Arm fault handler: add emulation of MRS instruction #2088
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When the user process executes MSR, MRS or System instructions, the processor raises an exception, with the exception code (EC) in the Exception Syndrome Register (ESR_EL1) set to 0x18 (trapped MSR, MRS or System instruction execution in AArch64 state), which should be treated as an illegal instruction and cause the kernel to send a SIGILL signal to the process. Amend the Arm implementation of is_illegal_instruction() so that it recognizes this type of exceptions.
This avoids multiple dereferences to the context pointer. No functional change.
Starting with Go version 1.23, the Golang runtime for Arm64 during initialization tries to retrieve the values of some system registers (via the MRS instruction) in order to evaluate the features implemented by the processor. This instruction causes a CPU exception, which the kernel handles by sending SIGILL to the user process; as a result, Go programs built with Go version 1.23 do to not work on Arm. Add emulation of the MRS instruction to retrieve the values of the system registers used by the Go runtime, so that Go 1.23 works properly on Arm.
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Starting with Go version 1.23, the Golang runtime for Arm64 during initialization tries to retrieve the values of some system registers (via the MRS instruction) in order to evaluate the features implemented by the processor. This instruction causes a CPU exception, which is not properly handled by the kernel; as a result, Go programs built with Go version 1.23 do to not work on Arm.
This change set adds emulation of the MRS instruction to retrieve the values of the system registers used by the Go runtime, so that Go 1.23 works properly on Arm.