c++ - 添加 -lrt 无效时跟踪编译器错误 "undefined reference"

Question

致力于大型嵌入式 Linux 代码库/SDK“不是这里发明的”- 由 Elbonian Code Slaves 在海外发明，将各种东西钉在一起。

部分代码库是 Live555 WIS-Streamer .为了(尝试)解决与时间戳相关的问题，我插入了对 clock_gettime(CLOCK_MONOTONIC, &ts); 的几个调用，然后导致编译失败，并出现多个 undefined reference 'clock_gettime' 错误。

我以前遇到过这个问题，通过将 -lrt 添加到编译器选项以包含 librealtime 解决了这个问题，但是这一次它没有帮助。我已经进行了大量的谷歌搜索和阅读，但我看不到任何明确的答案，而且该项目的 makefile 比在网络上找到的示例复杂得多。

我需要一些帮助，要么指出我在 makefile 中犯的非常明显的错误，要么通过链回溯编译器的期望以查看我需要进行更改的地方。

这个项目是使用给定硬件的一组库交叉编译的，所以 -lrt 仍然是必需的(我发现它在以后的 gcc 库中不再需要)并且我们无法更新或轻松更改这些内容。

这是一段失败的编译器输出，非常冗长。我缩短了路径名以保持在帖子大小限制以下。

make[10]: Entering directory `/ipnc_rdk/ipnc_app/network/live/testProgs'
/ipnc_rdk/../dvsdk_ipnctools/linux-devkit//bin/arm-arago-linux-gnueabi-g++ -c -I../UsageEnvironment/include -I../groupsock/include -I../liveMedia/include -I../BasicUsageEnvironment/include -I. -O3 -v -DSOCKLEN_T=socklen_t -DNO_STRSTREAM=1 -D_LARGEFILE_SOURCE=1 -D_FILE_OFFSET_BITS=64 -Wl,--verbose -lrt -Wall -DBSD=1 testMP3Streamer.cpp
Using built-in specs.
Target: arm-arago-linux-gnueabi
Thread model: posix
gcc version 4.3.3 (GCC) 
COLLECT_GCC_OPTIONS='-c' '-I../UsageEnvironment/include' '-I../groupsock/include' '-I../liveMedia/include' '-I../BasicUsageEnvironment/include' '-I.' '-O3' '-v' '-DSOCKLEN_T=socklen_t' '-DNO_STRSTREAM=1' '-D_LARGEFILE_SOURCE=1' '-D_FILE_OFFSET_BITS=64' '-Wall' '-DBSD=1' '-shared-libgcc' '-mfloat-abi=soft'
 ../libexec/gcc/arm-arago-linux-gnueabi/4.3.3/cc1plus -quiet -v -I../UsageEnvironment/include -I../groupsock/include -I../liveMedia/include -I../BasicUsageEnvironment/include -I. -iprefix ../lib/gcc/arm-arago-linux-gnueabi/4.3.3/ -isysroot ../arm-arago-linux-gnueabi -D_GNU_SOURCE -DSOCKLEN_T=socklen_t -DNO_STRSTREAM=1 -D_LARGEFILE_SOURCE=1 -D_FILE_OFFSET_BITS=64 -DBSD=1 testMP3Streamer.cpp -quiet -dumpbase testMP3Streamer.cpp -mfloat-abi=soft -auxbase testMP3Streamer -O3 -Wall -version -o /tmp/cckqq421.s
ignoring duplicate directory "../lib/gcc/../../lib/gcc/arm-arago-linux-gnueabi/4.3.3/../../../../arm-arago-linux-gnueabi/include/c++/4.3.3"
ignoring duplicate directory "../lib/gcc/../../lib/gcc/arm-arago-linux-gnueabi/4.3.3/../../../../arm-arago-linux-gnueabi/include/c++/4.3.3/arm-arago-linux-gnueabi"
ignoring duplicate directory "../lib/gcc/../../lib/gcc/arm-arago-linux-gnueabi/4.3.3/../../../../arm-arago-linux-gnueabi/include/c++/4.3.3/backward"
ignoring nonexistent directory "../arm-arago-linux-gnueabi/usr/local/include"
ignoring duplicate directory "../lib/gcc/../../lib/gcc/arm-arago-linux-gnueabi/4.3.3/include"
ignoring duplicate directory "../lib/gcc/../../lib/gcc/arm-arago-linux-gnueabi/4.3.3/include-fixed"
ignoring duplicate directory "../lib/gcc/../../lib/gcc/arm-arago-linux-gnueabi/4.3.3/../../../../arm-arago-linux-gnueabi/include"
#include "..." search starts here:
#include <...> search starts here:
 ../UsageEnvironment/include
 ../groupsock/include
 ../liveMedia/include
 ../BasicUsageEnvironment/include
 .
 ../lib/gcc/arm-arago-linux-gnueabi/4.3.3/../../../../arm-arago-linux-gnueabi/include/c++/4.3.3
