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IDProjectCategoryView StatusDate SubmittedLast Update
0002233CMakeCMakepublic2005-09-14 14:122005-11-28 15:21
ReporterMathieu Malaterre 
Assigned ToBill Hoffman 
PrioritylowSeverityminorReproducibilityalways
StatusclosedResolutionno change required 
PlatformOSOS Version
Product Version 
Target VersionFixed in Version 
Summary0002233: -fPIC flags are required to build static lib on Linux/AMD64
DescriptionI cannot build properly ITK in static lib unless I explicitely set the C/CXX flags to use -fPIC.
It would be nicer if cmake was aware of this.

OS: Linux gentoo, AMD64. gcc 3.4.4
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(0003022)
Mathieu Malaterre (developer)
2005-09-14 14:49

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Shared libraries must be compiled with -fPIC.

i386 and other ports tolerate shared libraries that are not compiled
with -fPIC. On x86-64 this leads to a crash when accessing external
symbols to the shared library (e.g. symbols declared in the main
program) because only 32bit relocations are used for referencing
them. The shared library is loaded more than 32bits away from the main
program. The 32bit relocations sometimes work between shared libraries
when they are loaded at startup because then the shared libraries are
within reach of 32bit, but it may fail for shared libraries that are
loaded later with dlopen() for example.

How to check:
Run readelf -r and nm on the shared library. Relocations showing as 'U'
in nm must have an corresponding entry in the GOT table shown as the
'.rela.got'.

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http://www.x86-64.org/lists/discuss/msg02621.html [^]
(0003026)
Bill Hoffman (manager)
2005-09-15 13:23

 I don't understand why building itk static would be a problem with shared libraries?
(0003027)
Mathieu Malaterre (developer)
2005-09-15 13:46

 Steps to reproduce:
1. Build ITK with static lib (don't change default cmake values)

2. Build InsightApplications shared libs on:

Linking CXX shared library ITKFilterLib/libExample_ITKFilterLib.so
/usr/lib/gcc/x86_64-pc-linux-gnu/3.4.4/../../../../x86_64-pc-linux-gnu/bin/ld: /home/mathieu/Dashboards/MyTests/Insight-static/bin/libITKCommon.a(itkDataObject.o): relocation R_X86_64_32 against `a local symbol' can not be used when making a shared object; recompile with -fPIC
/home/mathieu/Dashboards/MyTests/Insight-static/bin/libITKCommon.a: could not read symbols: Bad value
collect2: ld returned 1 exit status
make[2]: *** [ITKFilterLib/libExample_ITKFilterLib.so] Error 1
make[1]: *** [ITKFilterLib/Example_ITKFilterLib.dir/all] Error 2
make: *** [all] Error 2


You need to build ITK in static lib but have to explicitely specify -fPIC for CFLAGS/CXXFLAGS. A simple TRY_COMPILE can find out if -fPIC is needed.
(0003049)
Bill Hoffman (manager)
2005-09-23 15:25

 In general is not valid to link shared libraries to static ones. This would also have a problem on SUN where PIC is required for shared libraries. I am inclined to say that ITK should have to match ITK applications in BUILD_SHARED flags. I don't think cmake should force -fPIC on all projects as people using only static stuff will not want it.

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