> Remembered another issue: thread-local storage (TLS) with shared libraries. > Windows PE doesn't support TLS via special sections, so compilers use TLS > emulation layer. With static libraries, there are no issues described below. > > The first aspect is a build-time issue of MinGW. When linking to DPDK shared > libraries, errors occur: > > undefined reference to `__emutls_v.per_lcore__rte_errno' > undefined reference to `__emutls_v.per_lcore__rte_lcore_id' > > DPDK declares per_lcore__XXX in a map file, but GCC places __thread symbols > in __emutls_v section, so the proper name to export becomes __emutls_v.XXX. > This can be worked around by using an additional version script with MinGW, > as I do in my port [0], however, the proper solution would be fixing the bug > on MinGW side [1]. MinGW already converts TLS variable names when generating > DEF files with `-Wl,--output-def` option (not used by DPDK, just a hint).
Did some research and AFAICT, there is not effortless solution for efficient per-lcore variables on Windows. While MinGW-w64 has aforementioned issues (actually, GCC on Windows does), Clang with default TLS options just generates wrong results when exporting variables from dynamic libraries. Demo: https://github.com/PlushBeaver/tlstest Thread [0] claims this is a fundamental problem with PE-COFF executable format, but I honestly lack expertise to tell if this is valid. Microsoft docs [1] suggests that exporting __thread variables won't just work. Can someone from Microsoft or from UNH Lab comment further? [0]: https://sourceforge.net/p/mingw-w64/mailman/message/31777672/ [1]: https://docs.microsoft.com/en-us/windows/win32/dlls/using-thread-local-storage-in-a-dynamic-link-library -- Dmitry Kozlyuk
