tree 80ef79013e25026cca28a6c3a79c38769e9977af
parent 218074baa1ca19e52b6cb5df422f25f8203a5683
author Devon H. O'Dell <dhobsd@google.com> 1547487040 -0800
committer Devon H. O'Dell <dhobsd@google.com> 1547495686 -0800

[runtime] Re-land vdso traceback support with arm64 fixes

This reverts commit d659dafb9e9155ce062a8597bc2194cdcce17f2b, which
reverted 570718fb20e426ee5091b3f512966a5913feac87.

The original change was crashing because it assumed that R21 was not
modified. Syscalls marked as blocking called into
runtime.enter/exitsyscall, which trash R21. This caused the finalizer
code to store 0 in m.vdsoSP to fail (writing to some random place).

This change brings back the original code from
570718fb20e426ee5091b3f512966a5913feac87, adding a fix to grab the M
again after returning from runtime.exitsyscall to store 0 in m.vdsoSP.

Test: Was able to verify Go code crashing often on qemu arm64 in
570718fb20e426ee5091b3f512966a5913feac87, and no longer crashing with
this approach.

Change-Id: Ia44b78d52ef2cfa6d860914cd9a49adcaf1e7b40