From d9a14daa00e62de637c063f357c38cd86efd7666 Mon Sep 17 00:00:00 2001 From: johannst Date: Sat, 30 Apr 2022 17:43:08 +0000 Subject: deploy: f33fbacc6aaa54599458ac3eb375708650656010 --- arch/riscv.html | 292 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 292 insertions(+) create mode 100644 arch/riscv.html (limited to 'arch/riscv.html') diff --git a/arch/riscv.html b/arch/riscv.html new file mode 100644 index 0000000..2e5f697 --- /dev/null +++ b/arch/riscv.html @@ -0,0 +1,292 @@ + + + + + + riscv - Notes + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
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+

riscv

+

keywords: rv32, rv64

+
    +
  • ISA type: RISC
    • +
  • Endianness: little, big
    • +
+

Registers

+
    +
  • riscv32 => XLEN=32
    • +
  • riscv64 => XLEN=64
    • +
+

General purpose registers

+
[XLEN-1:0]     abi name     desc
+---------------------------------------------
+x0             zero         zero register
+x1             ra           return addr
+x2             sp           stack ptr
+x3             gp           global ptr
+x4             tp           thread ptr
+x5-x7          t0-t2        temp regs
+x8-x9          s0-s1        saved regs
+x10-x17        a0-a7        arg regs
+x18-x27        s2-s11       saved regs
+x28-x31        t3-t6        temp regs
+
+

ASM skeleton

+

Small assembler skeleton, ready to use with following properties:

+
    +
  • use raw Linux syscalls (man 2 syscall for ABI)
    • +
  • no C runtime (crt)
    • +
  • gnu assembler gas
    • +
+
// file: greet.S
+
+#include <asm/unistd.h>     // syscall NRs
+
+    .section .text, "ax", @progbits
+    .balign 4               // align code on 4byte boundary
+    .global _start
+_start:
+    li a0, 2                // fd
+    la a1, greeting         // buf
+    ld a2, (greeting_len)   // &len
+    li a7, __NR_write       // write(2) syscall
+    ecall
+
+    li a0, 42               // exit code
+    li a7, __NR_exit        // exit(2) syscall
+    ecall
+
+    .balign 8               // align data on 8byte boundary
+    .section .rodata, "a", @progbits
+greeting:
+    .asciz "Hi ASM-World!\n"
+greeting_len:
+    .int .-greeting
+
+
+

man gcc: file.S assembler code that must be preprocessed.

+
+

To cross-compile and run:

+
> riscv64-linux-gnu-gcc -o greet greet.S -nostartfiles -nostdlib                \
+    -Wl,--dynamic-linker=/usr/riscv64-linux-gnu/lib/ld-linux-riscv64-lp64d.so.1 \
+  && qemu-riscv64 ./greet
+Hi ASM-World!
+
+
+

Cross-compiling on Ubuntu 20.04 (x86_64), paths might differ on other +distributions. Explicitly specifying the dynamic linker should not be +required when compiling natively on riscv.

+

Select dynamic linker according to abi used during compile & link.

+
+

References

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