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From: "Ozkan Sezer (sezeroz AT gmail DOT com) [via djgpp AT delorie DOT com]" <djgpp AT delorie DOT com>
Date: Sat, 24 Feb 2024 03:08:59 +0300
Message-ID: <CAA2C=vAMR_eEmGd01jZDe3013inxvtEM-0qB-yoCzsTF0Cx2zw@mail.gmail.com>
Subject: Re: checking int2d amis appstring with djgpp
To: djgpp AT delorie DOT com
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Reply-To: djgpp AT delorie DOT com

On Sat, Feb 24, 2024 at 12:49 AM J.W. Jagersma (jwjagersma AT gmail DOT com)
[via djgpp AT delorie DOT com] <djgpp AT delorie DOT com> wrote:
[...]
> >     __asm__ __volatile__ ("movw %%dx,%0":"=m"(addr.segment));
> >     __asm__ __volatile__ ("movw %%di,%0":"=m"(addr.offset16));
>
> This doesn't look right - you can't assume gcc preserves registers
> between asm blocks.

OK, should have been like this then, yes?

__asm__ __volatile__ (
  "movb %2,   %%ah\n"
  "xorb %%al, %%al\n"
  "int  $0x2D\n"
  "cmpb $0xFF,%%al\n"     /* is this a free multiplex? */
  "jz  1f\n"
  "xorw %%dx, %%dx\n"     /* it is, return NULL pointer */
  "xorw %%di, %%di\n"
  "1:\n"
  "movw %%dx, %0\n"
  "movw %%di, %1\n"
  : "=m"(addr.segment),
    "=m"(addr.offset16)
  :  "m"(mx) );

> But this is a real-mode interrupt, no?  So you would have to do it via
> __dpmi_int() here anyway, no asm involved.

Is the following correct ??

 int sndlib_sbemu_detect(void)
{
  __dpmi_raddr addr;
  uint32_t r_addr;
  __dpmi_regs regs;
  char* appstring;
  int mx;

  /* check for INT2D vector == NULL */
  __dpmi_get_real_mode_interrupt_vector(0x2D, &addr);
  r_addr = ((uint32_t)addr.segment<<4) + (uint32_t)addr.offset16;
  if (!r_addr) return -1;

  /* scan all multiplexes of INT 2D */
  for (mx = 0; mx < 256; mx++)
  {
    memset(&regs, 0, sizeof(regs));
    regs.h.ah = mx;
    __dpmi_int(0x2D, &regs);
    if (regs.h.al != 0xFF)
      continue;

    /* check for SBEMU application string */
    r_addr = ((uint32_t)regs.x.dx<<4) + (uint32_t)regs.x.di;
    if (!r_addr) continue;
    appstring = (char *)real2ptr(r_addr);
    if (memcmp(appstring + 8,"SBEMU",5) == 0)
      return mx;
  }

  return -1;
}

--
O.S.