On Fri, 31 May 2019, Alexey Brodkin wrote: > Hi Andreas, > > I'm trying to implement multilib support for ARC port of Glibc > and for that we seem to need to have unique slibdir/rtlddir pair per > each machine flavor. In our case these are at least: > - ARC700 (legacy ARCompact architecture) > - ARC HS38 (new gen ARCv2 architecture) > - ARC HS38 with hardware floating-point > - ARC HS48 (binary-compatible with HS38 but with different pipeline so > compiler schedules instructions differently) If two processors are binary-compatible, in general you wouldn't have different library directories. (The HWCAP mechanism can be used to have a single dynamic linker search different directories for optimized libraries depending on the processor; put the relevant HWCAP bits in HWCAP_IMPORTANT. And of course you can just install different library builds depending on the processor you'll be running the resulting OS on.) Different library directories are intended for the case where binaries for different ABIs can be executed on the same system (e.g. 32-bit and 64-bit; <https://sourceware.org/ml/libc-alpha/2018-01/msg00008.html> gives more details of the various places that need updating to support such a configuration in glibc). For other cases of different ABIs, there should be different dynamic linker names, to support multiarch configurations that might run different-architecture binaries under emulation, but different library directories are not required. > Given we have in GCC a dedicated "-mcpu" value for each of items above > my first thought was to "automatically" setup slibdir/rtlddir > based on "-mcpu" value passed in CC during configuration. Checking -mcpu in CC is a bad idea, given that the compiler might have been configured with a default CPU rather than passing it on the command line. Rather, you should test how the compiler behaves: either run $CC $CFLAGS $CPPFLAGS -E -dM -xc /dev/null and extract and examine predefined macros, or use AC_EGREP_CPP or AC_COMPILE_IFELSE for the same purpose. (If you don't have predefined macros that make all the required ABI distinctions, obviously you need to add them.) There are various examples of this in existing configure / preconfigure fragments. Since there should be a finite list of known ABIs (which would be listed on <https://sourceware.org/glibc/wiki/ABIList> for a port included in glibc), you can then have a finite number of LIBC_SLIBDIR_RTLDDIR calls in a case statement. -- Joseph S. Myers joseph@xxxxxxxxxxxxxxxx _______________________________________________ linux-snps-arc mailing list linux-snps-arc@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/linux-snps-arc
