I am doing cross compile debugging. My build server CPU is amd64. My device CPU is MIPS. When I am trying to do debug the elf file compiled by myself. The gdb can only show ld.so.1
(gdb) info sharedlibrary
From To Syms Read Shared Object Library
0x7704f9c0 0x7706c490 Yes (*) /lib/ld.so.1
(*): Shared library is missing debugging information.
(gdb) q
I checked the /proc/xxxx/maps file. It showed that the shared libraries are loaded.
root@TRA:/proc/13679# cat maps
......
76549000-76d48000 rwxp 00000000 00:00 0 [stack:13682]
76d48000-76d4a000 r-xp 00000000 00:0c 5268 /usr/lib/strongswan/plugins/libstrongswan-addrblock.so
76d4a000-76d59000 ---p 00002000 00:0c 5268 /usr/lib/strongswan/plugins/libstrongswan-addrblock.so
......
If I debug the file which is installed from Debian Package server, then GDB can show all the shared libraries.
(gdb) info sharedlibrary
From To Syms Read Shared Object Library
0x77341bc0 0x77342c80 Yes (*) /lib/mips-linux-gnu/libdl.so.2
0x771d77e0 0x772ff6f0 Yes (*) /lib/mips-linux-gnu/libc.so.6
0x773549c0 0x77371490 Yes (*) /lib/ld.so.1
(*): Shared library is missing debugging information.
(gdb)
GDB version is: GNU gdb (Debian 7.7.1+dfsg-5) 7.7.1
My questions is: Why the GDB command 'info sharedlibrary' can't show all the libraries? How can I fix it?
(EDIT)
(Does every executable file need the library ld.so? It is missing.)
The output of command "mips-linux-gnu-readelf -d src/charon/.libs/charon"
Dynamic section at offset 0x1fc contains 33 entries:
Tag Type Name/Value
0x00000001 (NEEDED) Shared library: [libstrongswan.so.0]
0x00000001 (NEEDED) Shared library: [libhydra.so.0]
0x00000001 (NEEDED) Shared library: [libcharon.so.0]
0x00000001 (NEEDED) Shared library: [libm.so.6]
0x00000001 (NEEDED) Shared library: [libpthread.so.0]
0x00000001 (NEEDED) Shared library: [libdl.so.2]
0x00000001 (NEEDED) Shared library: [libc.so.6]
0x0000001d (RUNPATH) Library runpath: [/usr/lib/strongswan]
0x0000000c (INIT) 0xd00
0x0000000d (FINI) 0x2eb0
0x00000004 (HASH) 0x32c
0x00000005 (STRTAB) 0x904
0x00000006 (SYMTAB) 0x4d4
0x0000000a (STRSZ) 787 (bytes)
0x0000000b (SYMENT) 16 (bytes)
0x70000035 (MIPS_RLD_MAP_REL) 0x134dc
0x00000015 (DEBUG) 0x0
0x00000003 (PLTGOT) 0x13760
0x00000011 (REL) 0xcf0
0x00000012 (RELSZ) 16 (bytes)
0x00000013 (RELENT) 8 (bytes)
0x70000001 (MIPS_RLD_VERSION) 1
0x70000005 (MIPS_FLAGS) NOTPOT
0x70000006 (MIPS_BASE_ADDRESS) 0x0
0x7000000a (MIPS_LOCAL_GOTNO) 18
0x70000011 (MIPS_SYMTABNO) 67
0x70000012 (MIPS_UNREFEXTNO) 37
0x70000013 (MIPS_GOTSYM) 0x11
0x6ffffffb (FLAGS_1) Flags: PIE
0x6ffffffe (VERNEED) 0xca0
0x6fffffff (VERNEEDNUM) 2
0x6ffffff0 (VERSYM) 0xc18
0x00000000 (NULL) 0x0
EDIT
Debuging GDB: The gdb query ‘qXfer:libraries-svr4:read’ returned empty library list.
Breakpoint 7, svr4_current_sos_via_xfer_libraries (list=0x7fff8be59ad0, annex=<optimized out>)
at /gdb/gdb-7.11.1/gdb/solib-svr4.c:1301
1301 result = svr4_ parse_libraries (svr4_library_document, list);
1: svr4_library_document = 0x15cd9c0 "<library-list-svr4 version=\"1.0\"/>"
(gdb)
For Debian packages which are not compiled by me, the gdb query ‘qXfer:libraries-svr4:read’ returned full shared library list.
How does gdbserver construct the reply of this query ‘qXfer:libraries-svr4:read’?
EDIT
One more clue:
The pkgs installed from debian Jessie distribute is not PIE code. The code I compiled is PIE code.
root@TRA:/proc/14956# readelf -r /usr/lib/strongswan/charon
Relocation section '.rel.dyn' at offset 0xcf0 contains 2 entries:
Offset Info Type Sym.Value Sym. Name
00000000 00000000 R_MIPS_NONE
00013870 00000003 R_MIPS_REL32
root@TRA:/proc/14956# readelf -r /usr/bin/id
There are no relocations in this file.
root@TRA:/proc/14956#
EDIT
After debugging gdbserver, I found one strange info. The DT_DEBUG entry of the running proc is 0. After loader relocate the code, the DT_DEBUG should not be 0.(?) Does the system not support PIE code? I am using Debian Jessie MIPS system.
gdbserver source code:
if (dyn->d_tag == DT_DEBUG && map == -1)
map = dyn->d_un.d_val;
gdbserver dbg print
(gdb) p *dyn
$19 = {d_tag = 21, d_un = {d_val = 0, d_ptr = 0}}
(gdb)
EDIT
Get some information from this link: https://sourceware.org/ml/binutils/2015-06/msg00166.html
I installed gdbserver from Debian Jessie mips-pkg server. But it seems not support PIE. Where can I install the mips-gdbserver which can support PIE?
Or how can I disable the gcc compiler generate PIE code? I tried these flags (-fno-pie -fPIC) in cross-compile, but it still generate PIE code.
libtool: link: mips-linux-gnu-gcc -mfp32 -fno-pie -fPIC
-ggdb -O0 -Wall -Wno-format -Wno-format-security
-Wno-pointer-sign -I/cross-mips/usr/include -I/cross-mips/usr/include/libnl3
-I/cross-mips/usr/include/mips-linux-gnu
-I/work/strongswan/src/util
-include /work/strongswan/config.h
-o .libs/charon charon.o -L/cross-mips/lib/mips-linux-gnu
- L/cross-mips -L/cross-mips/usr/lib/mips-linux-gnu
../../src/libstrongswan/.libs/libstrongswan.so
-lm -lpthread -ldl -Wl,-rpath -Wl,/usr/lib/strongswan
Check the generated code:
mips-linux-gnu-readelf -r src/charon/.libs/charon
Relocation section '.rel.dyn' at offset 0xcf0 contains 2 entries:
Offset Info Type Sym.Value Sym. Name
00000000 00000000 R_MIPS_NONE
00013870 00000003 R_MIPS_REL32
Solution Unfortunately the reason is my compiler gcc-6 is brocken. I used 'gcc version 6.3.0 20170516 (Debian 6.3.0-18)'. It is configured with '--enable-default-pie'. And there is no way to disable PIE. And this PIE breaks static library links. I have to change my compiler to gcc5.
info sharedcommand? – Employed Russian