Logo Questions Linux Laravel Mysql Ubuntu Git Menu
 

What library does ld option -lrt refer to (Bionic libc)?

What does this option to ld mean?

-lrt

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.

With Bionic (android) libc, the android NDK docs detail that this (along with pthreads) has been integrated.

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)

EDIT

From the Bionic Overview

Bionic's C library comes with its own pthread implementation bundled in. This is different from other historical C libraries which:

- place it in an external library (-lpthread) - play linker tricks with weak symbols at dynamic link time 

The support for real-time features (a.k.a. -lrt) is also bundled in the C library.

The problem is that collect2 is passing the option -lrt (and also -lpthreads) to ld.

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 

Is there a way to override this behavior?

like image 754
dwerner Avatar asked Jul 19 '11 20:07

dwerner


People also ask

What is Ubuntu ld?

ld combines a number of object and archive files, relocates their data and ties up symbol references. Usually the last step in compiling a program is to run ld.

What is LIBC Android?

libc++ LLVM's libc++ is the C++ standard library that has been used by the Android OS since Lollipop, and as of NDK r18 is the only STL available in the NDK. Note: For full details of the expected level of C++ library support for any given version, see the C++14 Status, C++17 Status, and C++20 Status pages.

What does usr bin ld Cannot find?

A message such as /usr/bin/ld: cannot find -linput actually means it was looking for a file named libinput.so . The -l flag is a command-line argument (to ld or to gcc ) that expects the library name to follow and then the library name is used to form the file name which includes the lib prefix and the .

Is LIBC automatically linked?

libc is always searched automatically.


1 Answers

When you see a -lsomething, the library name is libsomething. Doing a man librt says the following:

NAME      librt, libposix4 - POSIX.1b Realtime Extensions library  SYNOPSIS      cc [ flag... ] file... -lrt [ library... ]  DESCRIPTION      Functions in this library provide  most  of  the  interfaces      specified  by  the  POSIX.1b  Realtime Extension.  See stan-      dards(5). Specifically, this includes the interfaces defined      under   the   Asynchronous  I/O,  Message  Passing,  Process      Scheduling, Realtime Signals Extension,  Semaphores,  Shared      Memory  Objects,  Synchronized  I/O, and Timers options. The      interfaces defined under the Memory  Mapped  Files,  Process      Memory  Locking,  and  Range Memory Locking options are pro-      vided in libc(3LIB)       See the man pages for the individual interfaces  in  section      3RT for information on required headers.       The name libposix4 is maintained for backward  compatibility      and  should be avoided. librt is the preferred name for this      library. 
like image 141
Chris Eberle Avatar answered Sep 25 '22 00:09

Chris Eberle