On Thu, Sep 25, 2025 at 2:50 PM Jan Mercl <[email protected]> wrote:
> Is it possible to write code in Go ABI0 assembler that implements a jump
> table?
For posterity, this proof of concept seems to work:
jnml@e5-1650:~/tmp/jumptable$ cat main.go
package main
// int switch_func(int op) {
// int result;
// switch (op) {
// case 0:
// result = 100;
// break;
// case 1:
// result = 200;
// break;
// case 2:
// result = 300;
// break;
// default:
// result = -1;
// break;
// }
// return result;
// }
func switch_func(op int64) int64
func main() {
for i := int64(0); i < 4; i++ {
println(i, switch_func(i))
}
}
jnml@e5-1650:~/tmp/jumptable$ cat main.s
#include "funcdata.h"
#include "textflag.h"
TEXT ·switch_func(SB), $0-16
GO_ARGS
NO_LOCAL_POINTERS
JMP over
JMP case0
JMP case1
JMP case2
over:
MOVQ op+0(FP), AX
CMPQ AX, $2
JA dflt
LEAQ ·switch_func+2(SB), CX
ADDQ AX, AX
ADDQ AX, CX
JMP CX
case0:
MOVQ $100, AX
JMP done
case1:
MOVQ $200, AX
JMP done
case2:
MOVQ $300, AX
JMP done
dflt:
MOVQ $-1, AX
done:
MOVQ AX, ret+8(FP)
RET
jnml@e5-1650:~/tmp/jumptable$ go run .
0 100
1 200
2 300
3 -1
jnml@e5-1650:~/tmp/jumptable$
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