我正在使用gdb和qemu的gdb-stub调试引导加载程序（syslinux）。在某些时候，主文件加载共享对象ldlinux.elf。
我想在gdb中为该文件添加符号。命令add-symbol-file似乎是要走的路。但是，作为可重定位文件，我必须指定它已加载的内存地址。这就是问题所在。
虽然我知道加载LOAD段的基地址，add-symbol-file按部分工作，并且要我指定每个部分加载的地址。
我可以告诉gdb加载我在内存中指定文件基址的所有部分的所有符号吗？
gdb的行为是否有效？节标题不用于运行ELF，甚至是可选的。我无法看到指定部分的加载地址的用例。
以下是共享对象的程序头和节头。
Elf file type is DYN (Shared object file) Entry point 0x4c60 There are 3 program headers, starting at offset 52 Program Headers: Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align LOAD 0x000000 0x00000000 0x00000000 0x1db10 0x20bfc RWE 0x1000 DYNAMIC 0x01d618 0x0001d618 0x0001d618 0x00098 0x00098 RW 0x4 GNU_STACK 0x000000 0x00000000 0x00000000 0x00000 0x00000 RWE 0x10 Section to Segment mapping: Segment Sections... 00 .gnu.hash .dynsym .dynstr .rel.dyn .rel.plt .plt .text .rodata .ctors .dtors .data.rel.ro .dynamic .got .got.plt .data .bss 01 .dynamic 02
There are 29 section headers, starting at offset 0x78618: Section Headers: [Nr] Name Type Addr Off Size ES Flg Lk Inf Al [ 0] NULL 00000000 000000 000000 00 0 0 0 [ 1] .gnu.hash GNU_HASH 00000094 000094 0007e0 04 A 2 0 4 [ 2] .dynsym DYNSYM 00000874 000874 0015c0 10 A 3 1 4 [ 3] .dynstr STRTAB 00001e34 001e34 0010f4 00 A 0 0 1 [ 4] .rel.dyn REL 00002f28 002f28 000ce8 08 A 2 0 4 [ 5] .rel.plt REL 00003c10 003c10 000568 08 AI 2 6 4 [ 6] .plt PROGBITS 00004180 004180 000ae0 04 AX 0 0 16 [ 7] .text PROGBITS 00004c60 004c60 013816 00 AX 0 0 4 [ 8] .rodata PROGBITS 00018480 018480 00462f 00 A 0 0 32 [ 9] .ctors INIT_ARRAY 0001cab0 01cab0 000010 00 WA 0 0 4 [10] .dtors FINI_ARRAY 0001cac0 01cac0 000004 00 WA 0 0 4 [11] .data.rel.ro PROGBITS 0001cae0 01cae0 000b38 00 WA 0 0 32 [12] .dynamic DYNAMIC 0001d618 01d618 000098 08 WA 3 0 4 [13] .got PROGBITS 0001d6b0 01d6b0 0000d0 04 WA 0 0 4 [14] .got.plt PROGBITS 0001d780 01d780 0002c0 04 WA 0 0 4 [15] .data PROGBITS 0001da40 01da40 0000d0 00 WA 0 0 32 [16] .bss NOBITS 0001db20 01db10 0030dc 00 WA 0 0 32 [17] .comment PROGBITS 00000000 01db10 000026 01 MS 0 0 1 [18] .debug_aranges PROGBITS 00000000 01db38 0010c0 00 0 0 8 [19] .debug_info PROGBITS 00000000 01ebf8 021ada 00 0 0 1 [20] .debug_abbrev PROGBITS 00000000 0406d2 009647 00 0 0 1 [21] .debug_line PROGBITS 00000000 049d19 00bd3a 00 0 0 1 [22] .debug_frame PROGBITS 00000000 055a54 004574 00 0 0 4 [23] .debug_str PROGBITS 00000000 059fc8 00538c 01 MS 0 0 1 [24] .debug_loc PROGBITS 00000000 05f354 01312d 00 0 0 1 [25] .debug_ranges PROGBITS 00000000 072481 0005d0 00 0 0 1 [26] .shstrtab STRTAB 00000000 072a51 000101 00 0 0 1 [27] .symtab SYMTAB 00000000 072b54 003530 10 28 504 4 [28] .strtab STRTAB 00000000 076084 002593 00 0 0 1 Key to Flags: W (write), A (alloc), X (execute), M (merge), S (strings) I (info), L (link order), G (group), T (TLS), E (exclude), x (unknown) O (extra OS processing required) o (OS specific), p (processor specific)
如果我尝试在地址0x7fab000加载文件，那么它将重新定位符号，以便.text部分从0x7fab000开始。
(gdb) add-symbol-file bios/com32/elflink/ldlinux/ldlinux.elf 0x7fab000
add symbol table from file "bios/com32/elflink/ldlinux/ldlinux.elf" at
.text_addr = 0x7fab000
(y or n) y
Reading symbols from bios/com32/elflink/ldlinux/ldlinux.elf...done.
