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Date: Mon, 1 Aug 2022 06:12:26 +0800 (CST)
From: "lostxwind  (lostxwind AT 163 DOT com) [via djgpp-workers AT delorie DOT com]" <djgpp-workers AT delorie DOT com>
To: djgpp-workers AT delorie DOT com
Subject: Re:BUGREPORT: ___dpmi_get_raw_mode_switch_addr() modifies SI
 register and doesn't save it
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Sorry something went wrong with my email configuration, here's the original text (which was not availed in the mail list in base64 encoding), hope it works this time.

Hi,

I was trying to issue a bug report on delorie official site (https://www.delorie.com/djgpp/bugs/create.cgi) but failed as the database is closed. So I tried to contact you through email.

BUGREPROT:

BACKGROUND:
___dpmi_get_raw_mode_switch_addr() is needed to switch modes for some reason, instead of the __dpmi_simulate_real_mode_* class.
SYMPTOM:
Random crashes involving switch between real(/v86) mode and protected mode. 
REASON:
I found variables or function parameters corrupted after calling ___dpmi_get_raw_mode_switch_addr().
After reading the source code, I believe that the implementation of ___dpmi_get_raw_mode_switch_addr() has missed a single line that saves the ESI register.
src\libc\dpmi\api\d0306.S, line 2-line 4.

code before fix:
#define USE_EBX
#define USE_EDI
#include "dpmidefs.h"

possible fix:
#define USE_EBX
#define USE_EDI
#define USE_ESI
#include "dpmidefs.h"

Current workaround without bugfix:
Write a alternative implementation;
Or wrap the function call with asm that pushl/popl %esi.

Thanks,
crazii