#include <stdio.h>
int main(int argc, char* argv[]) {
int n, svar;
printf("Please enter an integer: ");
while (scanf("%d",&svar)!=123) {
//asm ("int $3"); // see switch under the hood
if (svar==12) asm ("int $3");
switch (svar)
{
case 12:
printf("That was case 12\n");
case 24:
printf("That was case 24\n");
case 16:
printf("That was case 16\n");
break;
case 14:
printf("That was case 14\n");
default:
printf("That was default\n");
}
}
}
Compiled with GCC:
0040267F |. 8B4424 1C |mov eax, [local.2] ; svar
00402683 |> 83F8 0E |cmp eax, 0E
00402686 |. 74 3B |je short 004026C3
00402688 |. 7E 26 |jle short 004026B0
0040268A |. 83F8 10 |cmp eax, 10
0040268D |. 74 11 |je short 004026A0
0040268F |. 83F8 18 |cmp eax, 18
00402692 |. 75 3B |jne short 004026CF
00402694 |> C70424 724040 |mov dword ptr [local.9], offset 0040407 ; /string => "That was case 24"
0040269B |. E8 D4FEFFFF |call <jmp.&msvcrt.puts> ; \MSVCRT.puts
004026A0 |> C70424 834040 |mov dword ptr [local.9], offset 0040408 ; /string => "That was case 16"
004026A7 |. E8 C8FEFFFF |call <jmp.&msvcrt.puts> ; \MSVCRT.puts
004026AC |.^ EB B2 |jmp short 00402660
004026AE | 66:90 |nop
004026B0 |> 83F8 0C |cmp eax, 0C
004026B3 |. 75 1A |jne short 004026CF
004026B5 |. C70424 614040 |mov dword ptr [local.9], offset 0040406 ; /string => "That was case 12"
004026BC |. E8 B3FEFFFF |call <jmp.&msvcrt.puts> ; \MSVCRT.puts
004026C1 |.^ EB D1 |jmp short 00402694
004026C3 |> C70424 944040 |mov dword ptr [local.9], offset 0040409 ; /string => "That was case 14"
004026CA |. E8 A5FEFFFF |call <jmp.&msvcrt.puts> ; \MSVCRT.puts
004026CF |> C70424 A54040 |mov dword ptr [local.9], offset 004040A ; /string => "That was default"
004026D6 |. E8 99FEFFFF |call <jmp.&msvcrt.puts> ; \MSVCRT.puts
004026DB |.^ EB 83 \jmp short 00402660
004026DD | 8D76 00 lea esi, [esi]
004026E0 |> 31C0 xor eax, eax
Now the same in Masm32 SDK code:
include \masm32\include\masm32rt.inc
.code
start:
printf("Please enter an integer (123 to exit): ")
.While 1
switch val(input())
case 123
.break
case 12, 24, 16
printf("That was case 12, 24 or 16\n")
case 14
printf("That was case 14\n")
default
printf("That was default\n")
endsw
.Endw
exit
end start
Under the hood:
0040100E > /CC int3
0040100F . |68 04010000 push 104 ; /Arg2 = 104
00401014 . |68 60214000 push offset 00402160 ; |Arg1 = Switch.402160
00401019 . |E8 66000000 call 00401084 ; \Switch.00401084
0040101E . |68 60214000 push offset 00402160 ; /s
00401023 . |FF15 E4204000 call near [<&msvcrt.atoi>] ; \MSVCRT.atoi
00401029 . |83C4 04 add esp, 4
0040102C . |8BC0 mov eax, eax
0040102E . |83F8 7B cmp eax, 7B
00401031 . |75 04 jne short 00401037
00401033 . |EB 46 jmp short 0040107B
00401035 . |EB 42 jmp short 00401079
