X29
alias W29architectural number 29Frame pointer (FP)
X2964-bit view
X only
shared with W29
W2932-bit view
bits 31:0 of X29
write
Writing W29 does not simply deposit 32 bits. Bits 63:32 of X29 are reset to zero as a side effect, so a W write always clears the upper half. This is the reason W29 and X29 can never hold unrelated values at the same time.
Notes
Compilers commonly build a frame chain through X29 so that a debugger can walk the stack even when frame pointer omission is otherwise in effect.