Help me correct this asm please

I rarely use assembly so I ended up getting this wrong somehow, would also like to just dump all registers into the 'dst' parameter, as for the reason I made this, had an idea to use executed instruction count for pseudo random numbers and the BIOS RTC will be my fallback option, I haven't found any instructions providing an instruction execution count as yet however so I welcome help in that regard too.

Code:

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#include <inttypes.h>
#include <string.h>
typedef intmax_t asm_registers_t[0x10];

inline void bios(
        asm_registers_t *dst,
        unsigned char interrupt, unsigned char ah, unsigned char al )
{
        (void)memset( dst, 0, sizeof(asm_registers_t) );
        asm( "mov %ah,%1", ah );
        asm( "mov %al,%1", al );
        asm( "int %1", interrupt );
}

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Been looking into the syntax of asm now that gospel is over and got as far as this:

Code:

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#include <inttypes.h>
#include <string.h>

typedef unsigned int uint;
typedef unsigned char uchar;
typedef unsigned short ushort;
typedef intmax_t asm_registers_t[0x10];

volatile void bios(
        asm_registers_t *dst,
        uchar interrupt,
        uchar ah,
        uchar al
);
...
#include "bios.h"
#include <stdio.h>

int main() {
#if 0
        printf( "%s\n", PRIxMAX );
#else
        unsigned int i = 0;
        asm_registers_t reg = {0};
        bios(&reg,1u,0u,0u);
        for ( i = 0; i < 0x10; ++i ) {
                (void)printf(
                        "reg[%u] = %" PRIxMAX "\n",
                        i, reg[i]
                );
        }
#endif
}

int hex2CHAR( int val )
{
        val &= 0xF;
        if ( val < 10 )
                return '0' + val;
        return 'A' + val;
}

int hex2char( int val )
{
        val &= 0xF;
        if ( val < 10 )
                return '0' + val;
        return 'a' + val;
}

volatile void bios(
        asm_registers_t *dst,
        uchar interrupt,
        uchar ah,
        uchar al
)
{
        volatile ushort *word = (ushort*)(&word);
        (void)memset( dst, 0, sizeof(asm_registers_t) );
        fprintf( stderr, "word = %p, %hx", word, *word );
        for ( ; *word != 0xCD00; ++word );
        ++word; *word = 0xCD00 | (uchar)interrupt;
        asm( "mov ah,%0" : "=r" (ah) );
        asm( "mov al,%0" : "=r" (al) );
        asm( "int 0x00" );
#if 0
        asm( "mov %0,%r0" : "=m" ((*dst)[0]) );
        asm( "mov %0,%r1" : "=m" ((*dst)[1]) );
        asm( "mov %0,%r2" : "=m" ((*dst)[2]) );
        asm( "mov %0,%r3" : "=m" ((*dst)[3]) );
        asm( "mov %0,%r4" : "=m" ((*dst)[4]) );
        asm( "mov %0,%r5" : "=m" ((*dst)[5]) );
        asm( "mov %0,%r6" : "=m" ((*dst)[6]) );
        asm( "mov %0,%r7" : "=m" ((*dst)[7]) );
        asm( "mov %0,%r8" : "=m" ((*dst)[8]) );
        asm( "mov %0,%r9" : "=m" ((*dst)[9]) );
        asm( "mov %0,%r10" : "=m" ((*dst)[10]) );
        asm( "mov %0,%r11" : "=m" ((*dst)[11]) );
        asm( "mov %0,%r12" : "=m" ((*dst)[12]) );
        asm( "mov %0,%r13" : "=m" ((*dst)[13]) );
        asm( "mov %0,%r14" : "=m" ((*dst)[14]) );
        asm( "mov %0,%r15" : "=m" ((*dst)[15]) );
#endif
        *word = 0xCD00;
}

---

But still no luck in getting it to compile

Edit: Forgot to mention the compiler error message:

Code:

---

bios.c:50: Error: operand size mismatch for `int'

---

Also forgot to add some details to those mov functions that copy all the registers, added but they still give me errors:

Code:

