title: What library does ld option -lrt refer to (Bionic libc)?
body: <p>What does this option to ld mean?</p>
  
  <p><code>-lrt</code></p>
  
  <p>I know to some degree it means that ld is looking for the library with real-time extensions, but after searching extensively, I couldn't find an exact definition (or which library) this is referring to.</p>
  
  <p>With Bionic (android) libc, the android NDK docs detail that this (along with pthreads) has been integrated. </p>
  
  <p>I ask because it seems to be implicit (ie when I invoke the compiler, a custom-compiled gdc, directly, I get a message saying that ld cannot find -lrt)</p>
  
  <p>EDIT</p>
  
  <p>From the Bionic Overview</p>
  
  <blockquote>
    <p>Bionic's C library comes with its own pthread implementation bundled
    in.    This is different from other historical C libraries which:</p>
  
  <pre><code>- place it in an external library (-lpthread)
  - play linker tricks with weak symbols at dynamic link time
  </code></pre>
    
    <p>The support for real-time features (a.k.a. -lrt) is also bundled in
    the    C library.</p>
  </blockquote>
  
  <p>The problem is that collect2 is passing the option -lrt (and also -lpthreads) to ld.</p>
  
  <pre><code>dan@devbox:~/projects/gdc_test/jni/src$ $DC gdc_test.d -v -mthumb
  Using built-in specs.
  Target: arm-linux-androideabi
  Configured with: /arm/ndk-git/src/build/../gcc/gcc-4.4.3/configure --prefix=/arm/ndk-git/ndk/toolchains/arm-linux-androideabi-4.4.3/prebuilt/linux-x86 --target=arm-linux-androideabi --host=x86_64-linux-gnu --build=x86_64-linux-gnu --with-gnu-as --with-gnu-ld --enable-languages=c,c++ --with-gmp=/arm/ndk-git/build_run/temp-install --with-mpfr=/arm/ndk-git/build_run/temp-install --disable-libssp --enable-threads --disable-nls --disable-libmudflap --disable-libgomp --disable-libstdc__-v3 --disable-sjlj-exceptions --disable-shared --disable-tls --enable-languages=c,d,c++ --enable-lto --with-float=soft --with-fpu=vfp --with-arch=armv5te --enable-target-optspace --enable-shared--prefix=/arm/ndk-git/ndk/toolchains/arm-linux-androideabi-4.4.3/prebuilt/linux-x86 --enable-initfini-array --disable-nls --prefix=/arm/ndk-git/ndk/toolchains/arm-linux-androideabi-4.4.3/prebuilt/linux-x86 --with-sysroot=/arm/ndk-git/ndk/toolchains/arm-linux-androideabi-4.4.3/prebuilt/linux-x86/sysroot --with-binutils-version=2.19 --with-mpfr-version=2.4.1 --with-gmp-version=4.2.4 --with-gcc-version=4.4.3 --with-gdb-version=6.6 --with-arch=armv5te --enable-libstdc__-v3 --disable-werrors --enable-languages=c,d,c++ --enable-shared --enable-multilib --disable-threads --program-transform-name='s,^,arm-linux-androideabi-,'
  Thread model: single
  gcc version 4.4.3 20100121 (gdc hg, using dmd 1.067) (GCC) 
  COLLECT_GCC_OPTIONS='-v' '-mthumb' '-shared-libgcc' '-pthread' '-march=armv5te' '-mfloat-abi=soft' '-mfpu=vfp'
   /home/dan/projects/arm-linux-androideabi-4.4.3/bin/../libexec/gcc/arm-linux-androideabi/4.4.3/cc1d gdc_test.d -mbionic -fpic -quiet -dumpbase gdc_test.d -mthumb -march=armv5te -mfloat-abi=soft -mfpu=vfp -auxbase gdc_test -version -imultilib thumb -iprefix /home/dan/projects/arm-linux-androideabi-4.4.3/bin/../lib/gcc/arm-linux-androideabi/4.4.3/ -isysroot /home/dan/projects/arm-linux-androideabi-4.4.3/bin/../sysroot -fmultilib-dir=thumb -o /tmp/cc2yu97y.s
