Xu Kuohai <xukuohai@xxxxxxxxxxxxxxx> writes: > From: Xu Kuohai <xukuohai@xxxxxxxxxx> > > The arm64 jit blindly saves/restores all callee-saved registers, making > the jited result looks a bit too compliated. For example, for an empty > prog, the jited result is: > > 0: bti jc > 4: mov x9, lr > 8: nop > c: paciasp > 10: stp fp, lr, [sp, #-16]! > 14: mov fp, sp > 18: stp x19, x20, [sp, #-16]! > 1c: stp x21, x22, [sp, #-16]! > 20: stp x26, x25, [sp, #-16]! > 24: mov x26, #0 > 28: stp x26, x25, [sp, #-16]! > 2c: mov x26, sp > 30: stp x27, x28, [sp, #-16]! > 34: mov x25, sp > 38: bti j // tailcall target > 3c: sub sp, sp, #0 > 40: mov x7, #0 > 44: add sp, sp, #0 > 48: ldp x27, x28, [sp], #16 > 4c: ldp x26, x25, [sp], #16 > 50: ldp x26, x25, [sp], #16 > 54: ldp x21, x22, [sp], #16 > 58: ldp x19, x20, [sp], #16 > 5c: ldp fp, lr, [sp], #16 > 60: mov x0, x7 > 64: autiasp > 68: ret > > Clearly, there is no need to save/restore unused callee-saved registers. > This patch does this change, making the jited image to only save/restore > the callee-saved registers it uses. > > Now the jited result of empty prog is: > > 0: bti jc > 4: mov x9, lr > 8: nop > c: paciasp > 10: stp fp, lr, [sp, #-16]! > 14: mov fp, sp > 18: stp xzr, x26, [sp, #-16]! > 1c: mov x26, sp > 20: bti j // tailcall target > 24: mov x7, #0 > 28: ldp xzr, x26, [sp], #16 > 2c: ldp fp, lr, [sp], #16 > 30: mov x0, x7 > 34: autiasp > 38: ret > > Xu Kuohai (2): > bpf, arm64: Get rid of fpb > bpf, arm64: Avoid blindly saving/restoring all callee-saved registers > Acked-by: Puranjay Mohan <puranjay@xxxxxxxxxx> Thanks, Puranjay Mohan
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