linux-kernel - arch/loongarch/kernel/unwind_prologue.c:84 unwind_by_prologue() warn: unsigned 'frame

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Date:   Thu, 24 Nov 2022 00:36:54 +0800
From:   kernel test robot <lkp@...el.com>
To:     Qing Zhang <zhangqing@...ngson.cn>
Cc:     oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Huacai Chen <chenhuacai@...nel.org>
Subject: arch/loongarch/kernel/unwind_prologue.c:84 unwind_by_prologue()
 warn: unsigned 'frame_ra' is never less than zero.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head:   eb7081409f94a9a8608593d0fb63a1aa3d6f95d8
commit: 49aef111e2dae176a7708b532118f33f24289248 LoongArch: Add prologue unwinder support
date:   3 months ago
config: loongarch-randconfig-m031-20221120
compiler: loongarch64-linux-gcc (GCC) 12.1.0

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@...el.com>

smatch warnings:
arch/loongarch/kernel/unwind_prologue.c:84 unwind_by_prologue() warn: unsigned 'frame_ra' is never less than zero.

vim +/frame_ra +84 arch/loongarch/kernel/unwind_prologue.c

    41	
    42	static bool unwind_by_prologue(struct unwind_state *state)
    43	{
    44		struct stack_info *info = &state->stack_info;
    45		union loongarch_instruction *ip, *ip_end;
    46		unsigned long frame_size = 0, frame_ra = -1;
    47		unsigned long size, offset, pc = state->pc;
    48	
    49		if (state->sp >= info->end || state->sp < info->begin)
    50			return false;
    51	
    52		if (!kallsyms_lookup_size_offset(pc, &size, &offset))
    53			return false;
    54	
    55		ip = (union loongarch_instruction *)(pc - offset);
    56		ip_end = (union loongarch_instruction *)pc;
    57	
    58		while (ip < ip_end) {
    59			if (is_stack_alloc_ins(ip)) {
    60				frame_size = (1 << 12) - ip->reg2i12_format.immediate;
    61				ip++;
    62				break;
    63			}
    64			ip++;
    65		}
    66	
    67		if (!frame_size) {
    68			if (state->first)
    69				goto first;
    70	
    71			return false;
    72		}
    73	
    74		while (ip < ip_end) {
    75			if (is_ra_save_ins(ip)) {
    76				frame_ra = ip->reg2i12_format.immediate;
    77				break;
    78			}
    79			if (is_branch_ins(ip))
    80				break;
    81			ip++;
    82		}
    83	
  > 84		if (frame_ra < 0) {
    85			if (state->first) {
    86				state->sp = state->sp + frame_size;
    87				goto first;
    88			}
    89			return false;
    90		}
    91	
    92		if (state->first)
    93			state->first = false;
    94	
    95		state->pc = *(unsigned long *)(state->sp + frame_ra);
    96		state->sp = state->sp + frame_size;
    97		return !!__kernel_text_address(state->pc);
    98	
    99	first:
   100		state->first = false;
   101		if (state->pc == state->ra)
   102			return false;
   103	
   104		state->pc = state->ra;
   105	
   106		return !!__kernel_text_address(state->ra);
   107	}
   108	

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