undefined reference 问题查找
undefined reference 问题查找
问题
当编译器在链接报 undefined symbol 时，大部分情况下都会给出函数的调用链，但有些情况下不会给出相关信息，所以需要手动查找
假设有如下代码：
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#include <variant>
int main()
{
std::variant<int,double> v = 1.1;
auto i = std::get<int>(v);
}
编译:
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arm-none-eabi-g++ test.cpp -fno-exceptions
如果部分嵌入式 C++ 库没有实现 abort 函数的定义，则会报错:
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$ arm-none-eabi-g++ test.cpp -fno-exceptions
d:/tools/arm gnu toolchain arm-none-eabi/12.2 rel1/bin/../lib/gcc/arm-none-eabi/12.2.1/../../../../arm-none-eabi/bin/ld.exe: d:/tools/arm gnu toolchain arm-none-eabi/12.2 rel1/bin/../lib/gcc/arm-none-eabi/12.2.1\libc.a(libc_a-exit.o): in function `exit':
exit.c:(.text.exit+0x28): undefined reference to `_exit'
d:/tools/arm gnu toolchain arm-none-eabi/12.2 rel1/bin/../lib/gcc/arm-none-eabi/12.2.1/../../../../arm-none-eabi/bin/ld.exe: d:/tools/arm gnu toolchain arm-none-eabi/12.2 rel1/bin/../lib/gcc/arm-none-eabi/12.2.1\libc.a(libc_a-abort.o): in function `abort':
abort.c:(.text.abort+0x10): undefined reference to `_exit'
解决过程
生成 .o 文件:
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arm-none-eabi-g++ -g -c test.cpp
使用 nm 工具(列出符号表)查找目录下引用了该函数的 .o 文件(假设是个大型项目，有很多文件)：
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find . -name '*.o' -exec sh -c 'nm -C {} | grep " U.* abort" >/dev/null && echo {}' \;
查找到其中的 ./test.o 使用了 abort:
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$ find . -name '*.o' -exec sh -c 'nm -C {} | grep " U.* abort" >/dev/null && echo {}' \;
./test.o
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$ nm -C test.o
00000000 t $a
00000000 t $a
00000000 t $a
00000000 t $a
00000000 t $a
00000000 t $a
00000000 t $a
00000000 t $a
00000000 t $a
00000000 t $a
00000000 t $a
00000000 t $a
00000000 t $a
00000044 t $d
00000000 r $d
00000068 t $d
00000000 W std::variant<int, double>::valueless_by_exception() const
00000000 W std::variant<int, double>::index() const
00000000 W std::__detail::__variant::_Variant_storage<true, int, double>::_M_valid() const
00000000 W std::__detail::__variant::_Uninitialized<int, true>::_M_get() &
00000000 W decltype(auto) std::__detail::__variant::__get<0u, std::variant<int, double>&>(std::variant<int, double>&)
00000000 W decltype(auto) std::__detail::__variant::__get_n<0u, std::__detail::__variant::_Variadic_union<int, double>&>(std::__detail::__variant::_Variadic_union<int, double>&)
00000000 W std::__throw_bad_variant_access(bool)
00000000 W std::__throw_bad_variant_access(char const*)
00000000 W int& std::get<int, int, double>(std::variant<int, double>&)
00000000 W std::variant_alternative<0u, std::variant<int, double> >::type& std::get<0u, int, double>(std::variant<int, double>&)
00000000 W std::__detail::__variant::_Variadic_union<int, double>& std::forward<std::__detail::__variant::_Variadic_union<int, double>&>(std::remove_reference<std::__detail::__variant::_Variadic_union<int, double>&>::type&)
00000000 W std::variant<int, double>& std::forward<std::variant<int, double>&>(std::remove_reference<std::variant<int, o
uble>&>::type&)
U abort
00000000 T main
使用 objdump 反汇编并查找引用路径：
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arm-none-eabi-objdump -Cd test.o | c++filt | grep -A10 -B10 'abort'
