wa,-march=RV32I to fail as well. In this situation, the programmer of dhrystone checks whether the processor supports floating point instructions and branches around them as required.

On a more academic note, I believe the amoadd is coming in from the common/util.h's "barrier" implementation. However, since dhrystone does not call barrier, I'm unsure why the assembler is being passed an amoadd instruction. I certainly don't see it in my own disassemblies of dhrystone. I also was unable to reproduce your error on my own RISCV compilers. I am using a riscv-gcc from early August 2014 ( https://github.com/ucb-bar/riscv-tools ) and a newer gcc4.9 found at ( https://github.com/ucb-bar/riscv-tools/tree/new-abi ), which is in testing, but will soon be moved to master (~Jan 2015).