__json_c_strerror incompatibility with link-time optimization

[lhunath]

When enabling -flto, the __json_c_strerror symbol appears to exhibit issues. I'm not sure I fully understand the error, though.

  CCLD     test_util_file
  CCLD     test_float
  CCLD     test1
  CCLD     test2
ld: reference to symbol (which has not been assigned an address) __json_c_strerror in '_json_c_get_random_seed' from /tmp/lto.o for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make[2]: *** [test1] Error 1
make[2]: *** Waiting for unfinished jobs....

[hawicz]

Maybe try a "make V=1 check" to see what command it's actually running, then check that the libjson-c it's linking in is the correct one, with that symbol present.

[lhunath]

libtool: link: gcc -arch x86_64 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.12.sdk -mmacosx-version-min=10.8 -O2 -g -flto -Wall -Werror -Wcast-qual -Wno-error=deprecated-declarations -Wextra -Wno-unused-parameter -D_GNU_SOURCE -D_REENTRANT -arch x86_64 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.12.sdk -mmacosx-version-min=10.8 -flto -o test2 test2.o  ../.libs/libjson-c.a

Relevant output of nm -m .libs/libjson-c.a:

random_seed.o:
                 (undefined) external ___error
                 (undefined) external ___stderrp
                 (undefined) external __json_c_strerror
                 (undefined) external _close
                 (undefined) external _exit
                 (undefined) external _fprintf
---------------- (LTO,CODE) external _json_c_get_random_seed
                 (undefined) external _open
                 (undefined) external _read
                 (undefined) external _stat$INODE64
                 (undefined) external _time

strerror_override.o:
---------------- (LTO,CODE) external __json_c_strerror
---------------- (LTO,DATA) external __json_c_strerror_enable
---------------- (LTO,DATA) non-external _errno_buf
---------------- (LTO,RODATA) non-external _errno_list

[hawicz]

Looks like it should be able to find it. Just a guess, but perhaps it's being picky about the order: try adjusting the Makefile.am so strerror_override.c is listed early in libjson_c_la_SOURCES, and ends up early in the .a file?

[hawicz]

I tried turning on LTO on a Debian Jessie (8) box, with gcc 4.9.2, and it worked fine there with no errors or warnings (once I hacked around some things to get it to use gcc-ar and gcc-ranlib). If there's something we can change to make this work for you, let me know and re-open this issue.