arch/nios2/kernel/misaligned.c

File Facts

System

Linux kernel

Corpus path

arch/nios2/kernel/misaligned.c

Extension

.c

Size

5464 bytes

Lines

239

Domain

Architecture Layer

Bucket

arch/nios2

Inferred role

Architecture Layer: implementation source

Status

source implementation candidate

Why This File Exists

CPU and platform-specific kernel glue: boot entry, traps, syscall entry, interrupts, page tables, context switch, and low-level barriers.

• CPU and platform-specific kernel glue: boot entry, traps, syscall entry, interrupts, page tables, context switch, and low-level barriers.
• Touches user memory; correctness depends on fault-safe copying and privilege boundary handling.
• Defines or uses C structs; map object ownership, embedded links, reference counts, and lock ownership.

Dependency Surface

• linux/errno.h
• linux/string.h
• linux/proc_fs.h
• linux/init.h
• linux/sched.h
• linux/uaccess.h
• linux/seq_file.h
• asm/traps.h
• linux/unaligned.h

Detected Declarations

• function get_reg_val
• function put_reg_val
• function handle_unaligned_c
• function instruction
• function misaligned_calc_reg_offsets
• function misaligned_init
• module init misaligned_init

Annotated Snippet

switch (isn & 0x3f) {
		case INST_LDHU:
			fault |= __get_user(d0, (u8 *)(addr+0));
			fault |= __get_user(d1, (u8 *)(addr+1));
			val = (d1 << 8) | d0;
			put_reg_val(fp, b, val);
			break;
		case INST_STH:
			val = get_reg_val(fp, b);
			d1 = val >> 8;
			d0 = val >> 0;
			if (in_kernel) {
				*(u8 *)(addr+0) = d0;
				*(u8 *)(addr+1) = d1;
			} else {
				fault |= __put_user(d0, (u8 *)(addr+0));
				fault |= __put_user(d1, (u8 *)(addr+1));
			}
			break;
		case INST_LDH:
			fault |= __get_user(d0, (u8 *)(addr+0));
			fault |= __get_user(d1, (u8 *)(addr+1));
			val = (short)((d1 << 8) | d0);
			put_reg_val(fp, b, val);
			break;
		case INST_STW:
			val = get_reg_val(fp, b);
			d3 = val >> 24;
			d2 = val >> 16;
			d1 = val >> 8;
			d0 = val >> 0;
			if (in_kernel) {
				*(u8 *)(addr+0) = d0;
				*(u8 *)(addr+1) = d1;
				*(u8 *)(addr+2) = d2;
				*(u8 *)(addr+3) = d3;
			} else {
				fault |= __put_user(d0, (u8 *)(addr+0));
				fault |= __put_user(d1, (u8 *)(addr+1));
				fault |= __put_user(d2, (u8 *)(addr+2));
				fault |= __put_user(d3, (u8 *)(addr+3));
			}
			break;
		case INST_LDW:
			fault |= __get_user(d0, (u8 *)(addr+0));
			fault |= __get_user(d1, (u8 *)(addr+1));
			fault |= __get_user(d2, (u8 *)(addr+2));
			fault |= __get_user(d3, (u8 *)(addr+3));
			val = (d3 << 24) | (d2 << 16) | (d1 << 8) | d0;
			put_reg_val(fp, b, val);
			break;
		}
	}

	addr = RDCTL(CTL_BADADDR);
	cause >>= 2;

	if (fault) {
		if (in_kernel) {
			pr_err("fault during kernel misaligned fixup @ %#lx; addr 0x%08x; isn=0x%08x\n",
				fp->ea, (unsigned int)addr,
				(unsigned int)isn);
		} else {
			pr_err("fault during user misaligned fixup @ %#lx; isn=%08x addr=0x%08x sp=0x%08lx pid=%d\n",
				fp->ea,
				(unsigned int)isn, addr, fp->sp,
				current->pid);

			_exception(SIGSEGV, fp, SEGV_MAPERR, fp->ea);
			return;
		}
	}

	/*
	 * kernel mode -
	 *  note exception and skip bad instruction (return)
	 */
	if (in_kernel) {
		fp->ea += 4;

		if (ma_usermode & KM_WARN) {
			pr_err("kernel unaligned access @ %#lx; BADADDR 0x%08x; cause=%d, isn=0x%08x\n",
				fp->ea,
				(unsigned int)addr, cause,
				(unsigned int)isn);
			/* show_regs(fp); */
		}

		return;
	}

Annotation

• Immediate include surface: `linux/errno.h`, `linux/string.h`, `linux/proc_fs.h`, `linux/init.h`, `linux/sched.h`, `linux/uaccess.h`, `linux/seq_file.h`, `asm/traps.h`.
• Detected declarations: `function get_reg_val`, `function put_reg_val`, `function handle_unaligned_c`, `function instruction`, `function misaligned_calc_reg_offsets`, `function misaligned_init`, `module init misaligned_init`.
• Atlas domain: Architecture Layer / arch/nios2.
• Implementation status: source implementation candidate.
• This snippet crosses the user/kernel memory boundary; validate fault handling and access checks before translating the pattern.

Implementation Notes

• This generated page is the file-by-file coverage layer; curated subsystem chapters should link here when they synthesize a multi-file control flow.
• Core OS pages should be promoted from atlas-only to deep-reviewed when they explain data structures, invariants, locking, lifecycle, and C implementation snippets.
• Driver-family pages are intentionally pattern-oriented unless they are part of the selected PCIe/NVMe representative device path.