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gcc - ARM + gcc：main() 返回后不调用全局析构函数，但构造函数是

问题描述

我正在尝试写一个简单的“你好，世界！” Cortex-M0 CPU 的固件。目标是正确初始化和关闭 C++ 运行时，以便在 main() 之前调用全局构造函数，在main()之后调用全局析构函数。到目前为止，我设法让其中的一半正常工作——全局 ctor 正确运行，但全局析构函数却没有。我在 Windows 上使用 gcc 和Newlib，它应该初始化运行时。

struct Test {
    Test() // This is invoked correctly.
    {}

    ~Test() // This is not invoked at all.
    {}
};

Test test;

int main()
{
    return 0;
}

extern void __libc_init_array();
extern void __libc_fini_array();

void reset_handler() // This is the entry point.
{
    __libc_init_array(); // Test::Test().

    asm volatile( "bl main" ); // Invoke 'main'.

    __libc_fini_array(); // Expect Test::~Test() but nothing happens.
}

我已经做了很多研究，似乎对于 ARM 编译器应该为全局构造函数生成一个名为 .init_array 的部分，为全局析构函数生成一个名为.fini_array的部分，它在其中放置指向要调用的函数的指针。然后，链接器会将所有单元的节合并在一起，__libc_init_array将“遍历”该节并调用相应的函数。

这是链接描述文件的相关部分：

/* Initialization functions which run before main(),
       such as global constructors. */
.init_array : ALIGN( 4 ) {
    /* preinit data */
    PROVIDE_HIDDEN ( __preinit_array_start = . );
    KEEP( *( .preinit_array ) )
    PROVIDE_HIDDEN( __preinit_array_end = . );

    . = ALIGN(4);
    /* init data */
    PROVIDE_HIDDEN ( __init_array_start = . );
    KEEP( *( SORT( .init_array.* ) ) )
    KEEP(*(.init_array))
    PROVIDE_HIDDEN ( __init_array_end = . );
} > flash

/* Finalization functions which run after main(),
   such as global destructors. */
.fini_array : ALIGN( 4 ) {
    /* finit data */
    PROVIDE_HIDDEN (__fini_array_start = .);
    KEEP ( *( .fini_array.* ) )
    KEEP ( *( .fini_array ) )
    PROVIDE_HIDDEN (__fini_array_end = .);
} > flash

然而，让我担心的是，当我转储目标文件main.o甚至不是可执行文件时，我只能看到.init_array部分，但看不到.fini_array：

Sections:
Idx Name          Size      VMA       LMA       File off  Algn
  0 .group        00000008  00000000  00000000  00000034  2**2
                  CONTENTS, READONLY, GROUP, LINK_ONCE_DISCARD
  1 .group        00000008  00000000  00000000  0000003c  2**2
                  CONTENTS, READONLY, GROUP, LINK_ONCE_DISCARD
  2 .text         0000022c  00000000  00000000  00000044  2**2
                  CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
  3 .data         00000000  00000000  00000000  00000270  2**0
                  CONTENTS, ALLOC, LOAD, DATA
  4 .bss          00000001  00000000  00000000  00000270  2**2
                  ALLOC
  5 .text._ZN4TestC2Ev 00000012  00000000  00000000  00000270  2**1  << Test::Test()
                  CONTENTS, ALLOC, LOAD, READONLY, CODE
  6 .text._ZN4TestD2Ev 00000012  00000000  00000000  00000282  2**1  << Test::~Test()
                  CONTENTS, ALLOC, LOAD, READONLY, CODE
  7 .init_array   00000004  00000000  00000000  00000294  2**2    << WHERE IS .fini_array???
                  CONTENTS, ALLOC, LOAD, RELOC, DATA
  8 .debug_info   000012d9  00000000  00000000  00000298  2**0
                  CONTENTS, RELOC, READONLY, DEBUGGING, OCTETS
  9 .debug_abbrev 000003a1  00000000  00000000  00001571  2**0
                  CONTENTS, READONLY, DEBUGGING, OCTETS
 10 .debug_aranges 00000030  00000000  00000000  00001912  2**0
                  CONTENTS, RELOC, READONLY, DEBUGGING, OCTETS
 11 .debug_ranges 00000020  00000000  00000000  00001942  2**0
                  CONTENTS, RELOC, READONLY, DEBUGGING, OCTETS
 12 .debug_line   000002d2  00000000  00000000  00001962  2**0
                  CONTENTS, RELOC, READONLY, DEBUGGING, OCTETS
 13 .debug_str    000009e4  00000000  00000000  00001c34  2**0
                  CONTENTS, READONLY, DEBUGGING, OCTETS
 14 .comment      0000004d  00000000  00000000  00002618  2**0
                  CONTENTS, READONLY
 15 .debug_frame  0000054c  00000000  00000000  00002668  2**2
                  CONTENTS, RELOC, READONLY, DEBUGGING, OCTETS
 16 .ARM.attributes 0000002c  00000000  00000000  00002bb4  2**0
                  CONTENTS, READONLY

这就是我调用编译器的方式：

arm-none-eabi-c++.exe -o main.elf --verbose  -mcpu=cortex-m0 -mthumb --specs=nano.specs --entry reset_handler -T./../src/firmware.ld -ggdb -O0 -Wall -Wextra -Wpedantic -Werror ../src/main.cpp

