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joncampbell123 / dosbox-x

DOSBox-X fork of the DOSBox project
GNU General Public License v2.0
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Disabling the FPU doesn’t stop Quake from running #5012

Open skitt opened 1 month ago

skitt commented 1 month ago

Describe the bug

Quake requires a FPU and on a real FPU-less system it aborts with “Error: Quake requires a floating-point processor”. Disabling the FPU in DOSBox-X doesn’t prevent Quake from running, I thought it would/should.

Steps to reproduce the behaviour

  1. Start DOSBox-X with dosbox-x -set "cpu fpu=false" -set "cpu cputype=pentium"
  2. Confirm that the logs show the corresponding warning: “WARNING: Disabling FPU support for this CPU type is unusual, may confuse DOS programs”
  3. NSSI and similar tools determine that there is no FPU
  4. Start Quake, it runs fine

Expected behavior

Quake should abort as described above.

What operating system(s) this bug have occurred on?

Debian 12

What version(s) of DOSBox-X have this bug?

2024.03

Used configuration

No response

Output log

No response

Additional information

I haven’t tried with FPU emulation disabled at build-time, see https://github.com/joncampbell123/dosbox-x/issues/4262

Quake (or rather, DJGPP) expects interrupt 7 to occur if it tries to run a floating-point instruction without a FPU. It seems this doesn’t happen on DOSBox-X.

Have you checked that no similar bug report(s) exist?

Code of Conduct & Contributing Guidelines

joncampbell123 commented 2 weeks ago

I'm able to cause Quake to crash by setting fpu=false.

skitt commented 2 weeks ago

That’s intriguing, I wonder what the difference is...