Fasm 1.73 Many cmp one jz.

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Overclick

Joined: 11 Jul 2020
Posts: 670
Location: Ukraine

Overclick 23 Jul 2020, 20:20

It doesn't seems to work as you reloading reg0

Your code in fasm will looks like this:

Code:

macro cmp a,[b] {
     sub rsp,8
     irp c, b  \{
        cmp       a,c
        pushfq
        pop      a
        or        [rsp],a
     \}
     popfq
}

Final version of my one. It accepts any size of operands as usual cmp does (figured by compiler ofcourse)

Code:

macro cmp a,[b] {
     c=0
     forward
     c=c+1
     common
     if c > 1
        push rax
        push qword 0
     forward
        if `a in <'rax','eax','ax','ah','al'> | \
           `b in <'rax','eax','ax','ah','al'>
            mov      rax,[rsp+8]
        end if
        cmp          a,b
        lahf
        or           [rsp],ah
     common
        pop rax
        shl          ax,8
        sahf
        pop rax
     else
        cmp          a,b
     end if
}

Last edited by Overclick on 23 Jul 2020, 22:36; edited 1 time in total

23 Jul 2020, 20:20

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20461
Location: In your JS exploiting you and your system

revolution 23 Jul 2020, 22:05

Overclick: If any flag is set upon entry then the compares have no effect, and those same flags are always set upon exit.

Also, consider making c local to avoid clashes.

Code:

local c
;...
     if c > 1
        push rax
        pushq 0 ;reset all flags
     forward

Last edited by revolution on 23 Jul 2020, 22:27; edited 1 time in total

23 Jul 2020, 22:05

bitRAKE

Joined: 21 Jul 2003
Posts: 4081
Location: vpcmpistri

bitRAKE 23 Jul 2020, 22:12

Overclick wrote:

It doesn't seems to work as you reloading reg0

Your code in fasm will looks like this:

Code:

macro cmp a,[b] {
     sub rsp,8
     irp c, b  \{
        cmp       a,c
        pushfq
        pop      a
        or        [rsp],a
     \}
     popfq
}

not really. the flags aren't POP'd until the end. "if % = %%"

_________________
¯\(°_o)/¯ “languages are not safe - uses can be” Bjarne Stroustrup

23 Jul 2020, 22:12

Overclick

Joined: 11 Jul 2020
Posts: 670
Location: Ukraine

Overclick 23 Jul 2020, 22:23

bitRAKE, operand for cmp replaced for next interaction

revolution, you right.

23 Jul 2020, 22:23

bitRAKE

Joined: 21 Jul 2003
Posts: 4081
Location: vpcmpistri

bitRAKE 23 Jul 2020, 22:27

do you mean for:

Code:

compare r15, 1,2,3
compare r15, 6,7,8

Then yes, R15 would be overwritten.

_________________
¯\(°_o)/¯ “languages are not safe - uses can be” Bjarne Stroustrup

23 Jul 2020, 22:27

Overclick

Joined: 11 Jul 2020
Posts: 670
Location: Ukraine

Overclick 23 Jul 2020, 22:40

Edited last version, there also I'm worried about full pack of flags replaced to 0. That why I changed popfq to:

Code:

        pop rax
        shl          ax,8
        sahf
        pop rax

23 Jul 2020, 22:40

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