Emulation of a math function fails for m68k Linux user mode

[Ahmed Karaman]

Please check the attached math-example.c file.
When running the m68k executable under QEMU, it results in an
"Illegal instruction" error.
Other targets don't produce this error.

Steps to reproduce the bug:

1. Download the math-example.c attached file.
2. Compile it by running:
   m68k-linux-gnu-gcc -O2 -static math-example.c -o math-example-m68k -lm
3. Run the executable with QEMU:
   /build/qemu-5.0.0/build-gcc/m68k-linux-user/qemu-m68k math-example-m68k

The output of execution is:
   Profiling function expm1f():
   qemu: uncaught target signal 4 (Illegal instruction) - core dumped
   Illegal instruction (core dumped)

Output when running on other targets:
   Profiling function expm1f():
     Elapsed time: 47 ms
     Control result: 71804.953125

[Laurent Vivier (laurent-vivier)]

Tracing gives me:

IN: expm1f
0x800005cc: fetoxm1x %fp2,%fp0
Disassembler disagrees with translator over instruction decoding
Please report this to <email address hidden>

(gdb) x/2hx 0x800005cc
0x800005cc: 0xf200 0x0808

The instruction is not implemented in qemu. I fix that.

[Laurent Vivier (laurent-vivier)]

Fix available.

Execution doesn't fail anymore:

  Profiling function expm1f():
    Elapsed time: 41 ms
    Control result: 71805.108342

Control result matches real hardware one:

  Profiling function expm1f():
    Elapsed time: 2152 ms
    Control result: 71805.108342

[Thomas Huth (th-huth)]

Fixed here:
https://git.qemu.org/?p=qemu.git;a=commitdiff;h=250b1da35d579f423