JMP over a RET with a custom epilogue is incorrect

[sergey-sj]

;Strangely, forward JMP is correct but backward is not.

.386 .MODEL FLAT .CODE

Proc1 PROC NEAR test eax,eax; 85 C0 JNZ @@over ; 75 06 -ok test eax,eax; 85 C0 JNZ @@ret ; 75 00 -ok @@ret: CLC ; F8 RET ; C3

@@over: test eax,eax ; 85 C0 JNZ @@ret; 75 FA -ok test eax,eax ; 85 C0 JNZ @@ret; 75 F6 -ok Proc1 ENDP

TestEpilogue MACRO procname, flag, parmbytes, localbytes, reglist, userparms CLC RET ENDM

OPTION EPILOGUE:TestEpilogue

Proc2 PROC NEAR test eax,eax ; 85 C0 JZ @@over; 74 06 - ok test eax,eax ; 85 C0 JNZ @@ret; 75 00 - ok

@@ret: RET; F8 C3; epilogue ok

@@over: test eax,eax ; 85 C0 JNZ @@ret ; 75 FE - wrong - makes infinite loop test eax,eax ; 85 C0 JNZ @@ret; 75 FE - wrong Proc2 ENDP END

[john-terraspace]

I’ve tested this in ML and it’s fine, as a quick test (and this seems to work for me with hjwasm) can you change the label name from @@ret: to something else? I used @@xet: and make sure the ret instruction is on it’s own line.

Let me know if that solves the issue for you.

From: sergey-sj [mailto:notifications@github.com] Sent: 24 January 2017 12:29 PM To: Terraspace/HJWasm HJWasm@noreply.github.com Cc: Subscribed subscribed@noreply.github.com Subject: [Terraspace/HJWasm] JMP over a RET with a custom epilogue is incorrect (#47)

;Strangely, forward JMP is correct but backward is not.

.386 .MODEL FLAT .CODE

Proc1 PROC NEAR test eax,eax; 85 C0 JNZ @@over https://github.com/over ; 75 06 -ok test eax,eax; 85 C0 JNZ @@ret https://github.com/ret ; 75 00 -ok @@ret https://github.com/ret : CLC ; F8 RET ; C3

@@over https://github.com/over : test eax,eax ; 85 C0 JNZ @@ret https://github.com/ret ; 75 FA -ok test eax,eax ; 85 C0 JNZ @@ret https://github.com/ret ; 75 F6 -ok Proc1 ENDP

TestEpilogue MACRO procname, flag, parmbytes, localbytes, reglist, userparms CLC RET ENDM

OPTION EPILOGUE:TestEpilogue

Proc2 PROC NEAR test eax,eax ; 85 C0 JZ @@over https://github.com/over ; 74 06 - ok test eax,eax ; 85 C0 JNZ @@ret https://github.com/ret ; 75 00 - ok

@@ret https://github.com/ret : RET; F8 C3; epilogue ok

@@over https://github.com/over : test eax,eax ; 85 C0 JNZ @@ret https://github.com/ret ; 75 FE - wrong - makes infinite loop test eax,eax ; 85 C0 JNZ @@ret https://github.com/ret ; 75 FE - wrong Proc2 ENDP END

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[john-terraspace]

It seems like the issue is the epilogue macro being run on a line that has a label.

Just moving the ret to it’s own line seems to solve the issue.

Please confirm.

From: sergey-sj [mailto:notifications@github.com] Sent: 24 January 2017 12:29 PM To: Terraspace/HJWasm HJWasm@noreply.github.com Cc: Subscribed subscribed@noreply.github.com Subject: [Terraspace/HJWasm] JMP over a RET with a custom epilogue is incorrect (#47)

;Strangely, forward JMP is correct but backward is not.

