#include<iostream>

using namespace std;

int main()
{
    
    char arr[40960];

    for(auto i =0;i<40960;++i)
        arr[i]='c';

    std::cout<<sizeof(arr)<<std::endl;

    return 0;
}
       

we’re taught local variables allocate in stack ,so we can’t take up too many byte of stack , but in this case program doesnt crash, does anyone know what magic compiler does?

gcc –version
gcc (GCC) 14.1.1 20240522
Copyright (C) 2024 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

disassemble code:

0000000000001159 <main>:
    1159:   55                      push   %rbp
    115a:   48 89 e5                mov    %rsp,%rbp
    115d:   48 81 ec 20 a0 00 00    sub    $0xa020,%rsp
    1164:   64 48 8b 04 25 28 00    mov    %fs:0x28,%rax
    116b:   00 00 
    116d:   48 89 45 f8             mov    %rax,-0x8(%rbp)
    1171:   31 c0                   xor    %eax,%eax
    1173:   c7 85 ec 5f ff ff 00    movl   $0x0,-0xa014(%rbp)
    117a:   00 00 00 
    117d:   eb 17                   jmp    1196 <main+0x3d>
    117f:   8b 85 ec 5f ff ff       mov    -0xa014(%rbp),%eax
    1185:   48 98                   cltq
    1187:   c6 84 05 f0 5f ff ff    movb   $0x63,-0xa010(%rbp,%rax,1)
    118e:   63 
    118f:   83 85 ec 5f ff ff 01    addl   $0x1,-0xa014(%rbp)
    1196:   81 bd ec 5f ff ff ff    cmpl   $0x9fff,-0xa014(%rbp)
    119d:   9f 00 00 
    11a0:   7e dd                   jle    117f <main+0x26>
    11a2:   be 00 a0 00 00          mov    $0xa000,%esi
    11a7:   48 8d 05 92 2e 00 00    lea    0x2e92(%rip),%rax        # 4040 <_ZSt4cout@GLIBCXX_3.4>
    11ae:   48 89 c7                mov    %rax,%rdi
    11b1:   e8 7a fe ff ff          call   1030 <_ZNSolsEm@plt>
    11b6:   48 8b 15 03 2e 00 00    mov    0x2e03(%rip),%rdx        # 3fc0 <_ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_@GLIBCXX_3.4>
    11bd:   48 89 d6                mov    %rdx,%rsi
    11c0:   48 89 c7                mov    %rax,%rdi
    11c3:   e8 78 fe ff ff          call   1040 <_ZNSolsEPFRSoS_E@plt>
    11c8:   b8 00 00 00 00          mov    $0x0,%eax
    11cd:   48 8b 55 f8             mov    -0x8(%rbp),%rdx
    11d1:   64 48 2b 14 25 28 00    sub    %fs:0x28,%rdx
    11d8:   00 00 
    11da:   74 05                   je     11e1 <main+0x88>
    11dc:   e8 6f fe ff ff          call   1050 <__stack_chk_fail@plt>
    11e1:   c9                      leave
    11e2:   c3                      ret

sorry for my bad english