00401037 > |83F8 10 cmp eax, 10
0040103A . |74 0A je short 00401046
0040103C . |83F8 18 cmp eax, 18
0040103F . |74 05 je short 00401046
00401041 . |83F8 0C cmp eax, 0C
00401044 . |75 10 jne short 00401056
00401046 > |68 28204000 push offset 00402028 ; /format = "That was case 12, 24 or 16"
0040104B . |FF15 E0204000 call near [<&msvcrt.printf>] ; \MSVCRT.printf
00401051 . |83C4 04 add esp, 4
00401054 . |EB 23 jmp short 00401079
00401056 > |83F8 0E cmp eax, 0E
00401059 . |75 10 jne short 0040106B
0040105B . |68 48204000 push offset 00402048 ; /format = "That was case 14"
00401060 . |FF15 E0204000 call near [<&msvcrt.printf>] ; \MSVCRT.printf
00401066 . |83C4 04 add esp, 4
00401069 . |EB 0E jmp short 00401079
0040106B > |68 5C204000 push offset 0040205C ; /format = "That was default"
00401070 . |FF15 E0204000 call near [<&msvcrt.printf>] ; \MSVCRT.printf
00401076 . |83C4 04 add esp, 4
00401079 >^\EB 93 jmp short 0040100E
MasmBasic:
include \masm32\MasmBasic\MasmBasic.inc
Init
PrintLine "Please enter an integer (123 to exit):"
.While 1
Switch_ Val(Input$("Please enter an integer: "))
Case_ 123
.break
Case_ 12, 24, 16
printf("That was case 12, 24 or 16\n")
Case_ 14
printf("That was case 14\n")
Default_
printf("That was default\n")
Endsw_
.Endw
EndOfCode
004010F9 . CC int3
004010FA . EB 30 jmp short 0040112C
004010FC > EB 53 jmp short 00401151 ; break
004010FE . C3 retn
004010FF > 68 7A704000 push offset 0040707A ; /format = "That was case 12, 24 or 16"
00401104 . FF15 84794000 call near [<&msvcrt.printf>] ; \MSVCRT.printf
0040110A . 83C4 04 add esp, 4
0040110D . C3 retn ; Jump to 40114C
0040110E > 68 98704000 push offset 00407098 ; /format = "That was case 14"
00401113 . FF15 84794000 call near [<&msvcrt.printf>] ; \MSVCRT.printf
00401119 . 83C4 04 add esp, 4
0040111C . C3 retn ; Jump to 40114C
0040111D > 68 AC704000 push offset 004070AC ; /format = "That was default"
00401122 . FF15 84794000 call near [<&msvcrt.printf>] ; \MSVCRT.printf
00401128 . 83C4 04 add esp, 4
0040112B . C3 retn ; Jump to 40114C
0040112C > 68 4C114000 push 0040114C
00401131 . 83F8 7B cmp eax, 7B
00401134 .^ 74 C6 je short 004010FC ; break
00401136 . 83F8 0C cmp eax, 0C
00401139 .^ 74 C4 je short 004010FF ; case 12
0040113B . 83F8 18 cmp eax, 18
0040113E .^ 74 BF je short 004010FF ; case 24
00401140 . 83F8 10 cmp eax, 10
00401143 .^ 74 BA je short 004010FF ; case 16
00401145 . 83F8 0E cmp eax, 0E
00401148 .^ 74 C4 je short 0040110E ; case 14
0040114A .^ EB D1 jmp short 0040111D ; case default
Clang 13.0 :tongue:
main: # @main
push rbp
mov rbp, rsp
sub rsp, 32
mov dword ptr [rbp - 4], 0
mov dword ptr [rbp - 8], edi
mov qword ptr [rbp - 16], rsi
movabs rdi, offset .L.str
mov al, 0
call printf
