linux - 从 _start 以外的函数调用 dlsym 崩溃

Question

我有这个工作正常的汇编程序：

SECTION .text

EXTERN dlopen ; loads a dynamic library
EXTERN dlsym ; retrieves the address for a symbol in the dynamic library

global _start ; "global" means that the symbol can be accessed in other modules. In order to refer to a global symbol from another module, you must use the "extern" keyboard
_start:

    ; load the library
    mov rdi, str_libX11so
    mov rsi, 2; RTLD_NOW=2
    call dlopen wrt ..plt
        ; PLT stands for Procedure Linkage Table:
        ; used to call external library functions whose address is not know at link time,
        ; so it must be resolved by the dynamic linker at run time
        ; more info: https://reverseengineering.stackexchange.com/questions/1992/what-is-plt-got
    mov [ptr_libX11so], rax ; the previous function call returned the value in rax

    ; load the function
    mov rdi, [ptr_libX11so]
    mov rsi, fstr_XOpenDisplay
    call dlsym wrt ..plt
    mov [fptr_XOpenDisplay], rax

    mov rax, 60 ; syscal: exit
    mov rdi, 0 ; return code
    syscall

str_libX11so: db "libX11.so", 0

; X11 function names
fstr_XOpenDisplay: db "XOpenDisplay", 0


SECTION .data
ptr_libX11so: dq 0 ; ptr to the X11 library

; X11 function ptrs
fptr_XOpenDisplay: dq 0

然后我尝试将调用的代码移动dlsym到函数（loadX11Functions）中。

SECTION .text

EXTERN dlopen ; loads a dynamic library
EXTERN dlsym ; retrieves the address for a symbol in the dynamic library

loadX11Functions:
    mov rdi, [ptr_libX11so]
    mov rsi, fstr_XOpenDisplay
    call dlsym wrt ..plt
    mov [fptr_XOpenDisplay], rax
    ret

global _start ; "global" means that the symbol can be accessed in other modules. In order to refer to a global symbol from another module, you must use the "extern" keyboard
_start:

    ; load the library
    mov rdi, str_libX11so
    mov rsi, 2; RTLD_NOW=2
    call dlopen wrt ..plt
        ; PLT stands for Procedure Linkage Table:
        ; used to call external library functions whose address is not know at link time,
        ; so it must be resolved by the dynamic linker at run time
        ; more info: https://reverseengineering.stackexchange.com/questions/1992/what-is-plt-got
    mov [ptr_libX11so], rax ; the previous function call returned the value in rax

    call loadX11Functions

    mov rax, 60 ; syscal: exit
    mov rdi, 0 ; return code
    syscall

str_libX11so: db "libX11.so", 0

; X11 function names
fstr_XOpenDisplay: db "XOpenDisplay", 0


SECTION .data
ptr_libX11so: dq 0 ; ptr to the X11 library

; X11 function ptrs
fptr_XOpenDisplay: dq 0

我很困惑，这么小的变化会破坏我的程序。

这是我用于编译的命令：

nasm -f elf64 -g -F dwarf minimal.asm && gcc -nostartfiles -no-pie minimal.o -ldl -o minimal && ./minimal

标签： linuxassemblynasmdlsym