 ../lib/gcc/arm-arago-linux-gnueabi/4.3.3/../../../../arm-arago-linux-gnueabi/include/c++/4.3.3/arm-arago-linux-gnueabi
 ../lib/gcc/arm-arago-linux-gnueabi/4.3.3/../../../../arm-arago-linux-gnueabi/include/c++/4.3.3/backward
 ../lib/gcc/arm-arago-linux-gnueabi/4.3.3/include
 ../lib/gcc/arm-arago-linux-gnueabi/4.3.3/include-fixed
 ../lib/gcc/arm-arago-linux-gnueabi/4.3.3/../../../../arm-arago-linux-gnueabi/include
 ../arm-arago-linux-gnueabi/usr/include
End of search list.
GNU C++ (GCC) version 4.3.3 (arm-arago-linux-gnueabi)
    compiled by GNU C version 4.4.3, GMP version 4.2.4, MPFR version 3.0.0-p7.
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 05177eff49440274f3899a250a52b5a7
COLLECT_GCC_OPTIONS='-c' '-I../UsageEnvironment/include' '-I../groupsock/include' '-I../liveMedia/include' '-I../BasicUsageEnvironment/include' '-I.' '-O3' '-v' '-DSOCKLEN_T=socklen_t' '-DNO_STRSTREAM=1' '-D_LARGEFILE_SOURCE=1' '-D_FILE_OFFSET_BITS=64' '-Wall' '-DBSD=1' '-shared-libgcc' '-mfloat-abi=soft'
 ../lib/gcc/arm-arago-linux-gnueabi/4.3.3/../../../../arm-arago-linux-gnueabi/bin/as -mfloat-abi=soft -meabi=4 -o testMP3Streamer.o /tmp/cckqq421.s
COMPILER_PATH=../libexec/gcc/arm-arago-linux-gnueabi/4.3.3/:../libexec/gcc/:../lib/gcc/arm-arago-linux-gnueabi/4.3.3/../../../../arm-arago-linux-gnueabi/bin/
LIBRARY_PATH=../lib/gcc/arm-arago-linux-gnueabi/4.3.3/:../lib/gcc/:../lib/gcc/arm-arago-linux-gnueabi/4.3.3/../../../../arm-arago-linux-gnueabi/lib/:../arm-arago-linux-gnueabi/lib/:../arm-arago-linux-gnueabi/usr/lib/
COLLECT_GCC_OPTIONS='-c' '-I../UsageEnvironment/include' '-I../groupsock/include' '-I../liveMedia/include' '-I../BasicUsageEnvironment/include' '-I.' '-O3' '-v' '-DSOCKLEN_T=socklen_t' '-DNO_STRSTREAM=1' '-D_LARGEFILE_SOURCE=1' '-D_FILE_OFFSET_BITS=64' '-Wall' '-DBSD=1' '-shared-libgcc' '-mfloat-abi=soft'
/ipnc_rdk/../dvsdk_ipnctools/linux-devkit//bin/arm-arago-linux-gnueabi-g++ -otestMP3Streamer -L. testMP3Streamer.o ../liveMedia/libliveMedia.a ../groupsock/libgroupsock.a ../BasicUsageEnvironment/libBasicUsageEnvironment.a ../UsageEnvironment/libUsageEnvironment.a 
../liveMedia/libliveMedia.a: In function `RTPSink::presetNextTimestamp()':
Locale.cpp:(.text+0x3232c): undefined reference to `clock_gettime'
../liveMedia/libliveMedia.a: In function `RTCPInstance::addSR()':
Locale.cpp:(.text+0x36dd8): undefined reference to `clock_gettime'
../BasicUsageEnvironment/libBasicUsageEnvironment.a: In function `TimeNow()':
BasicHashTable.cpp:(.text+0x1edc): undefined reference to `clock_gettime'
../BasicUsageEnvironment/libBasicUsageEnvironment.a: In function `DelayQueue::DelayQueue()':
BasicHashTable.cpp:(.text+0x2378): undefined reference to `clock_gettime'
../BasicUsageEnvironment/libBasicUsageEnvironment.a: In function `DelayQueue::DelayQueue()':
BasicHashTable.cpp:(.text+0x2414): undefined reference to `clock_gettime'
../BasicUsageEnvironment/libBasicUsageEnvironment.a:BasicHashTable.cpp:(.text+0x246c): more undefined references to `clock_gettime' follow
collect2: ld returned 1 exit status
make[10]: *** [testMP3Streamer] Error 1

