[cfe-dev] Non-PIC code causes ld --shared to fail when using -fsanitize=undefined in trunk but not 3.4.

[Prof Brian Ripley]

It is not clear to me which list covers use of this flag, but as it 
appears to this user as a compiler bug, I am posting here.  Please tell 
me where is the correct place if this is not it.

We use clang to run UBSAN over code for the R project, which makes 
extensive use of DSOs to dynamically load extensions.  This works fine 
with 3.4, but not with the trunk.

For an empty file test.c, trunk gives

clang -fsanitize=undefined -fpic -g -O2 -mtune=native -c test.c -o test.o
clang -fsanitize=undefined -shared -o test.so test.o
/usr/bin/ld: 
/usr/local/clang3.5t/bin/../lib/clang/3.5.0/lib/linux/libclang_rt.san-x86_64.a(sanitizer_tls_get_addr.o): 
relocation R_X86_64_TPOFF32 against `_ZN11__sanitizerL4dtlsE' can not be 
used when making a shared object; recompile with -fPIC
/usr/local/clang3.5t/bin/../lib/clang/3.5.0/lib/linux/libclang_rt.san-x86_64.a(sanitizer_tls_get_addr.o): 
could not read symbols: Bad value
clang: error: linker command failed with exit code 1 (use -v to see 
invocation)

whereas 3.4 successfully compiled test.so.

This is x86_64 Linux, specifically Fedora 20, and trunk compiled 
starting with clang 3.4. I first saw this around early Feb 2014, and 
some bisection shows that r200062 was the last version I tried that worked.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595