---

gcc -Wall -o bios bios.c -lpthread && ./bios
bios.c: In function ‘bios’:
bios.c:52:2: error: invalid 'asm': operand is not a specific integer, invalid operand code 'r'
  52 |  asm( "mov %0,%r0" : "=m" ((*dst)[0]) );
      |  ^~~
bios.c:53:2: error: invalid 'asm': operand number out of range
  53 |  asm( "mov %0,%r1" : "=m" ((*dst)[1]) );
      |  ^~~
bios.c:54:2: error: invalid 'asm': operand number out of range
  54 |  asm( "mov %0,%r2" : "=m" ((*dst)[2]) );
      |  ^~~
bios.c:55:2: error: invalid 'asm': operand number out of range
  55 |  asm( "mov %0,%r3" : "=m" ((*dst)[3]) );
      |  ^~~
bios.c:56:2: error: invalid 'asm': operand number out of range
  56 |  asm( "mov %0,%r4" : "=m" ((*dst)[4]) );
      |  ^~~
bios.c:57:2: error: invalid 'asm': operand number out of range
  57 |  asm( "mov %0,%r5" : "=m" ((*dst)[5]) );
      |  ^~~
bios.c:58:2: error: invalid 'asm': operand number out of range
  58 |  asm( "mov %0,%r6" : "=m" ((*dst)[6]) );
      |  ^~~
bios.c:59:2: error: invalid 'asm': operand number out of range
  59 |  asm( "mov %0,%r7" : "=m" ((*dst)[7]) );
      |  ^~~
bios.c:60:2: error: invalid 'asm': operand number out of range
  60 |  asm( "mov %0,%r8" : "=m" ((*dst)[8]) );
      |  ^~~
bios.c:61:2: error: invalid 'asm': operand number out of range
  61 |  asm( "mov %0,%r9" : "=m" ((*dst)[9]) );
      |  ^~~
bios.c:62:2: error: invalid 'asm': operand number out of range
  62 |  asm( "mov %0,%r10" : "=m" ((*dst)[10]) );
      |  ^~~
bios.c:63:2: error: invalid 'asm': operand number out of range
  63 |  asm( "mov %0,%r11" : "=m" ((*dst)[11]) );
      |  ^~~
bios.c:64:2: error: invalid 'asm': operand number out of range
  64 |  asm( "mov %0,%r12" : "=m" ((*dst)[12]) );
      |  ^~~
bios.c:65:2: error: invalid 'asm': operand number out of range
  65 |  asm( "mov %0,%r13" : "=m" ((*dst)[13]) );
      |  ^~~
bios.c:66:2: error: invalid 'asm': operand number out of range
  66 |  asm( "mov %0,%r14" : "=m" ((*dst)[14]) );
      |  ^~~
bios.c:67:2: error: invalid 'asm': operand number out of range
  67 |  asm( "mov %0,%r15" : "=m" ((*dst)[15]) );
      |  ^~~
Compilation failed.

---

Well I managed to fix most of the errors, the one that remains is that size mismatch which I have no idea how to fix since I don't even know what the problem is

Code:

---

int set_page_perm( void * addr, int perm )
{
        size_t size = sysconf( _SC_PAGE_SIZE );
        addr -= ((uintptr_t)addr % size);
        return mprotect( addr, size, perm );
}

volatile int bios(
        asm_registers_t *dst,
        uchar interrupt,
        uchar ah,
        uchar al
)
{
        int perm = PROT_READ | PROT_EXEC;
        if ( set_page_perm( bios, perm | PROT_WRITE ) == -1 )
                return -1;
        volatile ushort *word = (ushort*)(&word);
        (void)memset( dst, 0, sizeof(asm_registers_t) );
        fprintf( stderr, "word = %p, %hx", word, *word );
        for ( ; *word != 0xCD00; ++word );
        ++word; *word = 0xCD00 | (uchar)interrupt;
        asm( "mov %%ah,%0" : : "r" (ah) : "ah" );
        asm( "mov %%al,%0" : : "r" (al) : "al" );
        asm( "int 0x00" );
        asm( "mov %0,%%rax" : "=m" ((*dst)[0]) );
        asm( "mov %0,%%rcx" : "=m" ((*dst)[1]) );
        asm( "mov %0,%%rdx" : "=m" ((*dst)[2]) );
        asm( "mov %0,%%rbx" : "=m" ((*dst)[3]) );
        asm( "mov %0,%%rsp" : "=m" ((*dst)[4]) );
        asm( "mov %0,%%rbp" : "=m" ((*dst)[5]) );
        asm( "mov %0,%%rsi" : "=m" ((*dst)[6]) );
        asm( "mov %0,%%rdi" : "=m" ((*dst)[7]) );
        asm( "mov %0,%%r8" : "=m" ((*dst)[8]) );
        asm( "mov %0,%%r9" : "=m" ((*dst)[9]) );
        asm( "mov %0,%%r10" : "=m" ((*dst)[10]) );
        asm( "mov %0,%%r11" : "=m" ((*dst)[11]) );
        asm( "mov %0,%%r12" : "=m" ((*dst)[12]) );
        asm( "mov %0,%%r13" : "=m" ((*dst)[13]) );
        asm( "mov %0,%%r14" : "=m" ((*dst)[14]) );
        asm( "mov %0,%%r15" : "=m" ((*dst)[15]) );
        *word = 0xCD00;
        return set_page_perm( bios, perm );
}

