bug#14431: emacs 24.3 gud-gdb does not response with break command

[support]

--text follows this line--
Using M-x gud-gdb <CR> to debug an application then if I issue a command
like "b main", then gud buffer gets no response back. The gdb prompt
will only appear if I type C-c C-c. 
M-x gdb works for simple applications but have other issues when
debugging more complicated applications, thus I can not use M-x gdb too.

my gdb version is 7.6. and application is compiled with the following
gcc version:
$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-unknown-linux-gnu/4.8.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: /build/src/gcc-4.8-20130502/configure --prefix=/usr 
--libdir=/usr/lib --libexecdir=/usr/lib --mandir=/usr/share/man 
--infodir=/usr/share/info --with-bugurl=https://bugs.archlinux.org/ 
--enable-languages=c,c++,ada,fortran,go,lto,objc,obj-c++ --enable-shared 
--enable-threads=posix --with-system-zlib --enable-__cxa_atexit 
--disable-libunwind-exceptions --enable-clocale=gnu --disable-libstdcxx-pch 
--enable-gnu-unique-object --enable-linker-build-id --enable-cloog-backend=isl 
--disable-cloog-version-check --enable-lto --enable-gold --enable-ld=default 
--enable-plugin --with-plugin-ld=ld.gold --with-linker-hash-style=gnu 
--disable-install-libiberty --disable-multilib --disable-libssp 
--disable-werror --enable-checking=release
Thread model: posix
gcc version 4.8.0 20130502 (prerelease) (GCC) 





In GNU Emacs 24.3.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.8.1)
 of 2013-04-29 on eric
Windowing system distributor `The X.Org Foundation', version 11.0.11401000
Configured using:
 `configure '--prefix=/usr' '--sysconfdir=/etc' '--libexecdir=/usr/lib'
 '--localstatedir=/var' '--with-x-toolkit=gtk3' '--with-xft'
 'CFLAGS=-march=x86-64 -mtune=generic -O2 -pipe -fstack-protector
 --param=ssp-buffer-size=4'
 'LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro'
 'CPPFLAGS=-D_FORTIFY_SOURCE=2''

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t

Major mode: Debugger

Minor modes in effect:
  xterm-mouse-mode: t
  show-paren-mode: t
  tooltip-mode: t
  mouse-wheel-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  column-number-mode: t
  line-number-mode: t
  global-visual-line-mode: t
  visual-line-mode: t
  transient-mark-mode: t

Recent input:
<escape> x g u d - g d b <return> <return> b SPC m 
a i n <return> <escape> x <help-echo> <down-mouse-2> 
<mouse-2> <return>

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Loading cc-langs...done

Load-path shadows:
None found.

Features:
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