runtime: callee saved r4 is destroyed unexpectedly in sigtramp@sys_darwin_arm.s #32744
Description
TEXT runtime·sigtramp(SB),NOSPLIT,$0
// Reserve space for callee-save registers and arguments.
SUB $36, R13
MOVW R4, 12(R13)
MOVW R5, 16(R13)
MOVW R6, 20(R13)
MOVW R7, 24(R13)
MOVW R8, 28(R13)
MOVW R11, 32(R13)
// Save arguments.
MOVW R0, 4(R13) // sig
MOVW R1, 8(R13) // info
MOVW R2, 12(R13) // ctx
The R4 is first stored to 12(R13), then R2 is also stored to 12(R13), so the original value in R4 is destroyed.