不幸的是，我无法附加 makefile 的完整输出或内容，因为我似乎已经达到了帖子长度限制!这是 makefile 的大部分内容，我已将 ...snip... 我在其中删除了很多类似的条目，您可能会猜到发生了什么:

INCLUDES = -Iinclude -I../UsageEnvironment/include -I../groupsock/include
PREFIX = /usr/local
LIBDIR = $(PREFIX)/lib
##### Change the following for your environment:
CROSS_COMPILE=      $(MVTOOL_PREFIX)
COMPILE_OPTS =      $(INCLUDES) -I. -v -Wall -O3 -DSOCKLEN_T=socklen_t -DNO_STRSTREAM=1 -D_LARGEFILE_SOURCE=1 -D_FILE_OFFSET_BITS=64 -Wl,--verbose -lrt
### JU - Added -lrt for MONOTONIC CLOCK in RTPSink.cpp
C =         c
C_COMPILER =        $(CROSS_COMPILE)gcc
C_FLAGS =       $(COMPILE_OPTS)
CPP =           cpp
CPLUSPLUS_COMPILER =    $(CROSS_COMPILE)g++
CPLUSPLUS_FLAGS =   $(COMPILE_OPTS) -DBSD=1
OBJ =           o
LINK =          $(CROSS_COMPILE)g++ -o
LINK_OPTS =     -L.
CONSOLE_LINK_OPTS = $(LINK_OPTS)
LIBRARY_LINK =      $(CROSS_COMPILE)ld -o
LIBRARY_LINK_OPTS = $(LINK_OPTS) -r -Bstatic
LIB_SUFFIX =            a
LIBS_FOR_CONSOLE_APPLICATION =
LIBS_FOR_GUI_APPLICATION =
EXE =
##### End of variables to change

NAME = libliveMedia
LIVEMEDIA_LIB = $(NAME).$(LIB_SUFFIX)
ALL = $(LIVEMEDIA_LIB)
all:    $(ALL)

.$(C).$(OBJ):
    $(C_COMPILER) -c $(C_FLAGS) $<       
.$(CPP).$(OBJ):
    $(CPLUSPLUS_COMPILER) -c $(CPLUSPLUS_FLAGS) $<

