Mail Archives: djgpp/2023/01/24/16:54:56
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| Tue, 24 Jan 2023 10:10:22 -0800 (PST)
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Message-ID: | <5de28b44-10f2-c824-def1-d451035ecaad@gmail.com>
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Date: | Tue, 24 Jan 2023 19:10:21 +0100
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Subject: | [PING][PATCH v2] stub: ignore host exit status
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From: | "J.W. Jagersma (jwjagersma AT gmail DOT com) [via djgpp AT delorie DOT com]" <djgpp AT delorie DOT com>
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To: | djgpp AT delorie DOT com
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Would appreciate any feedback on this. I know there's a small mistake in one
comment, but the code works.
On 2022-11-25 00:26, J.W. Jagersma wrote:
> On 2022-11-23 20:47, J.W. Jagersma wrote:
>> Hi all,
>>
>> If you've ever tried using hdpmi32 with a djgpp program, you may have
>> noticed some strange behavior. The program first fails to run with
>> "Load error: no DPMI", but on the second try, it suddenly works. Then
>> a third invocation fails again, the fourth runs fine, etc.
>>
>> When you rename 'hdpmi32.exe' to 'cwsdpmi.exe', your program seems to
>> run consistently. But this is only because there is a second (real)
>> cwsdpmi in your PATH somewhere. What really happens, is that your
>> program alternates between running under hdpmi and cwsdpmi.
>>
>> I finally figured out why this happens, and it's very simple: hdpmi uses
>> the exit status to indicate if it was loaded via xms, vcpi, or int15.
>> And the djgpp stub considers any non-zero exit status to be a failure,
>> so it keeps searching PATH until cwsdpmi is found, which always returns
>> zero.
>>
>> For a possible solution, I would suggest to ignore the return status
>> from the host, and just check int 2f/1687 after every exec. As an added
>> bonus, this saves 13 bytes of stub space.
>
> Amended patch follows - it no longer skips the last iteration (exec
> with no path).
>
> It's a bit larger, but still saves 6 bytes in total.
>
> --- a/src/stub/stub.asm
> +++ b/src/stub/stub.asm
> @@ -199,38 +199,49 @@ not_path:
> ;-----------------------------------------------------------------------------
> ; Get DPMI information before doing anything 386-specific
>
> - push es
> push di
> - xor cx, cx ; flag for load attempt set cx = 0
> - jz @f2 ; We always jump, shorter than jmp
> + ; Set up loadname in case of no DPMI.
> + ; First try current dir.
> + xor ah, ah ; Copy until this character (=0)
> + call store_env_string ; copy stub image to "loadname"
> + mov si, bx ; remove name so we can add DPMI name
> + mov di, [path_off] ; Pointer to path contents (next try)
> @b1:
> + xor cx, cx ; flag to signal end of loop
> +@b2:
> + call check_dpmi ; int 2f, ax=1687
> + jz @f3
> + call do_exec ; copy our name to string and try load
> + jcxz @f1 ; cx=0 while we have more paths to try
> + call check_dpmi ; last chance...
> + jz @f3
> mov al, 110
> mov dx, msg_no_dpmi
> jmpl error
> -@b2:
> - or cx, cx
> - jnz @b1 ; we already tried load once before
> - inc cx
> - call load_dpmi
> - jc @b1
> +@f1:
> + ; Set up loadname for next attempt.
> + mov ah, ';' ; Copy until this character
> + call store_env_string ; to "loadname"
> + or al, al ; Check terminating character
> + jne @f2 ; If ';', continue
> + dec di ; else point at null for next pass.
> @f2:
> - mov ax, 0x1687 ; get DPMI entry point
> - int 0x2f
> - or ax, ax
> - jnz @b2 ; if 0 then it's there
> - and bl, 1 ; 32 bit capable?
> - jz @b2
> + inc cx
> + cmp si, loadname ; anything there?