.LBB0_1: # =>This Inner Loop Header: Depth=1
movabs rdi, offset .L.str.1
lea rsi, [rbp - 24]
mov al, 0
call __isoc99_scanf
cmp eax, 123
je .LBB0_11
cmp dword ptr [rbp - 24], 12
jne .LBB0_4
int3
.LBB0_4: # in Loop: Header=BB0_1 Depth=1
mov eax, dword ptr [rbp - 24]
add eax, -12
mov ecx, eax
mov qword ptr [rbp - 32], rcx # 8-byte Spill
sub eax, 12
ja .LBB0_9
mov rax, qword ptr [rbp - 32] # 8-byte Reload
mov rax, qword ptr [8*rax + .LJTI0_0]
jmp rax
.LBB0_5: # in Loop: Header=BB0_1 Depth=1
movabs rdi, offset .L.str.2
mov al, 0
call printf
.LBB0_6: # in Loop: Header=BB0_1 Depth=1
movabs rdi, offset .L.str.3
mov al, 0
call printf
.LBB0_7: # in Loop: Header=BB0_1 Depth=1
movabs rdi, offset .L.str.4
mov al, 0
call printf
jmp .LBB0_10
.LBB0_8: # in Loop: Header=BB0_1 Depth=1
movabs rdi, offset .L.str.5
mov al, 0
call printf
.LBB0_9: # in Loop: Header=BB0_1 Depth=1
movabs rdi, offset .L.str.6
mov al, 0
call printf
.LBB0_10: # in Loop: Header=BB0_1 Depth=1
jmp .LBB0_1
.LBB0_11:
mov eax, dword ptr [rbp - 4]
add rsp, 32
pop rbp
ret
.LJTI0_0:
.quad .LBB0_5
.quad .LBB0_9
.quad .LBB0_8
.quad .LBB0_9
.quad .LBB0_7
.quad .LBB0_9
.quad .LBB0_9
.quad .LBB0_9
.quad .LBB0_9
.quad .LBB0_9
.quad .LBB0_9
.quad .LBB0_9
.quad .LBB0_6
.L.str:
.asciz "Please enter an integer: "
.L.str.1:
.asciz "%d"
.L.str.2:
.asciz "That was case 12\n"
.L.str.3:
.asciz "That was case 24\n"
.L.str.4:
.asciz "That was case 16\n"
.L.str.5:
.asciz "That was case 14\n"
.L.str.6:
.asciz "That was default\n"
Intel C++ Compiler 2021.5
.L_2__STRING.0:
.long 1634036816
.long 1696621939
.long 1919251566
.long 544104736
.long 1702129257
.long 980575591
.word 32
.L_2__STRING.6:
.word 25637
.byte 0
.L_2__STRING.1:
.long 1952540756
.long 1935767328
.long 1935762208
.long 842080357
.word 10
.L_2__STRING.2:
.long 1952540756
.long 1935767328
.long 1935762208
.long 875700325
.word 10
.L_2__STRING.3:
.long 1952540756
.long 1935767328
.long 1935762208
.long 909189221
.word 10
.L_2__STRING.4:
.long 1952540756
.long 1935767328
.long 1935762208
.long 875634789
.word 10
.L_2__STRING.5:
.long 1952540756
.long 1935767328
.long 1717920800
.long 1953264993
.word 10
main:
push rbp #2.34
mov rbp, rsp #2.34
sub rsp, 64 #2.34
mov DWORD PTR [-24+rbp], edi #2.34
mov QWORD PTR [-16+rbp], rsi #2.34
mov eax, offset flat: .L_2__STRING.0 #4.3
mov rdi, rax #4.3
mov eax, 0 #4.3
call printf #4.3
mov DWORD PTR [-64+rbp], eax #4.3
..B1.2: # Preds ..B1.22 ..B1.24 ..B1.18
mov eax, offset flat: .L_2__STRING.6 #5.10
lea rdx, QWORD PTR [-60+rbp] #5.10
mov rdi, rax #5.10
mov rsi, rdx #5.10
mov eax, 0 #5.10
call __isoc99_scanf #5.10
mov DWORD PTR [-56+rbp], eax #5.10
mov eax, DWORD PTR [-56+rbp] #5.10
cmp eax, 123 #5.29
je ..B1.15 # Prob 50% #5.29
mov eax, DWORD PTR [-60+rbp] #7.6
