2  * Copyright 2013-2014 Andrew Turner.
3  * Copyright 2013-2014 Ian Lepore.
4  * Copyright 2013-2014 Rui Paulo.
19  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
47  * The ARM EABI specifies how to perform the frame unwinding in the
48  * Exception Handling ABI for the ARM Architecture document. To perform
49  * the unwind we need to know the initial frame pointer, stack pointer,
51  * index table that points to the function the program counter is within.
52  * This gives us either a list of three instructions to process, a 31-bit
53  * relative offset to a table of instructions, or a value telling us
56  * When we have the instructions to process we need to decode them
58  * patterns to encode that steps to take to update the stack pointer and
59  * link register to the correct values at the start of the function.
62 /* A special case when we are unable to unwind past this function */
101  * To unwind the stack through the code in a loaded module, we need to access
102  * the module's exidx unwind data.  To locate that data, one must search the
108  * function calls into this code to pass along the unwind info, which we save
111  * Because we have to help stack(9) gather stack info at any time, including in
113  * to walk the kernel's list of linker_file structs, because doing so requires
116  * synthesize at init time).  New entries are added to the end of this list as
118  * cleared out in-place to mark them as unused.  That means the code doing stack
120  * structure of the list never changes in a way that would cause the walker to
123  * A cleared-out entry on the list has module start=UINTPTR_MAX and end=0, so
125  * We also don't have to worry about races where we look up the unwind info just
126  * before a module is unloaded and try to access it concurrently with or just
128  * execution leads through a now-unloaded module, and that's already well into
129  * undefined-behavior territory.
141 			link;           /* Link to next entry */
146  * Hide ugly casting in somewhat-less-ugly macros.
147  *  CADDR - cast a pointer or number to caddr_t.
148  *  UADDR - cast a pointer or number to uintptr_t.
155  * module_start/end addresses are set to values that cannot match any real
162 	info->module_start = UINTPTR_MAX;  in clear_module_info()
163 	info->module_end   = 0;  in clear_module_info()
178 	info->exidx_start  = UADDR(lf->exidx_addr);  in populate_module_info()
179 	info->exidx_end    = UADDR(lf->exidx_addr) + lf->exidx_size;  in populate_module_info()
180 	info->module_start = UADDR(lf->address);  in populate_module_info()
181 	info->module_end   = UADDR(lf->address) + lf->size;  in populate_module_info()
185  * Create a new empty module_info entry and add it to the tail of the list.
201  * zero), then we're looking for an empty item to reuse, which is indicated by
202  * module_start being set to UINTPTR_MAX in the entry.
210 		if ((addr >= info->module_start && addr < info->module_end) ||  in find_module_info()
211 		    (addr == 0 && info->module_start == UINTPTR_MAX))  in find_module_info()
230 	if (lf->exidx_size == 0)  in unwind_module_loaded()
234 	 * Find an unused entry in the existing list to reuse.  If we don't find  in unwind_module_loaded()
236 	 * place the module_list is modified.  Adding a new entry to the list  in unwind_module_loaded()
239 	 * to prevent its module list from being modified, so we don't have to  in unwind_module_loaded()
258 	if (lf->exidx_size == 0)  in unwind_module_unloaded()
265 	if ((info = find_module_info(UADDR(lf->address))) == NULL) {  in unwind_module_unloaded()
267 		    lf->filename);  in unwind_module_unloaded()
274  * Initialization must run fairly early, as soon as malloc(9) is available, and
278  * the unwind tables might be stripped, so instead we have to use the
290 	thekernel.size       = UADDR(&_end) - UADDR(&_start);  in module_info_init()
292 	thekernel.exidx_size = UADDR(&_exidx_end) - UADDR(&_exidx_start);  in module_info_init()
