C 是否可能知道变量所在的内存段？
在C程序中有没有办法知道变量所在的部分？例如：C 是否可能知道变量所在的内存段？,c,C,在C程序中有没有办法知道变量所在的部分？例如： char* str = "Word1"; char str2[] = "Word2"; printf("String1: %s | Location: %p\n", str, str); // <-- would be on the stack printf("String2: %s | Location: %p\n", str2, s
char* str = "Word1";
char str2[] = "Word2";
printf("String1: %s | Location: %p\n", str, str); // <-- would be on the stack
printf("String2: %s | Location: %p\n", str2, str2); // <-- would be in .rodata
etc.
char*str=“Word1”；
字符str2[]=“Word2”；
printf（“String1:%s |位置：%p\n”，str，str）；// C程序不可能绝对确定地知道其变量所在的部分。这就像海森堡测不准原理一样——仅仅获取一个变量的地址就可以使它存在于内存中，否则它可以通过优化完全消除
因此，使用readelf
或gdb
或objdump
，他们正在解码实际的可执行文件
原则上，ELF头应该加载到内存中，您可以从中推断出部分，您可以在Linux上阅读/proc/xx/maps
，等等，但是。。。除非我真的试图编写一个调试器、一个垃圾收集器或诸如此类的东西，否则我不会麻烦。部分取决于实现，我将重点介绍gcc
。您可以归档它，但它需要一些努力
如果您使用自己的链接器脚本，请跳过此步骤。提取链接器脚本：
ld--verbose>myls.ld
。该文件将包含比仅线性脚本更多的信息，因此需要对其进行编辑
我的默认链接器脚本：
OUTPUT_FORMAT("elf64-x86-64", "elf64-x86-64",
"elf64-x86-64")
OUTPUT_ARCH(i386:x86-64)
ENTRY(_start)
SEARCH_DIR("=/usr/local/lib/x86_64-linux-gnu"); SEARCH_DIR("=/lib/x86_64-linux-gnu"); SEARCH_DIR("=/usr/lib/x86_64-linux-gnu"); SEARCH_DIR("=/usr/lib/x86_64-linux-gnu64"); SEARCH_DIR("=/usr/local/lib64"); SEARCH_DIR("=/lib64"); SEARCH_DIR("=/usr/lib64"); SEARCH_DIR("=/usr/local/lib"); SEARCH_DIR("=/lib"); SEARCH_DIR("=/usr/lib"); SEARCH_DIR("=/usr/x86_64-linux-gnu/lib64"); SEARCH_DIR("=/usr/x86_64-linux-gnu/lib");
SECTIONS
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*(.gnu.warning)
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PROVIDE(_RODATA_S = .);
.rodata : { *(.rodata .rodata.* .gnu.linkonce.r.*) }
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PROVIDE(_RODATA_E = .);
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/* These sections are generated by the Sun/Oracle C++ compiler. */
.exception_ranges : ONLY_IF_RO { *(.exception_ranges*) }
/* Adjust the address for the data segment. We want to adjust up to
the same address within the page on the next page up. */
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PROVIDE_HIDDEN (__preinit_array_end = .);
}
.init_array :
{
PROVIDE_HIDDEN (__init_array_start = .);
KEEP (*(SORT_BY_INIT_PRIORITY(.init_array.*) SORT_BY_INIT_PRIORITY(.ctors.*)))
KEEP (*(.init_array EXCLUDE_FILE (*crtbegin.o *crtbegin?.o *crtend.o *crtend?.o ) .ctors))
PROVIDE_HIDDEN (__init_array_end = .);
}
.fini_array :
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KEEP (*(SORT_BY_INIT_PRIORITY(.fini_array.*) SORT_BY_INIT_PRIORITY(.dtors.*)))
KEEP (*(.fini_array EXCLUDE_FILE (*crtbegin.o *crtbegin?.o *crtend.o *crtend?.o ) .dtors))
PROVIDE_HIDDEN (__fini_array_end = .);
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KEEP (*crtbegin.o(.ctors))
KEEP (*crtbegin?.o(.ctors))
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KEEP (*(SORT(.ctors.*)))
KEEP (*(.ctors))
}
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KEEP (*(SORT(.dtors.*)))
KEEP (*(.dtors))
}
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.got.plt : { *(.got.plt) *(.igot.plt) }
.data :
{
*(.data .data.* .gnu.linkonce.d.*)
SORT(CONSTRUCTORS)
}
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_edata = .; PROVIDE (edata = .);
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*(.dynbss)
*(.bss .bss.* .gnu.linkonce.b.*)
*(COMMON)
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_end. Align after .bss to ensure correct alignment even if the
.bss section disappears because there are no input sections.