这是日志：

GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 7a1ab17ae8404f635d46188cccacd8be
COLLECT_GCC_OPTIONS='-o' 'main.elf' '-v' '-mcpu=cortex-m0' '-mthumb' '-specs=nano.specs' '-e' 'reset_handler' '-T' './../src/firmware.ld' '-ggdb' '-O0' '-Wall' '-Wextra' '-Wpedantic' '-Werror' '-mfloat-abi=soft' '-march=armv6s-m'
 c:/id/gcc/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/bin/as.exe -v -march=armv6s-m -mfloat-abi=soft -meabi=5 
GNU assembler version 2.34.0 (arm-none-eabi) using BFD version (GNU Arm Embedded Toolchain 9-2020-q2-update) 2.34.0.20200428
COMPILER_PATH=c:/id/gcc/bin/../lib/gcc/arm-none-eabi/9.3.1/;c:/id/gcc/bin/../lib/gcc/;c:/id/gcc/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/bin/
LIBRARY_PATH=c:/id/gcc/bin/../lib/gcc/arm-none-eabi/9.3.1/thumb/v6-m/nofp/;c:/id/gcc/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v6-m/nofp/;c:/id/gcc/bin/../arm-none-eabi/lib/thumb/v6-m/nofp/;c:/id/gcc/bin/../lib/gcc/arm-none-eabi/9.3.1/;c:/id/gcc/bin/../lib/gcc/;c:/id/gcc/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/;c:/id/gcc/bin/../arm-none-eabi/lib/
COLLECT_GCC_OPTIONS='-o' 'main.elf' '-v' '-mcpu=cortex-m0' '-mthumb' '-specs=nano.specs' '-e' 'reset_handler' '-T' './../src/firmware.ld' '-ggdb' '-O0' '-Wall' '-Wextra' '-Wpedantic' '-Werror' '-mfloat-abi=soft' '-march=armv6s-m'
 c:/id/gcc/bin/../lib/gcc/arm-none-eabi/9.3.1/collect2.exe -plugin c:/id/gcc/bin/../lib/gcc/arm-none-eabi/9.3.1/liblto_plugin-0.dll -plugin-opt=c:/id/gcc/bin/../lib/gcc/arm-none-eabi/9.3.1/lto-wrapper.exe -plugin-opt=-fresolution=C:\Users\MAXID~1\AppData\Local\Temp\ccpOTkFN.res -plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lg_nano -plugin-opt=-pass-through=-lc_nano -plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lc_nano --sysroot=c:\id\gcc\bin\../arm-none-eabi -X -o main.elf -e reset_handler c:/id/gcc/bin/../lib/gcc/arm-none-eabi/9.3.1/thumb/v6-m/nofp/crti.o c:/id/gcc/bin/../lib/gcc/arm-none-eabi/9.3.1/thumb/v6-m/nofp/crtbegin.o c:/id/gcc/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v6-m/nofp/crt0.o -Lc:/id/gcc/bin/../lib/gcc/arm-none-eabi/9.3.1/thumb/v6-m/nofp -Lc:/id/gcc/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v6-m/nofp -Lc:/id/gcc/bin/../arm-none-eabi/lib/thumb/v6-m/nofp -Lc:/id/gcc/bin/../lib/gcc/arm-none-eabi/9.3.1 -Lc:/id/gcc/bin/../lib/gcc -Lc:/id/gcc/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib -Lc:/id/gcc/bin/../arm-none-eabi/lib C:\Users\MAXID~1\AppData\Local\Temp\cc1lU5Gg.o -lstdc++_nano -lm --start-group -lgcc -lg_nano -lc_nano --end-group --start-group -lgcc -lc_nano --end-group c:/id/gcc/bin/../lib/gcc/arm-none-eabi/9.3.1/thumb/v6-m/nofp/crtend.o c:/id/gcc/bin/../lib/gcc/arm-none-eabi/9.3.1/thumb/v6-m/nofp/crtn.o -T ./../src/firmware.ld
COLLECT_GCC_OPTIONS='-o' 'main.elf' '-v' '-mcpu=cortex-m0' '-mthumb' '-specs=nano.specs' '-e' 'reset_handler' '-T' './../src/firmware.ld' '-ggdb' '-O0' '-Wall' '-Wextra' '-Wpedantic' '-Werror' '-mfloat-abi=soft' '-march=armv6s-m'

公平地说，我对可能出现的问题一无所知 - 我尝试了默认的链接器脚本，.fini_array没有出现。想到的唯一想法是我的编译器是用某种禁用.fini_array部分的标志构建的？？？

任何想法将不胜感激！

更新：经过进一步调查，似乎析构函数与__cxa_atexit有更多关系......将进一步调查。

UPDATE2：感谢这里的精彩讨论https://forum.osdev.org/viewtopic.php?f=13&t=36728我添加了-fno-use-cxa-atexit，出现了.fini_array部分！

标签： gccarmglobaldestructornewlib

解决方案

好的，所以对于那些感兴趣的人来说，gcc 有两种方法可以生成对全局析构函数的调用。一种方法是通过__cxa_atexit。编译器会将一段代码注入到全局构造函数中，该构造函数使用__cxa_atexit注册该对象的析构函数。这样，当调用exit时，运行时“知道”要调用哪些析构函数。处理共享库的加载/卸载需要这种复杂性。

但是，也可以传递-fno-cxa-atexit标志，编译器会将对全局析构函数的调用放入.fini_array中。然后Newlib使用这个部分来调用析构函数。更多可以在这里找到：https ://forum.osdev.org/viewtopic.php?f=13&t=36728

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