299 /* Expand a 31-bit signed value to a 32-bit signed value */
308  * Perform a binary search of the index table to find the function
315 	unsigned int min, mid, max;  in find_index()  local
326 	max = (info->exidx_end - info->exidx_start) / sizeof(struct unwind_idx);  in find_index()
327 	start = (struct unwind_idx *)CADDR(info->exidx_start);  in find_index()
330 		mid = min + (max - min + 1) / 2;  in find_index()
332 		item = &start[mid];  in find_index()
334 		prel31_addr = expand_prel31(item->offset);  in find_index()
335 		func_addr = (uint32_t)&item->offset + prel31_addr;  in find_index()
338 			min = mid;  in find_index()
340 			max = mid - 1;  in find_index()
354 	insn = (*state->insn) >> (state->byte * 8);  in unwind_exec_read_byte()
357 	if (state->byte == 0) {  in unwind_exec_read_byte()
358 		state->byte = 3;  in unwind_exec_read_byte()
359 		state->insn++;  in unwind_exec_read_byte()
360 		state->entries--;  in unwind_exec_read_byte()
362 		state->byte--;  in unwind_exec_read_byte()
373 	uint32_t *vsp = (uint32_t *)state->registers[SP];  in unwind_exec_insn()
377 	if (state->entries == 0)  in unwind_exec_insn()
384 		state->registers[SP] += ((insn & INSN_VSP_SIZE_MASK) << 2) + 4;  in unwind_exec_insn()
387 		state->registers[SP] -= ((insn & INSN_VSP_SIZE_MASK) << 2) + 4;  in unwind_exec_insn()
396 		/* We have a refuse to unwind instruction */  in unwind_exec_insn()
413 				state->registers[reg] = *vsp++;  in unwind_exec_insn()
414 				state->update_mask |= 1 << reg;  in unwind_exec_insn()
426 		state->registers[SP] =  in unwind_exec_insn()
427 		    state->registers[insn & INSN_STD_DATA_MASK];  in unwind_exec_insn()
432 		/* Read how many registers to load */  in unwind_exec_insn()
446 			state->registers[reg] = *vsp++;  in unwind_exec_insn()
447 			state->update_mask |= 1 << reg;  in unwind_exec_insn()
454 			state->registers[14] = *vsp++;  in unwind_exec_insn()
459 		state->entries = 0;  in unwind_exec_insn()
480 				state->registers[reg] = *vsp++;  in unwind_exec_insn()
481 				state->update_mask |= 1 << reg;  in unwind_exec_insn()
491 		state->registers[SP] += 0x204 + (uleb128 << 2);  in unwind_exec_insn()
494 		/* We hit a new instruction that needs to be implemented */  in unwind_exec_insn()
502 		state->registers[SP] = (uint32_t)vsp;  in unwind_exec_insn()
507 	    state->registers[FP], state->registers[SP], state->registers[LR],  in unwind_exec_insn()
508 	    state->registers[PC]);  in unwind_exec_insn()
520 	/* Set PC to a known value */  in unwind_tab()
521 	state->registers[PC] = 0;  in unwind_tab()
524 	entry = *state->insn & ENTRY_MASK;  in unwind_tab()
527 		state->byte = 2;  in unwind_tab()
528 		state->entries = 1;  in unwind_tab()
530 		state->byte = 1;  in unwind_tab()
531 		state->entries = ((*state->insn >> 16) & 0xFF) + 1;  in unwind_tab()
539 	while (state->entries > 0) {  in unwind_tab()
547 	if (state->registers[PC] == 0) {  in unwind_tab()
548 		state->registers[PC] = state->registers[LR];  in unwind_tab()
553 		if (state->start_pc != state->registers[PC])  in unwind_tab()
554 			state->update_mask |= 1 << PC;  in unwind_tab()
565  * made to remove it after this new code has proven itself for a while.
573 	state->update_mask = 0;  in unwind_stack_one()
576 	state->start_pc = state->registers[PC];  in unwind_stack_one()
578 	/* Find the item to run */  in unwind_stack_one()
579 	index = find_index(state->start_pc);  in unwind_stack_one()
580 	if (index == NULL || index->insn == EXIDX_CANTUNWIND)  in unwind_stack_one()
583 	if (index->insn & (1U << 31)) {  in unwind_stack_one()
585 		state->insn = &index->insn;  in unwind_stack_one()
587 		/* A prel31 offset to the unwind table */  in unwind_stack_one()
588 		state->insn = (uint32_t *)  in unwind_stack_one()
589 		    ((uintptr_t)&index->insn +  in unwind_stack_one()
590 		     expand_prel31(index->insn));  in unwind_stack_one()
593 	/* Run the unwind function, return its finished/not-finished status. */  in unwind_stack_one()