Draft: allow using an external symbol as a semaphore#26
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bonzini wants to merge 6 commits intocuviper:masterfrom
Draft
Draft: allow using an external symbol as a semaphore#26bonzini wants to merge 6 commits intocuviper:masterfrom
bonzini wants to merge 6 commits intocuviper:masterfrom
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Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
As a step towards allowing user-provided semaphores, move from "static mut" to properly annotated interior mutability. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
In preparation for allowing semaphores declared outside the probe_lazy macro, split platform_probe_lazy in two: one macro to place the semaphore in the .probes section, one to create the tracepoint. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Change the macro argument from ident to path. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
For now, this is kept internal and not documented. However, it will be used by QEMU to let C code declare the semaphores. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Ensure that Semaphore is documented properly. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
bonzini
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Sep 25, 2025
| // put it in the stapsdt note. The program cannot really do | ||
| // anything with it---the only available method is enabled(); therefore, | ||
| // even though not placing it in the .probes section could upset the tracing | ||
| // tool, it cannot be used to trigger undefined behavior. |
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This is worth pointing out—here I assume that the tools are robust enough and will either complain or ignore the probe, but not mess themselves up.
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CI run at bonzini#3 |
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In QEMU, each probe point has the address of its semaphore stored in a table, so that it's possible to observe which semaphores are enabled and which are not.
While in principle it is possible for a single (provider, name) pair to be associated to multiple semaphores, support for this is sometimes buggy so it's preferable to have a single semaphore shared between C code (which is where the table lies) and Rust invocations of
probe_lazy!.This series modifies
probe_lazy!so that:Semaphoreprobe_lazy!, as long as it has static lifetime.Semaphorereplaces thestatic mutsemaphore with anUnsafeCellwrapper that only allows reading. Alternatively, it could also use anAtomicU16, and the volatile read would be replaced with a relaxed load.