MP3_SOURCE_OBJS = MP3FileSource.$(OBJ)  ...snip...  MP3InternalsHuffman.$(OBJ) MP3InternalsHuffmanTable.$(OBJ) MP3ADURTPSource.$(OBJ)
MPEG_SOURCE_OBJS = MPEG1or2Demux.$(OBJ)  ...snip...  ADTSAudioFileSource.$(OBJ)
H263_SOURCE_OBJS = H263plusVideoRTPSource.$(OBJ) H263plusVideoStreamFramer.$(OBJ) H263plusVideoStreamParser.$(OBJ)
AC3_SOURCE_OBJS = AC3AudioStreamFramer.$(OBJ) AC3AudioRTPSource.$(OBJ)
DV_SOURCE_OBJS = DVVideoStreamFramer.$(OBJ) DVVideoRTPSource.$(OBJ)
MP3_SINK_OBJS = MP3ADURTPSink.$(OBJ)
MPEG_SINK_OBJS = MPEG1or2AudioRTPSink.$(OBJ) $(MP3_SINK_OBJS) MPEG1or2VideoRTPSink.$(OBJ) MPEG4LATMAudioRTPSink.$(OBJ) MPEG4GenericRTPSink.$(OBJ) MPEG4ESVideoRTPSink.$(OBJ)
H263_SINK_OBJS = H263plusVideoRTPSink.$(OBJ)
H264_OR_5_SINK_OBJS = H264or5VideoRTPSink.$(OBJ) H264VideoRTPSink.$(OBJ) H265VideoRTPSink.$(OBJ)
DV_SINK_OBJS = DVVideoRTPSink.$(OBJ)
AC3_SINK_OBJS = AC3AudioRTPSink.$(OBJ)

MISC_SOURCE_OBJS = MediaSource.$(OBJ)  ...snip... StreamReplicator.$(OBJ)
MISC_SINK_OBJS = MediaSink.$(OBJ)  ...snip...  OutputFile.$(OBJ)
MISC_FILTER_OBJS = uLawAudioFilter.$(OBJ)
TRANSPORT_STREAM_TRICK_PLAY_OBJS = MPEG2IndexFromTransportStream.$(OBJ) MPEG2TransportStreamIndexFile.$(OBJ) MPEG2TransportStreamTrickModeFilter.$(OBJ)

RTP_SOURCE_OBJS = RTPSource.$(OBJ)  ...snip...  VP9VideoRTPSource.$(OBJ)
RTP_SINK_OBJS = RTPSink.$(OBJ) MultiFramedRTPSink.$(OBJ) AudioRTPSink.$(OBJ) VideoRTPSink.$(OBJ) TextRTPSink.$(OBJ)
RTP_INTERFACE_OBJS = RTPInterface.$(OBJ)
RTP_OBJS = $(RTP_SOURCE_OBJS) $(RTP_SINK_OBJS) $(RTP_INTERFACE_OBJS)

RTCP_OBJS = RTCP.$(OBJ) rtcp_from_spec.$(OBJ)
GENERIC_MEDIA_SERVER_OBJS = GenericMediaServer.$(OBJ)
RTSP_OBJS = RTSPServer.$(OBJ) RTSPClient.$(OBJ) RTSPCommon.$(OBJ) RTSPServerSupportingHTTPStreaming.$(OBJ) RTSPRegisterSender.$(OBJ)
SIP_OBJS = SIPClient.$(OBJ)

SESSION_OBJS = MediaSession.$(OBJ)  ...snip...  ProxyServerMediaSession.$(OBJ)

QUICKTIME_OBJS = QuickTimeFileSink.$(OBJ) QuickTimeGenericRTPSource.$(OBJ)
AVI_OBJS = AVIFileSink.$(OBJ)

MATROSKA_FILE_OBJS = MatroskaFile.$(OBJ) MatroskaFileParser.$(OBJ) EBMLNumber.$(OBJ) MatroskaDemuxedTrack.$(OBJ)
MATROSKA_SERVER_MEDIA_SUBSESSION_OBJS = MatroskaFileServerMediaSubsession.$(OBJ) MP3AudioMatroskaFileServerMediaSubsession.$(OBJ)
MATROSKA_RTSP_SERVER_OBJS = MatroskaFileServerDemux.$(OBJ) $(MATROSKA_SERVER_MEDIA_SUBSESSION_OBJS)
MATROSKA_OBJS = $(MATROSKA_FILE_OBJS) $(MATROSKA_RTSP_SERVER_OBJS)

