jmp_table.cpp

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/*
    sample of move(reg, LABEL);, L(LABEL), putL(LABEL);
*/
#include <stdio.h>
#define XBYAK_NO_OP_NAMES
#include <xbyak/xbyak.h>
 
const int expectTbl[] = {
    5, 9, 12
};
 
struct Code : Xbyak::CodeGenerator {
    explicit Code(int mode, size_t size, void *p)
        : Xbyak::CodeGenerator(size, p)
    {
        inLocalLabel();
#ifdef XBYAK64
        const Xbyak::Reg64& a = rax;
        const Xbyak::Reg64& c = rcx;
#ifdef XBYAK64_WIN
        mov(rax, rcx);
#else
        mov(rax, rdi);
#endif
#else
        const Xbyak::Reg32& a = eax;
        const Xbyak::Reg32& c = ecx;
        mov(a, ptr [esp + 4]);
#endif
 
        switch (mode) {
        case 0:
            mov(c, ".jmp_table");
            lea(c, ptr [c + a * 8]);
            jmp(c);
        align(8);
            L(".jmp_table");
            mov(a, expectTbl[0]);
            ret();
        align(8);
            mov(a, expectTbl[1]);
            ret();
        align(8);
            mov(a, expectTbl[2]);
            ret();
            break;
 
        case 1:
            /*
                the label for putL is defined when called
            */
            mov(c, ".jmp_table");
            jmp(ptr [c + a * (int)sizeof(size_t)]);
        L(".label1");
            mov(a, expectTbl[0]);
            jmp(".end");
        L(".label2");
            mov(a, expectTbl[1]);
            jmp(".end");
        L(".label3");
            mov(a, expectTbl[2]);
            jmp(".end");
        L(".end");
            ret();
            ud2();
 
            align(8);
        L(".jmp_table");
        putL(".label1");
        putL(".label2");
        putL(".label3");
            break;
 
        case 2:
            /*
                the label for putL is not defined when called
            */
            jmp(".in");
            ud2();
            align(8);
        L(".jmp_table");
        putL(".label1");
        putL(".label2");
        putL(".label3");
        L(".in");
            mov(c, ".jmp_table");
            jmp(ptr [c + a * (int)sizeof(size_t)]);
        L(".label1");
            mov(a, expectTbl[0]);
            jmp(".end");
        L(".label2");
            mov(a, expectTbl[1]);
            jmp(".end");
        L(".label3");
            mov(a, expectTbl[2]);
            jmp(".end");
        L(".end");
            ret();
            break;
        }
        outLocalLabel();
    }
};
 
int main()
    try
{
    for (int mode = 0; mode < 3; mode++) {
        printf("mode=%d\n", mode);
        for (int grow = 0; grow < 2; grow++) {
            printf("auto grow=%s\n", grow ? "on" : "off");
            Code c(mode, grow ? 30 : 4096, grow ? Xbyak::AutoGrow : 0);
            int (*f)(int) = c.getCode<int (*)(int)>();
            c.ready();
            for (int i = 0; i < 3; i++) {
                const int a = expectTbl[i];
                const int b = f(i);
                if (a != b) {
                    printf("ERR i=%d, a=%d, b=%d\n", i, a, b);
                    exit(1);
                }
            }
        }
    }
    puts("ok");
} catch (std::exception& e) {
    printf("ERR %s\n", e.what());
}