FIXME: Why do we need it? When there is no .bss section, we do not
pad the .data section. */
. = ALIGN(. != 0 ? 64 / 8 : 1);
}
.lbss :
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*(.dynlbss)
*(.lbss .lbss.* .gnu.linkonce.lb.*)
*(LARGE_COMMON)
}
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{
*(.lrodata .lrodata.* .gnu.linkonce.lr.*)
}
.ldata ALIGN(CONSTANT (MAXPAGESIZE)) + (. & (CONSTANT (MAXPAGESIZE) - 1)) :
{
*(.ldata .ldata.* .gnu.linkonce.l.*)
. = ALIGN(. != 0 ? 64 / 8 : 1);
}
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_end = .; PROVIDE (end = .);
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/* Stabs debugging sections. */
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/* SGI/MIPS DWARF 2 extensions */
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/* DWARF Extension. */
.debug_macro 0 : { *(.debug_macro) }
.debug_addr 0 : { *(.debug_addr) }
.gnu.attributes 0 : { KEEP (*(.gnu.attributes)) }
/DISCARD/ : { *(.note.GNU-stack) *(.gnu_debuglink) *(.gnu.lto_*) }
}
编辑链接器脚本：
在要检查的部分的开头和结尾添加符号。默认链接器脚本很可能已经添加了这些符号
在我的示例中，我将添加符号。这里是我为.rodata
段添加的内容。您需要为要跟踪的所有部分添加符号
PROVIDE(_RODATA_S = .); // <-- added
.rodata : { *(.rodata .rodata.* .gnu.linkonce.r.*) }
.rodata1 : { *(.rodata1) }
PROVIDE(_RODATA_E = .); // <-- added
PS链接器脚本及其修改：
OUTPUT_FORMAT("elf64-x86-64", "elf64-x86-64",
"elf64-x86-64")
OUTPUT_ARCH(i386:x86-64)
ENTRY(_start)
SEARCH_DIR("=/usr/local/lib/x86_64-linux-gnu"); SEARCH_DIR("=/lib/x86_64-linux-gnu"); SEARCH_DIR("=/usr/lib/x86_64-linux-gnu"); SEARCH_DIR("=/usr/lib/x86_64-linux-gnu64"); SEARCH_DIR("=/usr/local/lib64"); SEARCH_DIR("=/lib64"); SEARCH_DIR("=/usr/lib64"); SEARCH_DIR("=/usr/local/lib"); SEARCH_DIR("=/lib"); SEARCH_DIR("=/usr/lib"); SEARCH_DIR("=/usr/x86_64-linux-gnu/lib64"); SEARCH_DIR("=/usr/x86_64-linux-gnu/lib");
SECTIONS
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doesn't matter if the user does not
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linker won't look for a file to match a
wildcard. The wildcard also means that it
doesn't matter which directory crtbegin.o
is in. */
KEEP (*crtbegin.o(.ctors))
KEEP (*crtbegin?.o(.ctors))
/* We don't want to include the .ctor section from
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_end. Align after .bss to ensure correct alignment even if the
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FIXME: Why do we need it? When there is no .bss section, we do not
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IIRC[我可能错了]，没有去除调试/符号信息的ELF二进制文件将其与程序代码等一起映射到内存中（即，整个ELF文件被映射）。而且，libelf
[和/或libdl
]可以达到这个目的。但是，在包装器脚本中捕获和解析readelf
的输出并将输出文本文件传递给程序可能更容易。我真的做过那种[疯狂的]事情。但是，这是工作，所以一定要确定你真的想去做。@samuelbrody1249这可以通过一些努力和知识来完成。它可以像我的回答中那样存档。当然，方法可能会因使用的工具链而异感谢您提供这个非常详细的答案！如果可以这样称呼的话，链接器脚本是用什么语言编写的？用它自己的语言编写的
x points to .rodata
y points to .data
y is located in .data
fp points to .text
fp is located in .data
fp1 points to .text
fp1 is located in unknown
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