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Emulated floating point instructions don't ensure that the PF_USED_MATH
flag is set for the task. This results in a couple of inconsistencies:
- ptrace will return the default initial state of FP registers rather
than the values actually stored in struct thread_struct, hiding
state that has been updated by emulated floating point instructions.
- If a task migrates to a CPU with an FPU after having emulated
floating point instructions then its floating point register state
will be reset to the default ~0 bit pattern, losing state from the
emulated instructions.
Fix this by calling init_fp_ctx() from fpu_emulator_cop1Handler() to
consistently initialize FP state if it was previously uninitialized,
setting the PF_USED_MATH flag in the process.
All callers of fpu_emulator_cop1Handler() either call lose_fpu(1) before
it in order to save any live FPU registers to struct thread_struct, or
in the case of do_cpu() already know that the task does not own an FPU
so lose_fpu(1) would be a no-op. Since we know that saving FP context
will be unnecessary in the case where FP context was just initialized we
move this call into fpu_emulator_cop1Handler() too, providing
consistency & avoiding needless duplication.
Calls to own_fpu(1) are common after return from
fpu_emulator_cop1Handler() too, but this would not be a no-op in the
do_cpu() case so these are left as-is. A potential future improvement
could be to have fpu_emulator_cop1Handler() restore FPU state
automatically only if it saved it, though this may not be optimal if
some callers are better off without their current calls to own_fpu(1).
One potential example of this could be mipsr2_decoder() which as-is
could end up saving & restoring FP context repeatedly & unnecessarily if
emulating multiple FP instructions.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Patchwork: https://patchwork.linux-mips.org/patch/21003/
Cc: linux-mips@linux-mips.org
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| .. | ||
| cp1emu.c | ||
| dp_2008class.c | ||
| dp_add.c | ||
| dp_cmp.c | ||
| dp_div.c | ||
| dp_fint.c | ||
| dp_flong.c | ||
| dp_fmax.c | ||
| dp_fmin.c | ||
| dp_fsp.c | ||
| dp_maddf.c | ||
| dp_mul.c | ||
| dp_rint.c | ||
| dp_simple.c | ||
| dp_sqrt.c | ||
| dp_sub.c | ||
| dp_tint.c | ||
| dp_tlong.c | ||
| dsemul.c | ||
| ieee754.c | ||
| ieee754.h | ||
| ieee754d.c | ||
| ieee754dp.c | ||
| ieee754dp.h | ||
| ieee754int.h | ||
| ieee754sp.c | ||
| ieee754sp.h | ||
| Makefile | ||
| me-debugfs.c | ||
| sp_2008class.c | ||
| sp_add.c | ||
| sp_cmp.c | ||
| sp_div.c | ||
| sp_fdp.c | ||
| sp_fint.c | ||
| sp_flong.c | ||
| sp_fmax.c | ||
| sp_fmin.c | ||
| sp_maddf.c | ||
| sp_mul.c | ||
| sp_rint.c | ||
| sp_simple.c | ||
| sp_sqrt.c | ||
| sp_sub.c | ||
| sp_tint.c | ||
| sp_tlong.c | ||