Hi, guys
we aim to self make a FPU which has its own instruction set. For easy
programming, we prefer c language to assembly code.
here's one of our instruction:
c language format: Bload(vd, value1, value2), we make it like a
funciton. vd is a special register.
binary format: 31-26 opcode, 25-21 index of vd register, 20-16 opcode,
15-11 index of the general register which keeps value1, 10-5 opcode, 4-0
index of the general register which keeps value2.
we use gcc-inline-assembly to convert it to binary code. here's the
solution:
#define Bload(vd, value1, value2) \
__asm__( \
"add r16, r0, %0 \n\t" \
"add r14, r0, %1 \n\t" \
".long %2 \n\t" \
: \
: "r"(value2), "r"(value1),
"i"((0x3b<<26)+(vd<<21)+(14<<11)+(0x2c<<5)+16) \
: "r14", "r16");
i fix the general registers(r14, r16) which keep value1 and value2. then
i make the binary code use "i" in inline-assembly. But disadvantage is
in evidence: gcc does not understand my instruction, so i can not take
it's advantage, such as selecting the most suitable general register and
eliminating unnecessary copy from register to register.
what i want is deleting the first two add instruction, let gcc select
register for me and tell me which register it selected. so i can make my
own binary code using .long instruction. But i do not want to modify the
gcc compiler to let it understand my instruction.
Thank you for your help
jie zhou wrote: > what i want is deleting the first two add instruction, let gcc select > register for me and tell me which register it selected. so i can make my > own binary code using .long instruction. But i do not want to modify the > gcc compiler to let it understand my instruction. There are several approaches: (A) You don't need to change GCC. It's sufficient to teach binutils the new instructions/instruction formats with the additinal benefit that you will see the new instructions in disassembly. (B) Drag the arithmetic from C-level to (inline) assembly. You will need an output modifier to print a GPR as it's number. If your GCC port does not have it yet: add it. It's TARGET_PRINT_OPERAND hook in your ./gcc/config/target/target.c, see GCC's internals documentation.
Johann L. thank you very much for your help > You don't need to change GCC. It's sufficient to teach binutils the > new instructions/instruction formats with the additinal benefit that > you will see the new instructions in disassembly. i prefer to teaching gnu binutils the new instructions. in fact, i use microblaze gnu tools to compile my code. but how to teach gnu binutils? can you say some details?
You can find a draft at http://sourceware.org/binutils/binutils-porting-guide.txt Look at your backend and other ports to learn more.