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| en:multiasm:exercisebook:pc:sut:scenarios_standalone [2026/05/20 15:17] – [Implementation of calculation functions] ktokarz | en:multiasm:exercisebook:pc:sut:scenarios_standalone [2026/05/20 15:57] (current) – [Implementation of calculation functions] ktokarz | ||
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| The caller passes arguments according to the Windows x64 ABI. First four arguments through RCX, RDX, R8 and R9 registers. Further arguments are placed onto the stack. The caller is also responsible for reserving the shadow space for all arguments before the call, even those passed through registers. That's why 32 bytes are reserved before the return address is automatically placed on the stack by the call instruction. | The caller passes arguments according to the Windows x64 ABI. First four arguments through RCX, RDX, R8 and R9 registers. Further arguments are placed onto the stack. The caller is also responsible for reserving the shadow space for all arguments before the call, even those passed through registers. That's why 32 bytes are reserved before the return address is automatically placed on the stack by the call instruction. | ||
| - | Please note the order of arguments. It is assumed that they are placed onto the stack in reverse order. The last argument is placed on the stack first. That's why the 6th argument is at the higher address, next is the 5th argument and next there is a shadow space for arguments 1 - 4. From the perspective of a function, the first argument (or rather its shadow) is just after the return address. As the return address consumes 8 bytes, the first argument is at address SP+8. | + | Please note the order of arguments. It is assumed that they are placed onto the stack in reverse order. The last argument is placed on the stack first. That's why the 6th argument is at the higher address, next is the 5th argument and next there is a shadow space for arguments 1 - 4. From the perspective of a function, the first argument (or rather its shadow) is just after the return address. As the return address consumes 8 bytes, |
| + | |||
| + | How to call such a function? Putting the first four parameters into registers is quite simple. To place remaining arguments onto the stack, it is possible to use the **push** instruction. | ||
| + | <code asm> | ||
| + | ;call sum of 6 integers function | ||
| + | |||
| + | mov rcx, 1 ; 1st argmument | ||
| + | mov rdx, 2 ; 2nd argmument | ||
| + | mov r8, 3 ; 3rd argmument | ||
| + | mov r9, 4 ; 4th argmument | ||
| + | mov r11, 6 | ||
| + | push r11 ; 6th argument | ||
| + | mov r10, 5 | ||
| + | push r10 ; 5th argument | ||
| + | |||
| + | sub rsp, 20h ; 32 bytes of the shadow space | ||
| + | |||
| + | call sum_6_int ; function call | ||
| + | |||
| + | add rsp, 30h ; stack cleanup | ||
| + | mov rcx, rax ; result in rax | ||
| + | </ | ||
| + | |||
| + | The figure {{ref> | ||
| + | <figure ex_stack_caller_push> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