> + je @b2 ; final try (no path)
> + mov al, [si-1]
> + call test_delim ; is final character a path delimiter
> + je @b1
> + movb [si], '\\' ; no, add separator between path & name
> + inc si
> + jmp @b1
> @f3:
> - mov [modesw], di ; store the DPMI entry point
> - mov [modesw+2], es
> - mov [modesw_mem], si
> pop di
> - pop es
>
> ;-----------------------------------------------------------------------------
> ; Now, find the name of the program file we are supposed to load.
>
> -; xor ah, ah ; termination character (set above!)
> +; xor ah, ah ; termination char (set by check_dpmi)
> call store_env_string ; copy it to loadname, set bx
>
> mov [stubinfo_env_size], di
> @@ -700,36 +711,29 @@ pm_dos:
> ret
>
> ;-----------------------------------------------------------------------------
> -; load DPMI server if not present
> -; First check directory from which stub is loaded, then path, then default
> -; On entry di points to image name
> +; Check for presence of a DPMI host, and save the mode switch address.
> +; Zero flag is clear on success. Clobbers ax/bx/dx.
>
> -path_off:
> - .dw 0 ; If stays zero, no path
> -
> -load_dpmi:
> - xor ah, ah ; Copy until this character (=0)
> - call store_env_string ; copy stub image to "loadname"
> - mov si, bx ; remove name so we can add DPMI name
> - mov di, [path_off] ; Pointer to path contents (next try)
> - jmp @f2
> -loadloop:
> - mov ah, ';' ; Copy until this character
> - call store_env_string ; to "loadname"
> - or al,al ; Check terminating character
> - jne @f1 ; If ';', continue
> - dec di ; else point at null for next pass.
> -@f1:
> - cmp si, loadname ; anything there?
> - je do_exec ; final try (no path) let it return
> - mov al, [si-1]
> - call test_delim ; is final character a path delimiter
> - je @f2
> - movb [si], '\\' ; no, add separator between path & name
> - inc si
> -@f2:
> - call do_exec ; copy our name to string and try load
> - jc loadloop
> +check_dpmi:
> + push es
> + push cx
> + push di
> + push si
> + mov ax, 0x1687 ; get DPMI entry point
> + int 0x2f
> + mov dx, bx
> + or dl, 1 ; bx bit 0: 32-bit capable
> + xor bx, dx
> + or ax, bx ; DPMI present if ax = 0
> + jnz @f1
> + mov [modesw], di ; store the DPMI entry point
> + mov [modesw+2], es
> + mov [modesw_mem], si
> +@f1:
> + pop si
> + pop di
> + pop cx
> + pop es
> ret
>
> ;-----------------------------------------------------------------------------
> @@ -766,13 +770,6 @@ do_exec:
> int 0x21
> pop di
> pop es
> - jc @f1 ;carry set if exec failed
> -
> - mov ah, 0x4d ;get return code
> - int 0x21
> - sub ax, 0x300 ;ah=3 TSR, al=code (success)
> - neg ax ;CY, if not originally 0x300
> -@f1:
> jmp restore_umb ;called func. return for us.
>
> ;-----------------------------------------------------------------------------
> @@ -796,10 +793,9 @@ include_umb:
> @f1:
> ret
>
> -; Restore upper memory status. All registers and flags preserved.
> +; Restore upper memory status. All registers preserved.
>
> restore_umb:
> - pushf
> cmpb [dos_major], 5 ; Won't work before dos 5
> jb @f1
> push ax
> @@ -815,7 +811,6 @@ restore_umb:
> pop bx
> pop ax
> @f1:
> - popf
> ret
>
> ;-----------------------------------------------------------------------------
> @@ -840,6 +835,8 @@ msg_no_selectors:
> .db "no DPMI selectors$"
> msg_no_dpmi_memory:
> .db "no DPMI memory$"
> +path_off:
> + .dw 0 ; Points to PATH, stays zero if none.
>
> ;-----------------------------------------------------------------------------
> ; Unstored Data, available during and after mode switch
>
- Raw text -