.386 .MODEL FLAT .CODE

Proc1 PROC NEAR test eax,eax; 85 C0 JNZ @@over https://github.com/over ; 75 06 -ok test eax,eax; 85 C0 JNZ @@ret https://github.com/ret ; 75 00 -ok @@ret https://github.com/ret : CLC ; F8 RET ; C3

@@over https://github.com/over : test eax,eax ; 85 C0 JNZ @@ret https://github.com/ret ; 75 FA -ok test eax,eax ; 85 C0 JNZ @@ret https://github.com/ret ; 75 F6 -ok Proc1 ENDP

TestEpilogue MACRO procname, flag, parmbytes, localbytes, reglist, userparms CLC RET ENDM

OPTION EPILOGUE:TestEpilogue

Proc2 PROC NEAR test eax,eax ; 85 C0 JZ @@over https://github.com/over ; 74 06 - ok test eax,eax ; 85 C0 JNZ @@ret https://github.com/ret ; 75 00 - ok

@@ret https://github.com/ret : RET; F8 C3; epilogue ok

@@over https://github.com/over : test eax,eax ; 85 C0 JNZ @@ret https://github.com/ret ; 75 FE - wrong - makes infinite loop test eax,eax ; 85 C0 JNZ @@ret https://github.com/ret ; 75 FE - wrong Proc2 ENDP END

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[john-terraspace]

Confirmed that this behaviour isn't present for normal macros, ONLY the epilogue when on a line with a label.

; Disassembly of file: epi.obj ; Thu Jan 26 20:03:24 2017 ; Mode: 32 bits ; Syntax: MASM/ML ; Instruction set: 80386

.386 .model flat

public Proc1 public Proc3 public Proc2

_text SEGMENT DWORD PUBLIC 'CODE' ; section number 1

Proc1 PROC NEAR test eax, eax ; 0000 _ 85. C0 jnz ?002 ; 0002 75, 06 test eax, eax ; 0004 _ 85. C0 jnz ?001 ; 0006 75, 00 ?001: clc ; 0008 F8 ret ; 0009 _ C3 Proc1 ENDP

?002 LABEL NEAR test eax, eax ; 000A 85. C0 jnz ?001 ; 000C 75, FA test eax, eax ; 000E _ 85. C0 jnz ?001 ; 0010 75, F6

Proc3 LABEL NEAR test eax, eax ; 0012 _ 85. C0 jz ?004 ; 0014 74, 06 test eax, eax ; 0016 _ 85. C0 jnz ?003 ; 0018 75, 00 ?003: clc ; 001A F8 ret ; 001B _ C3

?004 LABEL NEAR test eax, eax ; 001C 85. C0 jnz ?003 ; 001E 75, FA test eax, eax ; 0020 _ 85. C0 jnz ?003 ; 0022 75, F6 ret ; 0024 _ C3

Proc2 PROC NEAR test eax, eax ; 0025 _ 85. C0 jz ?006 ; 0027 74, 06 test eax, eax ; 0029 _ 85. C0 jnz ?005 ; 002B 75, 00 ?005: clc ; 002D F8 ret ; 002E _ C3 Proc2 ENDP

?006 LABEL NEAR test eax, eax ; 002F 85. C0 jnz ?005 ; 0031 75, FA test eax, eax ; 0033 _ 85. C0 ; Note: Function does not end with ret or jmp jnz ?005 ; 0035 75, F6

_text ENDS

_data SEGMENT DWORD PUBLIC 'DATA' ; section number 2

_data ENDS

END

[sergey-sj]

Ok thanks, so there is a workaround - to place labels on separate lines.

Still there's something wrong with labels declared with a colon - two labels on the same line also don't work .CODE l1: l2: ;Error A2209: Syntax error l1:: l2: ;Error A2209: Syntax error

;labels in data segment don't work .DATA l1: DB ?; Error A2183: Use of register assumed to ERROR

Labels declared with LABEL are all ok, but they aren't scoped.

[john-terraspace]

I don’t think two labels on a line has ever worked in jwasm, but worth adding to the list to check.

Will check labels in data, that should work.

From: sergey-sj [mailto:notifications@github.com] Sent: 30 January 2017 10:09 AM To: Terraspace/HJWasm HJWasm@noreply.github.com Cc: John Hankinson john@terraspace.co.uk; Comment comment@noreply.github.com Subject: Re: [Terraspace/HJWasm] JMP over a RET with a custom epilogue is incorrect (#47)

Ok thanks, so there is a workaround - to place labels on separate lines.

Still there's something wrong with labels declared with a colon - two labels on the same line also don't work .CODE l1: l2: ;Error A2209: Syntax error l1:: l2: ;Error A2209: Syntax error

;labels in data segment don't work .DATA l1: DB ?; Error A2183: Use of register assumed to ERROR

Labels declared with LABEL are all ok, but they aren't scoped.

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[john-terraspace]

So the fix is more of a workaround, when using a custom epilogue macro, ensure that the ret is on it's own line without a label preceeding it.