WIP: save registers of tasks that were active right before GC on a ucontext_t for conservative scanning #55003
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One clarification: this call allows us to get the contexts of the tasks that were scheduled right before GC started (i.e. the tasks that read from the safe-point page and incurred a segmentation fault). Getting register/stack-pointer information for tasks that were de-scheduled when GC started is easier because they were saved in a |
…ontext_t for conservative scanning
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fingolfin
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Jul 3, 2024
| // Requires `GC_SAVE_CONTEXT_FOR_CONSERVATIVE_SCANNING` to be defined. | ||
| // If ctx is NULL, the registers of the thread at the moment of the call are saved, else | ||
| // the registers of the context ctx are saved into the `ctx_at_the_time_gc_started` field of Julia's TLS. | ||
| JL_DLLEXPORT void jl_save_context_for_conservative_scanning(jl_ptls_t ptls, void *ctx); |
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It's not clear to me who would be calling this and when. And depending on the answer to that possibly also whether it is idempotent (i.e. if I accidentally call it twice, is that safe).
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Garbage collectors that are fully or partially conservative usually need to look at what was stored in the registers of the tasks right before GC started, and may also benefit from having information about the stack pointer at the time GC started in order to determine the lower/upper bounds of the stack.
Let's expose a call to support register saving for conservative GCs.
The current implementation is WIP because:
jl_ucontext_titself, instead of adding a new field to the TLS as I'm doing now.x86_64Linux for now.CC: @qinsoon, @kpamnany.