[Bug gdb/17822] New: Loading shared library is magnitude slower than run a program + dlopen/depend on the same library

["myocytebd at sina dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=17822

            Bug ID: 17822
           Summary: Loading shared library is magnitude slower than run a
                    program + dlopen/depend on the same library
           Product: gdb
           Version: 7.8
            Status: NEW
          Severity: normal
          Priority: P2
         Component: gdb
          Assignee: unassigned at sourceware dot org
          Reporter: myocytebd at sina dot com

Loading shared library is extremely slow, compared to load a program and dlopen

Platform:
Ubuntu 13.10, gdb-7.6
Ubuntu 14.10, gdb-7.8

Problem:
Use "file" command to directly load a shared library is extremely slow.
Magnitudes slower than loading a program that dlopen(), or simply depends on
the same library.

Details:
There is a (symbol-wise) light program programX, which at run-time, dlopen() a
few heavy libraries libA, libB, libC ...

1. gdb programX and run. It takes ~10 minutes to load all libraries.
2. gdb -ex "file libA" alone, takes > 1 hour, maybe infinitely. (I killed it)
(Loading individual shared library was used to generate gdb-index.)


"sudo perf top" top rankers are stable
   8.87%  libc-2.19.so                   [.] _IO_file_seekoff@@GLIBC_2.2.5
   8.85%  libc-2.19.so                   [.] __lseek_nocancel
   8.27%  [kernel]                       [k] system_call
   7.31%  libc-2.19.so                   [.] fseeko
   6.75%  libc-2.19.so                   [.] _IO_fread
   6.63%  [kernel]                       [k] system_call_after_swapgs
   6.62%  [kernel]                       [k] __fget_light
   4.39%  gdb                            [.] bfd_seek
   3.85%  [kernel]                       [k] ext4_llseek
   3.66%  gdb                            [.] _bfd_generic_get_section_contents
   3.39%  libc-2.19.so                   [.] _IO_file_xsgetn
   3.38%  [kernel]                       [k] sys_lseek
   3.07%  gdb                            [.] bfd_get_section_contents
   1.88%  gdb                            [.] bfd_bread
   1.84%  [kernel]                       [k] sysret_check
   1.84%  [kernel]                       [k] __fdget_pos
   1.68%  gdb                            [.] bfd_getl32
   1.47%  [kernel]                       [k] generic_file_llseek_size
   1.22%  libc-2.19.so                   [.] _IO_seekoff_unlocked
   0.96%  libc-2.19.so                   [.] __memcpy_sse2
   0.73%  gdb                            [.] 0x00000000002b31c0
   0.62%  libc-2.19.so                   [.] _IO_sgetn
   0.61%  libc-2.19.so                   [.] _IO_file_seek
   0.55%  [kernel]                       [k] copy_user_generic_string
   0.50%  [kernel]                       [k] system_call_fastpath

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