885509b1a2
Even though the table for how to expand packed unwind info at [1]
doesn't explicitly say this, this case is mentioned at [2] under the
case "Only x19 saved":
sub sp,sp,#16 // reg save area allocation*
stp x19,lr,[sp] // save x19, lr
sub sp,sp,#(framesz-16) // allocate the remaining local area
This was discussed and clarified at [3].
[1]
https://learn.microsoft.com/en-us/cpp/build/arm64-exception-handling?view=msvc-170#packed-unwind-data
[2]
https://learn.microsoft.com/en-us/cpp/build/arm64-exception-handling?view=msvc-170#arm64-stack-frame-layout
[3]
https://github.com/llvm/llvm-project/issues/169588#issuecomment-3581688753