OGG_FILE_OBJS = OggFile.$(OBJ) OggFileParser.$(OBJ) OggDemuxedTrack.$(OBJ)
OGG_SERVER_MEDIA_SUBSESSION_OBJS = OggFileServerMediaSubsession.$(OBJ)
OGG_RTSP_SERVER_OBJS = OggFileServerDemux.$(OBJ) $(OGG_SERVER_MEDIA_SUBSESSION_OBJS)
OGG_OBJS = $(OGG_FILE_OBJS) $(OGG_RTSP_SERVER_OBJS)

MISC_OBJS = BitVector.$(OBJ) StreamParser.$(OBJ) DigestAuthentication.$(OBJ) ourMD5.$(OBJ) Base64.$(OBJ) Locale.$(OBJ)

LIVEMEDIA_LIB_OBJS = Media.$(OBJ) $(MISC_SOURCE_OBJS) $(MISC_SINK_OBJS) $(MISC_FILTER_OBJS) $(RTP_OBJS) $(RTCP_OBJS) $(GENERIC_MEDIA_SERVER_OBJS) $(RTSP_OBJS) $(SIP_OBJS) $(SESSION_OBJS) $(QUICKTIME_OBJS) $(AVI_OBJS) $(TRANSPORT_STREAM_TRICK_PLAY_OBJS) $(MATROSKA_OBJS) $(OGG_OBJS) $(MISC_OBJS)

$(LIVEMEDIA_LIB): $(LIVEMEDIA_LIB_OBJS) \
    $(PLATFORM_SPECIFIC_LIB_OBJS)
    $(LIBRARY_LINK)$@ $(LIBRARY_LINK_OPTS) \
        $(LIVEMEDIA_LIB_OBJS)

Media.$(CPP):       include/Media.hh
include/Media.hh:   include/liveMedia_version.hh
MediaSource.$(CPP): include/MediaSource.hh
include/MediaSource.hh:     include/Media.hh
FramedSource.$(CPP):    include/FramedSource.hh
include/FramedSource.hh:    include/MediaSource.hh

 ...snip... 

ourMD5.$(CPP):  include/ourMD5.hh
Base64.$(CPP):  include/Base64.hh
Locale.$(CPP):  include/Locale.hh

include/liveMedia.hh:: include/MPEG1or2AudioRTPSink.hh  ...snip...  include/VP9VideoRTPSource.hh

include/liveMedia.hh::  include/MPEG2TransportStreamFromPESSource.hh  ...snip...  include/RTSPRegisterSender.hh

include/liveMedia.hh:: include/RTSPServerSupportingHTTPStreaming.hh ...snip... include/ProxyServerMediaSession.hh

clean:
    -rm -rf *.$(OBJ) $(ALL) core *.core *~ include/*~

install: install1 $(INSTALL2)
install1: $(LIVEMEDIA_LIB)
     install -d $(DESTDIR)$(PREFIX)/include/liveMedia $(DESTDIR)$(LIBDIR)
     install -m 644 include/*.hh $(DESTDIR)$(PREFIX)/include/liveMedia
     install -m 644 $(LIVEMEDIA_LIB) $(DESTDIR)$(LIBDIR)
install_shared_libraries: $(LIVEMEDIA_LIB)
     ln -fs $(NAME).$(LIB_SUFFIX) $(DESTDIR)$(LIBDIR)/$(NAME).$(SHORT_LIB_SUFFIX)
     ln -fs $(NAME).$(LIB_SUFFIX) $(DESTDIR)$(LIBDIR)/$(NAME).so

##### Any additional, platform-specific rules come here:

Answer 1

您已经添加了 -lrt - 显然还有 -Wl,--verbose - 到COMPILE_OPTS 的定义。那是行不通的，因为 $(COMPILE_OPTS)仅传递给编译器的调用，-lrt 是一个链接器选项，您必须将其传递给链接器的调用，因为它有任何效果。

从 COMPILE_OPTS 的定义中删除 -lrt 并将其添加到LIBRARY_LINK_OPTS 的定义。

(这同样适用于 -Wl,--verbose，尽管您可能只引入它进行调试。你明明知道-Wl,option的意思将选项传递给链接器。但这条指令是针对gcc/g++ 工具驱动程序，在调用链接器时有效，不是在调用编译器时。因此你有详细的编译器输出，由于 -v` 选项，但没有详细的链接器输出)。