  GNU D (GCC) version 4.4.3 20100121 (gdc hg, using dmd 1.067) (arm-linux-androideabi)
      compiled by GNU C version 4.5.2, GMP version 4.2.4, MPFR version 2.4.1.
  GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
  GNU D (GCC) version 4.4.3 20100121 (gdc hg, using dmd 1.067) (arm-linux-androideabi)
      compiled by GNU C version 4.5.2, GMP version 4.2.4, MPFR version 2.4.1.
  GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
  COLLECT_GCC_OPTIONS='-v' '-mthumb' '-shared-libgcc' '-pthread' '-march=armv5te' '-mfloat-abi=soft' '-mfpu=vfp'
   /home/dan/projects/arm-linux-androideabi-4.4.3/bin/../lib/gcc/arm-linux-androideabi/4.4.3/../../../../arm-linux-androideabi/bin/as -v -march=armv5te -mfloat-abi=soft -mfpu=vfp -meabi=5 -o /tmp/ccuFGEfj.o /tmp/cc2yu97y.s
  GNU assembler version 2.19 (arm-linux-androideabi) using BFD version (GNU Binutils) 2.19
  COMPILER_PATH=/home/dan/projects/arm-linux-androideabi-4.4.3/bin/../libexec/gcc/arm-linux-androideabi/4.4.3/:/home/dan/projects/arm-linux-androideabi-4.4.3/bin/../libexec/gcc/:/home/dan/projects/arm-linux-androideabi-4.4.3/bin/../lib/gcc/arm-linux-androideabi/4.4.3/../../../../arm-linux-androideabi/bin/
  LIBRARY_PATH=/home/dan/projects/arm-linux-androideabi-4.4.3/bin/../lib/gcc/arm-linux-androideabi/4.4.3/thumb/:/home/dan/projects/arm-linux-androideabi-4.4.3/bin/../lib/gcc/arm-linux-androideabi/4.4.3/../../../../arm-linux-androideabi/lib/thumb/:/home/dan/projects/arm-linux-androideabi-4.4.3/bin/../lib/gcc/arm-linux-androideabi/4.4.3/:/home/dan/projects/arm-linux-androideabi-4.4.3/bin/../lib/gcc/:/home/dan/projects/arm-linux-androideabi-4.4.3/bin/../lib/gcc/arm-linux-androideabi/4.4.3/../../../../arm-linux-androideabi/lib/:/home/dan/projects/arm-linux-androideabi-4.4.3/bin/../sysroot/usr/lib/
  COLLECT_GCC_OPTIONS='-v' '-mthumb' '-shared-libgcc' '-pthread' '-march=armv5te' '-mfloat-abi=soft' '-mfpu=vfp'
   /home/dan/projects/arm-linux-androideabi-4.4.3/bin/../libexec/gcc/arm-linux-androideabi/4.4.3/collect2 --sysroot=/home/dan/projects/arm-linux-androideabi-4.4.3/bin/../sysroot --eh-frame-hdr -dynamic-linker /system/bin/linker -X -m armelf_linux_eabi /home/dan/projects/arm-linux-androideabi-4.4.3/bin/../sysroot/usr/lib/crtbegin_dynamic.o -L/home/dan/projects/arm-linux-androideabi-4.4.3/bin/../lib/gcc/arm-linux-androideabi/4.4.3/thumb -L/home/dan/projects/arm-linux-androideabi-4.4.3/bin/../lib/gcc/arm-linux-androideabi/4.4.3/../../../../arm-linux-androideabi/lib/thumb -L/home/dan/projects/arm-linux-androideabi-4.4.3/bin/../lib/gcc/arm-linux-androideabi/4.4.3 -L/home/dan/projects/arm-linux-androideabi-4.4.3/bin/../lib/gcc -L/home/dan/projects/arm-linux-androideabi-4.4.3/bin/../lib/gcc/arm-linux-androideabi/4.4.3/../../../../arm-linux-androideabi/lib -L/home/dan/projects/arm-linux-androideabi-4.4.3/bin/../sysroot/usr/lib /tmp/ccuFGEfj.o -lgphobos -lm -lrt -lgcc_s -lgcc -lpthread -lc -ldl -lgcc_s -lgcc /home/dan/projects/arm-linux-androideabi-4.4.3/bin/../sysroot/usr/lib/crtend_android.o
  /home/dan/projects/arm-linux-androideabi-4.4.3/bin/../lib/gcc/arm-linux-androideabi/4.4.3/../../../../arm-linux-androideabi/bin/ld: cannot find -lrt
  collect2: ld returned 1 exit status
  </code></pre>
  
  <p>Is there a way to override this behavior?</p>