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$ arm-none-eabi-objdump -Cd test.o | c++filt | grep -A10 -B10 'abort'
68: 9999999a .word 0x9999999a
6c: 3ff19999 .word 0x3ff19999
Disassembly of section .text._ZSt26__throw_bad_variant_accessPKc:
00000000 <std::__throw_bad_variant_access(char const*)>:
0: e92d4800 push {fp, lr}
4: e28db004 add fp, sp, #4
8: e24dd008 sub sp, sp, #8
c: e50b0008 str r0, [fp, #-8]
10: ebfffffe bl 0 <abort>
Disassembly of section .text._ZSt26__throw_bad_variant_accessb:
00000000 <std::__throw_bad_variant_access(bool)>:
0: e92d4800 push {fp, lr}
4: e28db004 add fp, sp, #4
8: e24dd008 sub sp, sp, #8
c: e1a03000 mov r3, r0
10: e54b3005 strb r3, [fp, #-5]
14: e55b3005 ldrb r3, [fp, #-5]
可以发现是 varient 库内部 abort。
附件
test.objdump:
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test.o: file format elf32-littlearm
Disassembly of section .text:
00000000 <main>:
0: e92d4800 push {fp, lr}
4: e28db004 add fp, sp, #4
8: e24dd018 sub sp, sp, #24
c: e24b301c sub r3, fp, #28
10: e3a02000 mov r2, #0
14: e5832000 str r2, [r3]
18: e5832004 str r2, [r3, #4]
1c: e5832008 str r2, [r3, #8]
20: e583200c str r2, [r3, #12]
24: e28f303c add r3, pc, #60 ; 0x3c
28: e893000c ldm r3, {r2, r3}
2c: e50b201c str r2, [fp, #-28] ; 0xffffffe4
30: e50b3018 str r3, [fp, #-24] ; 0xffffffe8
34: e3a03001 mov r3, #1
38: e54b3014 strb r3, [fp, #-20] ; 0xffffffec
3c: e24b301c sub r3, fp, #28
40: e1a00003 mov r0, r3
44: ebfffffe bl 0 <main>
48: e1a03000 mov r3, r0
4c: e5933000 ldr r3, [r3]
50: e50b3008 str r3, [fp, #-8]
54: e3a03000 mov r3, #0
58: e1a00003 mov r0, r3
5c: e24bd004 sub sp, fp, #4
60: e8bd4800 pop {fp, lr}
64: e12fff1e bx lr
68: 9999999a .word 0x9999999a
6c: 3ff19999 .word 0x3ff19999
Disassembly of section .text._ZSt26__throw_bad_variant_accessPKc:
00000000 <std::__throw_bad_variant_access(char const*)>:
0: e92d4800 push {fp, lr}
4: e28db004 add fp, sp, #4
8: e24dd008 sub sp, sp, #8
c: e50b0008 str r0, [fp, #-8]
10: ebfffffe bl 0 <abort>
Disassembly of section .text._ZSt26__throw_bad_variant_accessb:
00000000 <std::__throw_bad_variant_access(bool)>:
0: e92d4800 push {fp, lr}
4: e28db004 add fp, sp, #4
8: e24dd008 sub sp, sp, #8
c: e1a03000 mov r3, r0
10: e54b3005 strb r3, [fp, #-5]
14: e55b3005 ldrb r3, [fp, #-5]
18: e3530000 cmp r3, #0
1c: 0a000002 beq 2c <std::__throw_bad_variant_access(bool)+0x2c>
20: e59f001c ldr r0, [pc, #28] ; 44 <std::__throw_bad_variant_access(bool)+0x44>
24: ebfffffe bl 0 <std::__throw_bad_variant_access(bool)>
28: ea000001 b 34 <std::__throw_bad_variant_access(bool)+0x34>
2c: e59f0014 ldr r0, [pc, #20] ; 48 <std::__throw_bad_variant_access(bool)+0x48>
30: ebfffffe bl 0 <std::__throw_bad_variant_access(bool)>
34: e1a00000 nop ; (mov r0, r0)
38: e24bd004 sub sp, fp, #4
3c: e8bd4800 pop {fp, lr}
40: e12fff1e bx lr
44: 00000000 .word 0x00000000
48: 00000020 .word 0x00000020
Disassembly of section .text._ZSt3getIiJidEERT_RSt7variantIJDpT0_EE:
00000000 <int& std::get<int, int, double>(std::variant<int, double>&)>:
0: e92d4800 push {fp, lr}
4: e28db004 add fp, sp, #4
8: e24dd010 sub sp, sp, #16
c: e50b0010 str r0, [fp, #-16]
10: e3a03000 mov r3, #0
14: e50b3008 str r3, [fp, #-8]
18: e51b0010 ldr r0, [fp, #-16]
1c: ebfffffe bl 0 <int& std::get<int, int, double>(std::variant<int, double>&)>
20: e1a03000 mov r3, r0
24: e1a00003 mov r0, r3
28: e24bd004 sub sp, fp, #4
2c: e8bd4800 pop {fp, lr}
30: e12fff1e bx lr
