Arm64汇编：帧指针管理异常——递归斐波那契GDB回溯失效

以练习为目的实现了递归斐波那契函数，程序功能完全正常，但存在一个问题：使用GDB单步调试该函数时，backtrace（简称bt）命令无法正常工作。

源码 #

fib.s #

# fib.s
.data

.text
globl fib
fib:
stp x29, x30, [sp, #-16]!
mov x29, sp
# Recursive compute fib(n). Even though this is a really dumb way to do Fibonacci,
# this exercise is practically mandatory
# x0: uint64_t -> Result in x0
mov x1, #1
cmp x0, x1
ble root
# Gotta do some recursive shenanigans
stp x19, x20, [sp, #-16]!
sub x0, x0, 1
mov x19, x0
bl fib
mov x20, x0
mov x0, x19
sub x0, x0, 1
bl fib
add x0, x0, x20
ldp x19, x20, [sp], #16
root:
ldp x29, x30, [sp], #16
ret

main.c #

# main.c
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>

extern uint64_t fib(uint64_t);

int main() {
        uint64_t i;
        printf("Enter a number please: ");
        if (scanf("%lu", &i) == EOF) {
                printf("HOLY MOLY That's not a number");
                exit(1);
        }
        printf("Fib(%lu) = %lu\n", i, fib(i));
        exit(0);
}

编译步骤 #

mkdir -p build
gcc -g -Wall -Wextra -c main.c -o build/ul5_1.o
as -g fib.s -o ul5_2.o
ld -lc --entry main build/ul5* -o build/l5.o

调试异常现象 #

使用gdbtui启动调试，程序请求输入时输入4，会发现bt命令在执行到第二个stp指令前能正常工作，之后则会出现如下错误：

Backtrace stopped: Previous frame identical to this frame (corrupt stack?)

我认为fib函数符合AAPCS64规范，且栈管理正确，请问我遗漏了什么或哪里出错了？

内容的提问来源于stack exchange，提问作者pipsqueaker117