cmp eax, 12 #7.12
jne ..B1.6 # Prob 50% #7.12
int $3
..B1.6: # Preds ..B1.5 ..B1.4
mov eax, DWORD PTR [-60+rbp] #8.10
mov DWORD PTR [-52+rbp], eax #8.10
mov eax, DWORD PTR [-52+rbp] #8.10
cmp eax, 12 #8.10
je ..B1.10 # Prob 50% #8.10
mov eax, DWORD PTR [-52+rbp] #8.10
cmp eax, 24 #8.10
je ..B1.11 # Prob 50% #8.10
mov eax, DWORD PTR [-52+rbp] #8.10
cmp eax, 16 #8.10
je ..B1.12 # Prob 50% #8.10
mov eax, DWORD PTR [-52+rbp] #8.10
cmp eax, 14 #8.10
je ..B1.13 # Prob 50% #8.10
jmp ..B1.14 # Prob 100% #8.10
..B1.10: # Preds ..B1.6
mov eax, offset flat: .L_2__STRING.1 #11.2
mov rdi, rax #11.2
mov eax, 0 #11.2
call printf #11.2
mov DWORD PTR [-48+rbp], eax #11.2
..B1.11: # Preds ..B1.20 ..B1.7
mov eax, offset flat: .L_2__STRING.2 #13.2
mov rdi, rax #13.2
mov eax, 0 #13.2
call printf #13.2
mov DWORD PTR [-44+rbp], eax #13.2
..B1.12: # Preds ..B1.21 ..B1.8
mov eax, offset flat: .L_2__STRING.3 #15.2
mov rdi, rax #15.2
mov eax, 0 #15.2
call printf #15.2
mov DWORD PTR [-40+rbp], eax #15.2
jmp ..B1.2 # Prob 100% #15.2
..B1.13: # Preds ..B1.9
mov eax, offset flat: .L_2__STRING.4 #18.2
mov rdi, rax #18.2
mov eax, 0 #18.2
call printf #18.2
mov DWORD PTR [-36+rbp], eax #18.2
..B1.14: # Preds ..B1.23 ..B1.9
mov eax, offset flat: .L_2__STRING.5 #20.2
mov rdi, rax #20.2
mov eax, 0 #20.2
call printf #20.2
mov DWORD PTR [-32+rbp], eax #20.2
jmp ..B1.2 # Prob 100% #20.2
..B1.15: # Preds ..B1.3
mov eax, 0 #23.1
leave #23.1
ret #23.1
Kind of a tangent here, and not exactly on topic, but I'm curious: here's some of your "under the hood" code:
0040100E > /CC int3
0040100F . |68 04010000 push 104 ; /Arg2 = 104
00401014 . |68 60214000 push offset 00402160 ; |Arg1 = Switch.402160
00401019 . |E8 66000000 call 00401084 ; \Switch.00401084
0040101E . |68 60214000 push offset 00402160 ; /s
00401023 . |FF15 E4204000 call near [<&msvcrt.atoi>] ; \MSVCRT.atoi
00401029 . |83C4 04 add esp, 4
0040102C . |8BC0 mov eax, eax
0040102E . |83F8 7B cmp eax, 7B
00401031 . |75 04 jne short 00401037
00401033 . |EB 46 jmp short 0040107B
00401035 . |EB 42 jmp short 00401079
00401037 > |83F8 10 cmp eax, 10
0040103A . |74 0A je short 00401046
0040103C . |83F8 18 cmp eax, 18
0040103F . |74 05 je short 00401046
00401041 . |83F8 0C cmp eax, 0C
00401044 . |75 10 jne short 00401056
[...]
So the two lines I turned red: the first one does nothing. Doesn't set processor flags or anything else. Might as well have coded a NOP here.
Second one is an island that's never reached from any other part of the code.
Why would a compiler do such stupid things?
(I tried to format this as "code" but then you can't use the "color=" tag ... waaaah)
You are right, in fact I noticed that, too. It's a little flaw in the Masm32 and MasmBasic macros.