changed 7 years ago  
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Toolchain and Build

  • basic build requirements
    • compiler, etc. to bootstrap a new release
    • Guarantee: latest X release can build stable/X+1
    • Willing to guarantee: X-1 and X-2 userland will work on X-CURRENT kernel
  • cross-building from a non-FreeBSD host
  • META_MODE
    • How do we finally turn it on? – src.conf(5)
    • Can you use this without filemon.ko (cross-build)?
      • Would have to check in the dependencies, but wouldn't update them when making changes
  • LLVM sanitizers
    • more architectures (aarch64 and mips64 ASAN in review)
    • amd64 ASAN LLVM tests don't all pass
    • Need a matrix sowing what works
      • asan + threads issue?
    • kernel ubsan? (relatively straightforward)
    • Couple test suite with CI with sanitizers
    • which ones do we want?
      • ASAN
      • UBSAN
      • TSAN
      • profile?
      • xray?
      • msan?
    • Build infrastructure (make goo?) e.g. WITH_ASAN
    • Separate ASAN-built libraries as an option?
  • SSP in GENERIC-DEBUG? WITH_SSP=yes?
  • LLD
    • Current state
      • bootstrap + system linker on amd64, arm64
      • bootstrap linker on i386, armv7
    • Near future (12.0 if possible, else 13)
      • system linker on i386, armv7
      • armv7 flip on and watch for ports fallout
      • MIPS64? (requires -z notext)
  • Userland LTO
    • requires llvm-ar, possibly llvm-nm
    • requires rtld in 11+
    • option for base system? (WITH_LTO)
    • integration/deployment questions
      • -flto produces .o that contain llvm IR (not ELF)
      • llvm-ar emits llvm IR archives
      • new extension for LTO lib vs new libpath vs fat .a
  • Kernel LTO
    • barfed on Dtrace (ctfconvert is unhappy)
      • OpenBSD approach might address this
    • debugging and observability suffers
    • Need to be careful with optimizing out "unnecessary" memory zeroing etc.
    • Link some parts with -flto and not others?
    • -flto=thin vs -flto
  • C11 Atomics vs <machine/atomic.h>
    • marginally better asm
    • ordering with I/O (bus_space_barrier and bus_dmamap_sync)
    • issue with using C11 memory_order_consume to implement RCU in the Linux kernel (papers at http://www.rdrop.com/users/paulmck/RCU/)
  • Enabling compiler support for mitigation features
    • per-arch considerations
    • CFI – needs someone to actually try and test
    • safe stack – ^^^
    • PIE binaries (WITH_PIE)
  • Compressed debug sections / .gdb_index
    • Enable on supported toolchains – needs someone to do and test, probably shouldn't have WITH/WITHOUT, just enable by default
  • Switch llvm back to dwarf4 by default
    • emaste should do this tonight during the hacking lounge
  • clang support for more architectures?
    • RISC-V (can build test application with clang 8, not link)
    • MIPS? (do we care about mips32)
      • mips32 TLS segfaults
      • TLS model is always dynamic
    • powerpc
  • Using newer features (like ifuncs / optimized ifuncs)
    • Ok to start ditching GCC 4.2.x / ld.bfd 2.17.50
    • Requiring vs optionally using features in only one modern toolchain
    • Should we support both toolchains on platforms that support both? Generally yes.
    • Defer question about desupporting modern alternate toolchain.
  • Starting to use C++11 in userland on architectures?
  • Using external toolchain more often (e.g. in regular amd64 development)
    • Manual override to force existing system toolchain
    • Actual testing / documentation of llvm-xtoolchain port
  • LLVM vs elftoolchain
    • ar, nm - for LTO and large .a
      • bug fix needed for elftoolchain, possibly new functionality to be added
    • size, objcopy, readelf, strings - leave as elftc
  • External GCC (base/*)
  • Killing src/contrib/gcc
  • Killing src/contrib/binutils
  • Working with compiler-provided headers (std*.h, etc.)
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