Disassembly of section .text._ZNSt8__detail9__variant7__get_nILj0ERNS0_15_Variadic_unionIJidEEEEEDcOT0_:
00000000 <decltype(auto) std::__detail::__variant::__get_n<0u, std::__detail::__variant::_Variadic_union<int, double>&>(std::__detail::__variant::_Variadic_union<int, double>&)>:
0: e92d4800 push {fp, lr}
4: e28db004 add fp, sp, #4
8: e24dd008 sub sp, sp, #8
c: e50b0008 str r0, [fp, #-8]
10: e51b0008 ldr r0, [fp, #-8]
14: ebfffffe bl 0 <decltype(auto) std::__detail::__variant::__get_n<0u, std::__detail::__variant::_Variadic_union<int, double>&>(std::__detail::__variant::_Variadic_union<int, double>&)>
18: e1a03000 mov r3, r0
1c: e1a00003 mov r0, r3
20: ebfffffe bl 0 <decltype(auto) std::__detail::__variant::__get_n<0u, std::__detail::__variant::_Variadic_union<int, double>&>(std::__detail::__variant::_Variadic_union<int, double>&)>
24: e1a03000 mov r3, r0
28: e1a00003 mov r0, r3
2c: e24bd004 sub sp, fp, #4
30: e8bd4800 pop {fp, lr}
34: e12fff1e bx lr
Disassembly of section .text._ZNSt8__detail9__variant5__getILj0ERSt7variantIJidEEEEDcOT0_:
00000000 <decltype(auto) std::__detail::__variant::__get<0u, std::variant<int, double>&>(std::variant<int, double>&)>:
0: e92d4800 push {fp, lr}
4: e28db004 add fp, sp, #4
8: e24dd008 sub sp, sp, #8
c: e50b0008 str r0, [fp, #-8]
10: e51b0008 ldr r0, [fp, #-8]
14: ebfffffe bl 0 <decltype(auto) std::__detail::__variant::__get<0u, std::variant<int, double>&>(std::variant<int, double>&)>
18: e1a03000 mov r3, r0
1c: e1a00003 mov r0, r3
20: ebfffffe bl 0 <decltype(auto) std::__detail::__variant::__get<0u, std::variant<int, double>&>(std::variant<int, double>&)>
24: e1a03000 mov r3, r0
28: e1a00003 mov r0, r3
2c: e24bd004 sub sp, fp, #4
30: e8bd4800 pop {fp, lr}
34: e12fff1e bx lr
Disassembly of section .text._ZSt3getILj0EJidEERNSt19variant_alternativeIXT_ESt7variantIJDpT0_EEE4typeERS4_:
00000000 <std::variant_alternative<0u, std::variant<int, double> >::type& std::get<0u, int, double>(std::variant<int, double>&)>:
0: e92d4800 push {fp, lr}
4: e28db004 add fp, sp, #4
8: e24dd008 sub sp, sp, #8
c: e50b0008 str r0, [fp, #-8]
10: e51b0008 ldr r0, [fp, #-8]
14: ebfffffe bl 0 <std::variant_alternative<0u, std::variant<int, double> >::type& std::get<0u, int, double>(std::variant<int, double>&)>
18: e1a03000 mov r3, r0
1c: e3530000 cmp r3, #0
20: 13a03001 movne r3, #1
24: 03a03000 moveq r3, #0
28: e20330ff and r3, r3, #255 ; 0xff
2c: e3530000 cmp r3, #0
30: 0a000004 beq 48 <std::variant_alternative<0u, std::variant<int, double> >::type& std::get<0u, int, double>(std::variant<int, double>&)+0x48>
34: e51b0008 ldr r0, [fp, #-8]
38: ebfffffe bl 0 <std::variant_alternative<0u, std::variant<int, double> >::type& std::get<0u, int, double>(std::variant<int, double>&)>
3c: e1a03000 mov r3, r0
40: e1a00003 mov r0, r3
44: ebfffffe bl 0 <std::variant_alternative<0u, std::variant<int, double> >::type& std::get<0u, int, double>(std::variant<int, double>&)>
48: e51b0008 ldr r0, [fp, #-8]
4c: ebfffffe bl 0 <std::variant_alternative<0u, std::variant<int, double> >::type& std::get<0u, int, double>(std::variant<int, double>&)>
50: e1a03000 mov r3, r0
54: e1a00003 mov r0, r3
58: e24bd004 sub sp, fp, #4
5c: e8bd4800 pop {fp, lr}
60: e12fff1e bx lr
Disassembly of section .text._ZNKSt7variantIJidEE5indexEv:
00000000 <std::variant<int, double>::index() const>:
0: e52db004 push {fp} ; (str fp, [sp, #-4]!)
