When gdb is debugging the AArch64 architecture, it provides the following special commands:
set debug aarch64show debug aarch64
When gdb is debugging the AArch64 architecture, if the Scalable Vector
Extension (SVE) is present, then gdb will provide the vector registers
$z0 through $z31, vector predicate registers $p0 through
$p15, and the $ffr register. In addition, the pseudo register
$vg will be provided. This is the vector granule for the current thread
and represents the number of 64-bit chunks in an SVE z register.
If the vector length changes, then the $vg register will be updated,
but the lengths of the z and p registers will not change. This
is a known limitation of gdb and does not affect the execution of the
target process.