758eb020f7
On ARM and ARM64, during a VDSO call, the g register may be temporarily clobbered by the VDSO code. If a signal is received during the execution of VDSO code, we may not find a valid g reading the g register. In CL 192937, we conservatively assume g is nil. But this approach has a problem: we cannot handle the signal in this case. Further, if the signal is not a profiling signal, we'll call badsignal, which calls needm, which wants to get an extra m, but we don't have one in a non-cgo binary, which cuases the program to hang. This is even more of a problem with async preemption, where we will receive more signals than before. I ran into this problem while working on async preemption support on ARM64. In this CL, before making a VDSO call, we save the g on the gsignal stack. When we receive a signal, we will be running on the gsignal stack, so we can fetch the g from there and move on. We probably want to do the same for PPC64. Currently we rely on that the VDSO code doesn't actually clobber the g register, but this is not guaranteed and we don't have control with. Idea from discussion with Dan Cross and Austin. Should fix #34391. Change-Id: Idbefc5e4c2f4373192c2be797be0140ae08b26e3 Reviewed-on: https://go-review.googlesource.com/c/go/+/202759 Run-TryBot: Cherry Zhang <cherryyz@google.com> Reviewed-by: Austin Clements <austin@google.com> |
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