X8
alias W8architectural number 8Indirect result location register
X864-bit view
X only
shared with W8
W832-bit view
bits 31:0 of X8
write
Writing W8 does not simply deposit 32 bits. Bits 63:32 of X8 are reset to zero as a side effect, so a W write always clears the upper half. This is the reason W8 and X8 can never hold unrelated values at the same time.
Notes
On AArch64, X8 holds the address of the return value when a function returns a large aggregate. It is also the conventional register for a dynamically resolved function address in PLT stubs.