Linux SIGBUS — Bus Error Signal (Memory Alignment & Mapping)

Overview

Linux SIGBUS (signal 7) occurs from memory alignment violations, accessing beyond mapped file boundaries, or hardware bus errors on specific architectures.

Key Details

• SIGBUS (signal 7) indicates a bus error — the CPU cannot physically address the memory
• Different from SIGSEGV: SIGBUS is an addressing error, SIGSEGV is a permissions/unmapped error
• Most common on x86: accessing an mmap'd file beyond its actual size
• On SPARC/ARM: unaligned memory access (e.g., reading int from odd address)
• Can also occur from stack overflow into guard pages on some architectures

Common Causes

• Accessing memory-mapped file (mmap) beyond the file's actual size
• File truncated while another process has it memory-mapped
• Unaligned memory access on strict-alignment architectures (ARM, SPARC)
• Hardware bus error (rare — indicates physical hardware problem)
• Stack guard page violation (alternative to SIGSEGV for stack overflow)

Steps

1. 1Check if the program uses mmap: strace -e mmap,munmap ./program
2. 2Verify mapped file size has not changed: ls -la and compare to mmap size
3. 3For alignment issues: compile with -fsanitize=undefined to detect alignment violations
4. 4Use GDB to find the exact instruction: gdb ./program core > bt
5. 5Check dmesg for hardware bus errors if the issue is not software

Tags

More in Signal

Frequently Asked Questions