Double jump when calling functions

Question

I wanted to ask why there is a double jump when calling some functions? For example first call:

.text:005AC266                 push    eax
.text:005AC267                 call    j_WinRegisterWindow

Second jump:

.text:00491157 j_WinRegisterWindow proc near           ; CODE XREF: WinMain+37p
.text:00491157                 jmp     WinRegisterWindow
.text:00491157 j_WinRegisterWindow endp

And finally it's function:

.text:005AC180 ; int __cdecl WinRegisterWindow(HINSTANCE hInstance)
.text:005AC180 WinRegisterWindow proc near             ; CODE XREF: j_WinRegisterWindowj
.text:005AC180
.text:005AC180 hInstance       = dword ptr  8
.text:005AC180
.text:005AC180                 push    ebp
.text:005AC181                 mov     ebp, esp
.text:005AC183                 sub     esp, 40h
.text:005AC186                 push    ebx
.text:005AC187                 push    esi
.text:005AC188                 push    edi

Answer 1

It because of the "Link Incrementally".

For example, there is a test program:

#include <iostream>

void test(void)
{
    std::cout << "Hello" << std::endl;
    return;
}

int main()
{
    test();
    return 0;
}

If I enable /INCREMENTAL option, the code is:

; __int64 __fastcall main()
main proc near
push    rbp
push    rdi
sub     rsp, 0E8h
lea     rbp, [rsp+20h]
lea     rcx, __2B9C3776_ConsoleApplication1@cpp ; JMC_flag
call    j___CheckForDebuggerJustMyCode
call    j_?test@@YAXXZ  ; test(void)
xor     eax, eax
lea     rsp, [rbp+0C8h]
pop     rdi
pop     rbp
retn
main endp

; void test(void)
j_?test@@YAXXZ proc near
jmp     ?test@@YAXXZ    ; test(void)
j_?test@@YAXXZ endp

; void test(void)
?test@@YAXXZ proc near
push    rbp
push    rdi
sub     rsp, 0E8h
lea     rbp, [rsp+20h]
lea     rcx, __2B9C3776_ConsoleApplication1@cpp ; JMC_flag
call    j___CheckForDebuggerJustMyCode
lea     rdx, _Val       ; "Hello"
mov     rcx, cs:__imp_?cout@std@@3V?$basic_ostream@DU?$char_traits@D@std@@@1@A ; _Ostr
call    j_??$?6U?$char_traits@D@std@@@std@@YAAEAV?$basic_ostream@DU?$char_traits@D@std@@@0@AEAV10@PEBD@Z ; std::operator<<<std::char_traits<char>>(std::ostream &,char const *)
lea     rdx, j_??$endl@DU?$char_traits@D@std@@@std@@YAAEAV?$basic_ostream@DU?$char_traits@D@std@@@0@AEAV10@@Z ; std::endl<char,std::char_traits<char>>(std::ostream &)
mov     rcx, rax
call    cs:__imp_??6?$basic_ostream@DU?$char_traits@D@std@@@std@@QEAAAEAV01@P6AAEAV01@AEAV01@@Z@Z ; std::ostream::operator<<(std::ostream & (*)(std::ostream &))
lea     rsp, [rbp+0C8h]
pop     rdi
pop     rbp
retn
?test@@YAXXZ endp

And if I disable the /INCREMENTAL option, the code is:

; __int64 __fastcall main()
main proc near
push    rbp
push    rdi
sub     rsp, 0E8h
lea     rbp, [rsp+20h]
lea     rcx, __2B9C3776_ConsoleApplication1@cpp ; JMC_flag
call    __CheckForDebuggerJustMyCode
call    ?test@@YAXXZ    ; test(void)
xor     eax, eax
lea     rsp, [rbp+0C8h]
pop     rdi
pop     rbp
retn
main endp

; void test(void)
?test@@YAXXZ proc near
push    rbp
push    rdi
sub     rsp, 0E8h
lea     rbp, [rsp+20h]
lea     rcx, __2B9C3776_ConsoleApplication1@cpp ; JMC_flag
call    __CheckForDebuggerJustMyCode
lea     rdx, _Val       ; "Hello"
mov     rcx, cs:__imp_?cout@std@@3V?$basic_ostream@DU?$char_traits@D@std@@@1@A ; _Ostr
call    ??$?6U?$char_traits@D@std@@@std@@YAAEAV?$basic_ostream@DU?$char_traits@D@std@@@0@AEAV10@PEBD@Z ; std::operator<<<std::char_traits<char>>(std::ostream &,char const *)
lea     rdx, ??$endl@DU?$char_traits@D@std@@@std@@YAAEAV?$basic_ostream@DU?$char_traits@D@std@@@0@AEAV10@@Z ; std::endl<char,std::char_traits<char>>(std::ostream &)
mov     rcx, rax
call    cs:__imp_??6?$basic_ostream@DU?$char_traits@D@std@@@std@@QEAAAEAV01@P6AAEAV01@AEAV01@@Z@Z ; std::ostream::operator<<(std::ostream & (*)(std::ostream &))
lea     rsp, [rbp+0C8h]
pop     rdi
pop     rbp
retn
?test@@YAXXZ endp

More info about the Link Incrementally: https://docs.microsoft.com/en-us/cpp/build/reference/incremental-link-incrementally?view=msvc-170