make a function on the fly to simulate closures

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@near glade

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[delicate marlin]

Oh, the post is gone.
@near glade, if you're still interested, have a look at https://www.gnu.org/software/libffcall/callback.html

[near glade]

i eventually got it to work, i think

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>
#include <sys/mman.h>

#define i32 int32_t
#define u64 uint64_t 
#define u8 uint8_t 

typedef i32(*closure)(void *, i32);
typedef i32(*total)(i32);

total from_closure(closure f, void *state) {
    u64 f_adr = (u64)f;
    u64 state_adr = (u64)state;
    u8 code[] = {
        0x48, 0xb8, f_adr & 0xFF,(f_adr >> 8) & 0xFF,(f_adr >> 16) & 0xFF,(f_adr >> 24) & 0xFF,(f_adr >> 32) & 0xFF,(f_adr >> 40) & 0xFF,(f_adr >> 48) & 0xFF,(f_adr >> 56) & 0xFF, // movabs rax, closure adress
        0x89, 0xfe, // mov esi, edi
        0x48, 0xbf, state_adr & 0xFF,(state_adr >> 8) & 0xFF,(state_adr >> 16) & 0xFF,(state_adr >> 24) & 0xFF,(state_adr >> 32) & 0xFF,(state_adr >> 40) & 0xFF,(state_adr >> 48) & 0xFF,(state_adr >> 56) & 0xFF, // movabs rdi, state
        0xff, 0xe0, // jmp rax
    };
    total funptr = mmap(NULL, sizeof(code), PROT_WRITE | PROT_EXEC, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
    memcpy(funptr, code, sizeof(code));
    return funptr;
}

i32 closure_example(void *state, i32 y) {
    return (*(int*)state)*y;
}

i32 main() {
    i32 *state = malloc(sizeof(i32));
    *state = 42;
    total test = from_closure(&closure_example, state);
    printf("%d\n", test(2));
}

i was interested in making it myself, but yeah, for a practical usecase that libffcall/callback seems useful