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authorPaul Burton <paul.burton@mips.com>2018-11-07 23:14:00 +0000
committerPaul Burton <paul.burton@mips.com>2018-11-09 10:23:14 -0800
commit1975ed43ce67542befed188f6aed6a82cfaffd0b (patch)
tree05a793e45dad2239c041495da54d2db361c52fc3 /arch/mips/math-emu
parentcc97ab235f3fe32401ca198cebe6f42642e95770 (diff)
MIPS: Ensure emulated FP sets PF_USED_MATH
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
Diffstat (limited to 'arch/mips/math-emu')
-rw-r--r--arch/mips/math-emu/cp1emu.c7
1 files changed, 7 insertions, 0 deletions
diff --git a/arch/mips/math-emu/cp1emu.c b/arch/mips/math-emu/cp1emu.c
index 62deb025970b..82e2993c1a2c 100644
--- a/arch/mips/math-emu/cp1emu.c
+++ b/arch/mips/math-emu/cp1emu.c
@@ -2831,6 +2831,13 @@ int fpu_emulator_cop1Handler(struct pt_regs *xcp, struct mips_fpu_struct *ctx,
u16 *instr_ptr;
int sig = 0;
+ /*
+ * Initialize context if it hasn't been used already, otherwise ensure
+ * it has been saved to struct thread_struct.
+ */
+ if (!init_fp_ctx(current))
+ lose_fpu(1);
+
oldepc = xcp->cp0_epc;
do {
prevepc = xcp->cp0_epc;