x86 64 - x86_64 assembly %rsp vs %esp -

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i have been playing assembly recently, , came across strange bug in program. have found if modify %rsp doing 64-bit math, works fine, if modify %esp same amount, except 32-bit math, segmentation fault. tried printing out both %esp , %rsp, , same every time run.

question: why matter whether 64-bit math or 32-bit math when whole register using 32 bits?

.cstring     _format: .asciz "%d\n"  .text .globl _main _main:     # program setup     pushq   %rbp     movq    %rsp, %rbp      # program - 16 byte aligned @ point     # print stack pointer memory     movq    %rsp, %rax     call    bob            # prints same value next call bob     xorq    %rax, %rax     movl    %esp, %eax     call    bob            # prints same value previous call bob      # code breaks     subl    $16, %esp      # bug here if use (32 bit math)     subq    $16, %rsp      # works fine if use (64 bit math)     call    bob     addq    $16, %rsp      # program cleanup     movq    %rbp, %rsp     popq    %rbp     ret  # assumes 16 byte aligned when called. prints %rax  bob:     subq    $8, %rsp     movq    %rax, %rsi     lea     _format(%rip), %rdi     call    _printf     addq    $8, %rsp     ret

in x86_64, addresses 64 bits, how can expect 32-bit math on , still working fine? 32-bit operations on x86_64 0 out top 32 bits, render address invalid


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