To learn assembly I am viewing the assembly generated by GCC using the -S command for some simple c programs. I have an add function which accepts some ints and some char and adds them together. I am just wondering why the char parameters are pushed onto the stack as 8 bytes (pushq)? Why not just push a single byte?

    .file   "test.c"
    .text
    .globl  add
    .type   add, @function
add:
.LFB0:
    .cfi_startproc
    pushq   %rbp
    .cfi_def_cfa_offset 16
    .cfi_offset 6, -16
    movq    %rsp, %rbp
    .cfi_def_cfa_register 6
    movl    %edi, -4(%rbp)
    movl    %esi, -8(%rbp)
    movl    %edx, -12(%rbp)
    movl    %ecx, -16(%rbp)
    movl    %r8d, -20(%rbp)
    movl    %r9d, -24(%rbp)
    movl    16(%rbp), %ecx
    movl    24(%rbp), %edx
    movl    32(%rbp), %eax
    movb    %cl, -28(%rbp)
    movb    %dl, -32(%rbp)
    movb    %al, -36(%rbp)
    movl    -4(%rbp), %edx
    movl    -8(%rbp), %eax
    addl    %eax, %edx
    movl    -12(%rbp), %eax
    addl    %eax, %edx
    movl    -16(%rbp), %eax
    addl    %eax, %edx
    movl    -20(%rbp), %eax
    addl    %eax, %edx
    movl    -24(%rbp), %eax
    addl    %eax, %edx
    movsbl  -28(%rbp), %eax
    addl    %eax, %edx
    movsbl  -32(%rbp), %eax
    addl    %eax, %edx
    movsbl  -36(%rbp), %eax
    addl    %edx, %eax
    popq    %rbp
    .cfi_def_cfa 7, 8
    ret
    .cfi_endproc
.LFE0:
    .size   add, .-add
    .globl  main
    .type   main, @function
main:
.LFB1:
    .cfi_startproc
    pushq   %rbp
    .cfi_def_cfa_offset 16
    .cfi_offset 6, -16
    movq    %rsp, %rbp
    .cfi_def_cfa_register 6
    pushq   $9
    pushq   $8
    pushq   $7
    movl    $6, %r9d
    movl    $5, %r8d
    movl    $4, %ecx
    movl    $3, %edx
    movl    $2, %esi
    movl    $1, %edi
    call    add
    addq    $24, %rsp
    leave
    .cfi_def_cfa 7, 8
    ret
    .cfi_endproc
.LFE1:
    .size   main, .-main
    .ident  "GCC: (Ubuntu 4.9.2-10ubuntu13) 4.9.2"
    .section    .note.GNU-stack,"",@progbits

#include <stdio.h>

int add(int a, int b, int c, int d, int e, int f, char g, char h, char i)
{
    return a + b + c + d + e + f + g + h + i;
}

int main()
{
    return add(1, 2, 3, 4, 5, 6, 7, 8, 9);
}