[SOLVED] What is a random library?

littlebigman · 06-30-2011, 08:00 AM

Hello

Since I read that executing a library could return its version number, I ran "/lib/libc.so.0" on uClinux, but it triggers an error.

I'm told that random libraries are not directly executable. Does someone know what a random library is?

Thank you.

PS: In case that matters, here's the short version of the error:

Code:

Undefined instruction
<5> - May be used to emulate instructions that are not defined for
<5>   a particular processor implementation.
Deferred Exception context
CURRENT PROCESS:
COMM=libc.so.0 PID=70  CPU=0
TEXT = 0x02200000-0x0223a6f4        DATA = 0x025586f4-0x0255c3f4
 BSS = 0x0255c3f4-0x02560000  USER-STACK = 0x0257fe90

SEQUENCER STATUS:               Not tainted
 SEQSTAT: 00062021  IPEND: 0008  IMASK: ffff  SYSCFG: 0006
  EXCAUSE   : 0x21
  physical IVG3 asserted : <0xffa08720> { _trap + 0x0 }
 RETE: <0x00000000> /* Maybe null pointer? */
 RETN: <0x02330000> [ /bin/inetd + 0x0 ]
 RETX: <0x00000480> /* Maybe fixed code section */
 RETS: <0x020f0cb0> [ /lib/ld-uClibc.so.0 + 0xcb0 ]
 PC  : <0x02580002> /* kernel dynamic memory */
DCPLB_FAULT_ADDR: <0x0257feac> [ libc.so.0 + 0x1feac ]
ICPLB_FAULT_ADDR: <0x02580002> /* kernel dynamic memory */

Hardware Trace:
   0 Target : <0x00003e30> { _trap_c + 0x0 }
     Source : <0xffa086b4> { _exception_to_level5 + 0xa0 } CALL pcrel
   1 Target : <0xffa08614> { _exception_to_level5 + 0x0 }
     Source : <0xffa084d6> { _bfin_return_from_exception + 0x6 } RTX
   2 Target : <0xffa084d0> { _bfin_return_from_exception + 0x0 }
     Source : <0xffa0856c> { _ex_trap_c + 0x74 } JUMP.S
   3 Target : <0xffa084f8> { _ex_trap_c + 0x0 }
     Source : <0xffa08758> { _trap + 0x38 } JUMP (P4)
   4 Target : <0xffa0873e> { _trap + 0x1e }
     Source : <0xffa0873a> { _trap + 0x1a } IF CC JUMP pcrel
   5 Target : <0xffa08720> { _trap + 0x0 }
      FAULT : <0x02580002> /* kernel dynamic memory */ 0x464c
     Source : <0x02580000> /* kernel dynamic memory */ 0x457f
   6 Target : <0x0257ffce> [ libc.so.0 + 0x1ffce ]
     Source : <0x020f0cbc> [ /lib/ld-uClibc.so.0 + 0xcbc ] JUMP (P4)
   7 Target : <0x020f0cb0> [ /lib/ld-uClibc.so.0 + 0xcb0 ]
     Source : <0x0220cabc> [ /lib/libc.so.0 + 0xcabc ] RTS
   8 Target : <0x0220ca24> [ /lib/libc.so.0 + 0xca24 ]
     Source : <0x020f0cbc> [ /lib/ld-uClibc.so.0 + 0xcbc ] JUMP (P4)
   9 Target : <0x020f0cb0> [ /lib/ld-uClibc.so.0 + 0xcb0 ]
     Source : <0x020f44ce> [ /lib/ld-uClibc.so.0 + 0x44ce ] RTS
  10 Target : <0x020f44bc> [ /lib/ld-uClibc.so.0 + 0x44bc ]
     Source : <0x020f44b6> [ /lib/ld-uClibc.so.0 + 0x44b6 ] JUMP.S
  11 Target : <0x020f44a4> [ /lib/ld-uClibc.so.0 + 0x44a4 ]
     Source : <0x020f41fe> [ /lib/ld-uClibc.so.0 + 0x41fe ] RTS
  12 Target : <0x020f41f4> [ /lib/ld-uClibc.so.0 + 0x41f4 ]
     Source : <0x020f1174> [ /lib/ld-uClibc.so.0 + 0x1174 ] RTS
  13 Target : <0x020f1168> [ /lib/ld-uClibc.so.0 + 0x1168 ]
     Source : <0x020f41f0> [ /lib/ld-uClibc.so.0 + 0x41f0 ] CALL pcrel
  14 Target : <0x020f41e0> [ /lib/ld-uClibc.so.0 + 0x41e0 ]
     Source : <0x020f1ece> [ /lib/ld-uClibc.so.0 + 0x1ece ] RTS
  15 Target : <0x020f1eb6> [ /lib/ld-uClibc.so.0 + 0x1eb6 ]
     Source : <0x020f1cba> [ /lib/ld-uClibc.so.0 + 0x1cba ] RTS

Return addresses in stack:
   frame  1 : <0x00020000> { _sys_clock_gettime + 0x80 }
    address : <0x00020000> { _sys_clock_gettime + 0x80 }
ILL

fbianconi · 06-30-2011, 08:23 AM

In that context means not any library is executable.
Programs are kind of a different thing than libraries. They're both containers of executable code, but the main difference is a program has a defined starting point. A shared library (*.so) it's also an elf but an entry point must be defined in order to make it executable, and this is not a requirement for libraries, since it's main function is to be linked from another program.

littlebigman · 07-01-2011, 10:23 AM

Thanks for the info.