然后所有符号都被0x4c60字节关闭。
答案 0 :(得分：7)
所以，最后，我用python和readelf工具制作了自己的命令。它不是很干净，因为它在子进程中运行readelf并解析其输出而不是直接解析ELF文件，但它可以工作（仅适用于32位ELF）。
它使用节头来生成并运行add-symbol-file命令，并正确地重新定位所有节。用法很简单，你给它elf文件和文件的基地址。由于remove-symbol-file只是给它提供了文件名，因此remove-symbol-file-all无法正常工作，我创建了remove-symbol-file -a address来生成并运行正确的(gdb) add-symbol-file-all bios/com32/elflink/ldlinux/ldlinux.elf 0x7fab000
add symbol table from file "bios/com32/elflink/ldlinux/ldlinux.elf" at
.text_addr = 0x7fafc50
.gnu.hash_addr = 0x7fab094
.dynsym_addr = 0x7fab874
.dynstr_addr = 0x7face34
.rel.dyn_addr = 0x7fadf28
.rel.plt_addr = 0x7faec08
.plt_addr = 0x7faf170
.rodata_addr = 0x7fc34e0
.ctors_addr = 0x7fc7af0
.dtors_addr = 0x7fc7b00
.data.rel.ro_addr = 0x7fc7b20
.dynamic_addr = 0x7fc8658
.got_addr = 0x7fc86f0
.got.plt_addr = 0x7fc87bc
.data_addr = 0x7fc8a80
.bss_addr = 0x7fc8b60
(gdb) remove-symbol-file-all bios/com32/elflink/ldlinux/ldlinux.elf 0x7fab000
命令。
.gdbinit以下是要添加到python
import subprocess
import re
def relocatesections(filename, addr):
p = subprocess.Popen(["readelf", "-S", filename], stdout = subprocess.PIPE)
sections = []
textaddr = '0'
for line in p.stdout.readlines():
line = line.decode("utf-8").strip()
if not line.startswith('[') or line.startswith('[Nr]'):
continue
line = re.sub(r' +', ' ', line)
line = re.sub(r'\[ *(\d+)\]', '\g<1>', line)
fieldsvalue = line.split(' ')
fieldsname = ['number', 'name', 'type', 'addr', 'offset', 'size', 'entsize', 'flags', 'link', 'info', 'addralign']
sec = dict(zip(fieldsname, fieldsvalue))
if sec['number'] == '0':
continue
sections.append(sec)
if sec['name'] == '.text':
textaddr = sec['addr']
return (textaddr, sections)
class AddSymbolFileAll(gdb.Command):
"""The right version for add-symbol-file"""
def __init__(self):
super(AddSymbolFileAll, self).__init__("add-symbol-file-all", gdb.COMMAND_USER)
self.dont_repeat()
def invoke(self, arg, from_tty):
argv = gdb.string_to_argv(arg)
filename = argv[0]
if len(argv) > 1:
offset = int(str(gdb.parse_and_eval(argv[1])), 0)
else:
offset = 0
(textaddr, sections) = relocatesections(filename, offset)
cmd = "add-symbol-file %s 0x%08x" % (filename, int(textaddr, 16) + offset)
for s in sections:
addr = int(s['addr'], 16)
if s['name'] == '.text' or addr == 0:
continue
cmd += " -s %s 0x%08x" % (s['name'], addr + offset)
gdb.execute(cmd)
class RemoveSymbolFileAll(gdb.Command):
"""The right version for remove-symbol-file"""
def __init__(self):
super(RemoveSymbolFileAll, self).__init__("remove-symbol-file-all", gdb.COMMAND_USER)
self.dont_repeat()
def invoke(self, arg, from_tty):
argv = gdb.string_to_argv(arg)
filename = argv[0]
if len(argv) > 1:
offset = int(str(gdb.parse_and_eval(argv[1])), 0)
else:
offset = 0
(textaddr, _) = relocatesections(filename, offset)
cmd = "remove-symbol-file -a 0x%08x" % (int(textaddr, 16) + offset)
gdb.execute(cmd)
AddSymbolFileAll()
RemoveSymbolFileAll()
end
文件中的代码。
protected override void Seed(Tpsc.EDI.EDIContext context)
{
try
{
//EDI.Seed.DoSeed(context);
}
catch (DbEntityValidationException e)
{
...
}
}