Nios® II Processor Reference Guide

ID 683836
Date 8/28/2023
Document Table of Contents

7.9.3. Linux Operating System Call Interface

Table 85.  Signals for Unhandled Instruction-Related Exceptions
Exception Signal
Supervisor-only instruction address SIGSEGV
TLB permission violation (execute) SIGSEGV
Supervisor-only instruction SIGILL
Unimplemented instruction SIGILL
Illegal instruction SIGILL
Break instruction SIGTRAP
Supervisor-only data address SIGSEGV
Misaligned data address SIGBUS
Misaligned destination address SIGBUS
Division error SIGFPE
TLB Permission Violation (read) SIGSEGV
TLB Permission Violation (write) SIGSEGV

There are no floating-point exceptions. The optional floating point unit (FPU) does not support exceptions and any process wanting exact IEEE conformance needs to use a soft-float library (possibly accelerated by use of the attached FPU).

The break instruction in a user process might generate a SIGTRAP signal for that process, but is not required to. Userspace programs should not use the break instruction and userspace debuggers should not insert one. If no hardware debugger is connected, the OS should assure that the break instruction does not cause the system to stop responding.

For information about userspace debugging, refer to "Userspace Breakpoints”.

The page size is 4 KB. Virtual addresses in user mode are all below 2 GB due to the MMU design. The NULL page is not mapped.