frame marker) and the syscall stub frame info in the trap frame.
Previously we stored the stub frame info in (rp,pfs) and the
caller frame info in (iip,cfm). This ends up being suboptimal
for the following reasons:
1. When we create a new context, such as for an execve(2), we had
to set the (rp,pfs) pair for the entry point when using the
syscall path out of the kernel but we need to set the (iip,cfm)
pair when we take the interrupt way out. This is mostly just
an inconsistency from the kernel's point of view, but an ugly
irregularity from gdb(1)'s point of view.
2. The getcontext(2) and setcontext(2) syscalls had to swap the
(rp,pfs) and (iip,cfm) pairs to make the context compatible
with one created purely in userland.
Swapping the (rp,pfs) and (iip,cfm) pairs is visible to signal
handlers that actually peek at the mcontext_t and to gdb(1).
Since this change is made for gdb(1) and we don't care about
signal handlers that peek at the mcontext_t because we're still
a tier 2 platform, this ABI breakage is academic at this moment
in time.
Note that there was no real reason to save the caller frame info
in (iip,cfm) and the stub frame info in (rp,pfs).
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