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I think I fixed the error, either way I haven't been able to change the interrupt yet, on another note I tried adding in another register I learned off only for the compiler to say MOV doesn't support that so I tried a work around of XOR, OR then MOV but the compiler is also complaining there, any help would be appreciated.

Code:

---

int bios( asm_registers_t *dst, uchar interrupt, uchar ah, uchar al )
{
        int ret = -1;
        int perm = PROT_READ | PROT_EXEC;
        ushort *word = (ushort*)bios;
       
        if ( set_page_perm( bios, perm | PROT_WRITE ) == -1 )
                goto fail;
       
        (void)memset( dst, 0, sizeof(asm_registers_t) );
        (void)fprintf( stderr, "ptr  = %p\n", dst );
       
#if 0
        print_word( word );
        asm( "mov %0,%%rbp" : "=m" (*word) );
#endif

        for ( ; *word != 0xCD09; ++word )
        {
                print_word( word );
        }
       
        ++word;
        if ( *((uchar*)word) != 0xCD )
        {
                fprintf( stderr, "Failed to find 0xCD # (aka int #)\n" );
                return -1;
        }
       
        *((ushort*)word) = 0xCD | ((ushort)interrupt << CHAR_BIT);
       
        asm( "mov %%ah,%0" : : "r" (ah) : "ah" );
        asm( "mov %%al,%0" : : "r" (al) : "al" );
        asm( "nop" );
        asm( "nop" );
        asm( "nop" );
        asm( "nop" );
        asm( "nop" );
        asm( "nop" );
        asm( "nop" );
        asm( "nop" );
        asm( "int $0x00" : : : "cc", "memory" );
        ret = 0;
        fail:
        asm( "mov %0,%%rax" : "=m" ((*dst)[REG_RAX]) );
        asm( "mov %0,%%rcx" : "=m" ((*dst)[REG_RCX]) );
        asm( "mov %0,%%rdx" : "=m" ((*dst)[REG_RDX]) );
        asm( "mov %0,%%rbx" : "=m" ((*dst)[REG_RBX]) );
        asm( "mov %0,%%rsp" : "=m" ((*dst)[REG_RSP]) );
        asm( "mov %0,%%rbp" : "=m" ((*dst)[REG_RBP]) );
        asm( "mov %0,%%rsi" : "=m" ((*dst)[REG_RSI]) );
        asm( "mov %0,%%rdi" : "=m" ((*dst)[REG_RDI]) );
        asm( "mov %0,%%r8" : "=m" ((*dst)[REG_R08]) );
        asm( "mov %0,%%r9" : "=m" ((*dst)[REG_R09]) );
        asm( "mov %0,%%r10" : "=m" ((*dst)[REG_R10]) );
        asm( "mov %0,%%r11" : "=m" ((*dst)[REG_R11]) );
        asm( "mov %0,%%r12" : "=m" ((*dst)[REG_R12]) );
        asm( "mov %0,%%r13" : "=m" ((*dst)[REG_R13]) );
        asm( "mov %0,%%r14" : "=m" ((*dst)[REG_R14]) );
        asm( "mov %0,%%r15" : "=m" ((*dst)[REG_R15]) );
        asm( "xor %%rax,%%rax" : : : "rax" );
        asm( "or %%rax,%%rip" : : : "rax" );
        asm( "mov %0,%%rax"        : "=m" ((*dst)[REG_RIP]) );
       
        return (ret == 0) ? set_page_perm( bios, perm ) : ret;
}

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Edit: Oops, forgot to add the error message:

Code:

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bios.c:114: Error: operand type mismatch for `or'

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