std.debug: implement sparc*-linux unwinding
#25569
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cc @koachan you might be interested in this |
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… PowerPC As for SPARC, FP-based unwinding is superior on these.
flushw and ta 3 flush all windows *except* the current one. So we need to do this in a new register window to get all of the ones we care about.
It's better to do this here than in StackIterator.init() so that std.debug.cpu_context.Native.current() isn't a footgun on SPARC.
It's not really a ucontext_t at all. Lovely stuff.
We're overwriting the memory that unwind_context sits in, so we need to do the getFp() call earlier.
… on signal I have no idea if this is a QEMU bug or real kernel behavior. Either way, the register save area specifically exists for asynchronous spilling of incoming and local registers, so there should be no harm in doing this.
The FP would point to the register save area for the previous frame, while the SP points to the register save area for the current frame. So use the latter.
The return address points to the call instruction on SPARC, so the actual return address is 8 bytes after. This means that we shouldn't do the return address adjustment that we normally do.
The way SPARC works due to its ABI built around register windows means that we can always do fast FP-based unwinding.
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koachan
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Implements most of #25537.