runtime: asyncPreempt should not try to save floating-point context for softfloat MIPS targets

[draganmladjenovic]

The GOMIPS_softfloat and GOMIPS64_softfloat defines can be used to conditionally compile floating-point context save/restore. It would be nice if assembler would error out when trying to use FP registers when targeting softfloat. Currently we silently end up with floating-point instructions in softfloat binaries.

go/src/runtime/preempt_mips64x.s

Lines 40 to 45 in cd9fd64

	MOVV FCR31, R1
	MOVV R1, 224(R29)
	MOVD F0, 232(R29)
	MOVD F1, 240(R29)
	MOVD F2, 248(R29)
	MOVD F3, 256(R29)

go/src/runtime/preempt_mipsx.s

Lines 40 to 45 in cd9fd64

	MOVW FCR31, R1
	MOVW R1, 112(R29)
	MOVF F0, 116(R29)
	MOVF F1, 120(R29)
	MOVF F2, 124(R29)
	MOVF F3, 128(R29)

@randall77
@cherrymui
@vstefanovic

[cherrymui]

Thanks for catching this! I'll send a fix.

[gopherbot]

Change https://golang.org/cl/222057 mentions this issue: runtime: don't save/restore FP registers in softfloat mode on MIPS(64)

[cherrymui]

We probably want to backport this to Go 1.14, otherwise it will SIGILL on softfloat MIPS machines.

@gopherbot please backport this to Go 1.14. Thanks.

[gopherbot]

Backport issue(s) opened: #37667 (for 1.14).

Remember to create the cherry-pick CL(s) as soon as the patch is submitted to master, according to https://golang.org/wiki/MinorReleases.

[gopherbot]

Change https://golang.org/cl/222062 mentions this issue: [release-branch.go1.14] runtime: don't save/restore FP registers in softfloat mode on MIPS(64)