Fix #81679: Tracing JIT crashes on reattaching #7776
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When a new process reattaches to OPcache, tracing JIT causes segfaults, because each new process allocates its own `zend_jit_traces` and `zend_jit_exit_groups` in SHM, although these need to be shared between all processes. We solve that by only allocating these structs for the first process, and store the pointers in `accel_shared_globals`, so we can reassign them when a new process reattaches.
dstogov
reviewed
Dec 15, 2021
dstogov
approved these changes
Dec 15, 2021
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Is this really good for PHP-8.0? |
Yeah. It's OK for PHP-8.0. opcache shared globals are not exported to other extensions. |
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When a new process reattaches to OPcache, tracing JIT causes segfaults,
because each new process allocates its own
zend_jit_tracesandzend_jit_exit_groupsin SHM, although these need to be shared betweenall processes.
We solve that by only allocating these structs for the first process,
and store the pointers in
accel_shared_globals, so we can reassignthem when a new process reattaches.
Well, this is more like a request for help than an actual pull request:
accel_shared_globalsseems viable, but there is likely a better solution. Anyway, thevoid *jit_tracesshould get the proper type.JIT_G(exit_counters)is still allocated in process memory?@dstogov, you may want to have a look at this. As is, tracing JIT apparently can't work in "reattaching environments" (i.e. most Windows stacks, except for Apache mpm_winnt). An alternative solution to let
zend_jit_startup()fail when reattaching, won't work, since the OPcode JIT handlers are still going to be executed.