4: e28db000 add fp, sp, #0
8: e24dd00c sub sp, sp, #12
c: e50b0008 str r0, [fp, #-8]
10: e51b3008 ldr r3, [fp, #-8]
14: e5d33008 ldrb r3, [r3, #8]
18: e1a00003 mov r0, r3
1c: e28bd000 add sp, fp, #0
20: e49db004 pop {fp} ; (ldr fp, [sp], #4)
24: e12fff1e bx lr
Disassembly of section .text._ZNKSt7variantIJidEE22valueless_by_exceptionEv:
00000000 <std::variant<int, double>::valueless_by_exception() const>:
0: e92d4800 push {fp, lr}
4: e28db004 add fp, sp, #4
8: e24dd008 sub sp, sp, #8
c: e50b0008 str r0, [fp, #-8]
10: e51b3008 ldr r3, [fp, #-8]
14: e1a00003 mov r0, r3
18: ebfffffe bl 0 <std::variant<int, double>::valueless_by_exception() const>
1c: e1a03000 mov r3, r0
20: e2233001 eor r3, r3, #1
24: e20330ff and r3, r3, #255 ; 0xff
28: e1a00003 mov r0, r3
2c: e24bd004 sub sp, fp, #4
30: e8bd4800 pop {fp, lr}
34: e12fff1e bx lr
Disassembly of section .text._ZSt7forwardIRSt7variantIJidEEEOT_RNSt16remove_referenceIS3_E4typeE:
00000000 <std::variant<int, double>& std::forward<std::variant<int, double>&>(std::remove_reference<std::variant<int, double>&>::type&)>:
0: e52db004 push {fp} ; (str fp, [sp, #-4]!)
4: e28db000 add fp, sp, #0
8: e24dd00c sub sp, sp, #12
c: e50b0008 str r0, [fp, #-8]
10: e51b3008 ldr r3, [fp, #-8]
14: e1a00003 mov r0, r3
18: e28bd000 add sp, fp, #0
1c: e49db004 pop {fp} ; (ldr fp, [sp], #4)
20: e12fff1e bx lr
Disassembly of section .text._ZSt7forwardIRNSt8__detail9__variant15_Variadic_unionIJidEEEEOT_RNSt16remove_referenceIS5_E4typeE:
00000000 <std::__detail::__variant::_Variadic_union<int, double>& std::forward<std::__detail::__variant::_Variadic_union<int, double>&>(std::remove_reference<std::__detail::__variant::_Variadic_union<int, double>&>::type&)>:
0: e52db004 push {fp} ; (str fp, [sp, #-4]!)
4: e28db000 add fp, sp, #0
8: e24dd00c sub sp, sp, #12
c: e50b0008 str r0, [fp, #-8]
10: e51b3008 ldr r3, [fp, #-8]
14: e1a00003 mov r0, r3
18: e28bd000 add sp, fp, #0
1c: e49db004 pop {fp} ; (ldr fp, [sp], #4)
20: e12fff1e bx lr
Disassembly of section .text._ZNRSt8__detail9__variant14_UninitializedIiLb1EE6_M_getEv:
00000000 <std::__detail::__variant::_Uninitialized<int, true>::_M_get() &>:
0: e52db004 push {fp} ; (str fp, [sp, #-4]!)
4: e28db000 add fp, sp, #0
8: e24dd00c sub sp, sp, #12
c: e50b0008 str r0, [fp, #-8]
10: e51b3008 ldr r3, [fp, #-8]
14: e1a00003 mov r0, r3
18: e28bd000 add sp, fp, #0
1c: e49db004 pop {fp} ; (ldr fp, [sp], #4)
20: e12fff1e bx lr
Disassembly of section .text._ZNKSt8__detail9__variant16_Variant_storageILb1EJidEE8_M_validEv:
00000000 <std::__detail::__variant::_Variant_storage<true, int, double>::_M_valid() const>:
0: e52db004 push {fp} ; (str fp, [sp, #-4]!)
4: e28db000 add fp, sp, #0
8: e24dd00c sub sp, sp, #12
c: e50b0008 str r0, [fp, #-8]
10: e3a03001 mov r3, #1
14: e1a00003 mov r0, r3
18: e28bd000 add sp, fp, #0
1c: e49db004 pop {fp} ; (ldr fp, [sp], #4)
20: e12fff1e bx lr
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