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64 bit assembler => UASM Assembler Development => Topic started by: 2B||!2B on August 16, 2021, 10:37:56 AM

Title: Procedures without LOCAL's don't restore ESP from EBP
Post by: 2B||!2B on August 16, 2021, 10:37:56 AM

If a procedure has no LOCAL, it will not restore the stack from EBP.

Example of procedure with LOCAL

Code: [Select]

TESTPROC proc
LOCAL Dummy:DWORD

XOR EAX,EAX
ret

TESTPROC endp


Code: [Select]

PUSH EBP
MOV EBP,ESP
ADD ESP,-4
XOR EAX,EAX
MOV ESP,EBP
POP EBP
RETN 4

Removing LOCAL Dummy:DWORD would also make the procedure uses no MOV ESP,EBP before RET.

Code: [Select]

PUSH EBP
MOV EBP,ESP
XOR EAX,EAX
POP EBP
RETN 4

Is this the expected behavior or this is a bug?

Title: Re: Procedures without LOCAL's don't restore ESP from EBP
Post by: jj2007 on August 17, 2021, 03:50:29 AM

Expected behaviour. Masm and Watcom assemblers may differ slightly, e.g. using a leave before returning.

Title: Re: Procedures without LOCAL's don't restore ESP from EBP
Post by: 2B||!2B on August 17, 2021, 06:36:47 AM

I didn't know this until recently. I have used few PUSH's without re-balancing the stack and it was working with UASM v2.48 if I remember correctly. Must've been added recently...

Title: Re: Procedures without LOCAL's don't restore ESP from EBP
Post by: jj2007 on August 19, 2021, 12:15:54 AM

Quote from: 2B||!2B on August 17, 2021, 06:36:47 AM

I didn't know this until recently. I have used few PUSH's without re-balancing the stack and it was working with UASM v2.48 if I remember correctly. Must've been added recently...

Check your non-volatile registers (esi edi ebx) saved via uses :cool: