How to find EH_FRAME-CodePudding

Suppose I wanted a program written in C read its own eh_frame, in order to get information required for stack unwinding and exception handling. How to find out where it begins?

CodePudding user response：

You could use (like RefPerSys and GCC do) Ian Lance Taylor's libbacktrace for that purpose.

(but you'll better compile your C code with DWARF debug information, so g -Wall -g -O ...)

CodePudding user response：

Suppose I wanted a program written in C read its own eh_frame

The .eh_frame_hdr is linked into its own GNU_EH_FRAME program header, precisely so it's easy for runtime libraries to locate .eh_frame at runtime.

Here is a typical layout:

readelf -Wl /bin/date

Elf file type is DYN (Position-Independent Executable file)
Entry point 0x3cd0
There are 11 program headers, starting at offset 64

Program Headers:
  Type           Offset   VirtAddr           PhysAddr           FileSiz  MemSiz   Flg Align
  PHDR           0x000040 0x0000000000000040 0x0000000000000040 0x000268 0x000268 R   0x8
  INTERP         0x0002a8 0x00000000000002a8 0x00000000000002a8 0x00001c 0x00001c R   0x1
      [Requesting program interpreter: /lib64/ld-linux-x86-64.so.2]
  LOAD           0x000000 0x0000000000000000 0x0000000000000000 0x002790 0x002790 R   0x1000
  LOAD           0x003000 0x0000000000003000 0x0000000000003000 0x010139 0x010139 R E 0x1000
  LOAD           0x014000 0x0000000000014000 0x0000000000014000 0x005ad8 0x005ad8 R   0x1000
  LOAD           0x01a250 0x000000000001b250 0x000000000001b250 0x001090 0x001248 RW  0x1000
  DYNAMIC        0x01adf8 0x000000000001bdf8 0x000000000001bdf8 0x0001e0 0x0001e0 RW  0x8
  NOTE           0x0002c4 0x00000000000002c4 0x00000000000002c4 0x000044 0x000044 R   0x4
  GNU_EH_FRAME   0x017fe0 0x0000000000017fe0 0x0000000000017fe0 0x00040c 0x00040c R   0x4
  GNU_STACK      0x000000 0x0000000000000000 0x0000000000000000 0x000000 0x000000 RW  0x10
  GNU_RELRO      0x01a250 0x000000000001b250 0x000000000001b250 0x000db0 0x000db0 R   0x1

 Section to Segment mapping:
  Segment Sections...
   00
   01     .interp
   02     .interp .note.gnu.build-id .note.ABI-tag .gnu.hash .dynsym .dynstr .gnu.version .gnu.version_r .rela.dyn .rela.plt
   03     .init .plt .plt.got .text .fini
   04     .rodata .eh_frame_hdr .eh_frame
   05     .init_array .fini_array .data.rel.ro .dynamic .got .got.plt .data .bss
   06     .dynamic
   07     .note.gnu.build-id .note.ABI-tag
   08     .eh_frame_hdr
   09
   10     .init_array .fini_array .data.rel.ro .dynamic .got

So start with GNU_EH_FRAME segment, and follow the links.