pkgs/build-support/cc-wrapper/setup-hook.sh

   1 # CC Wrapper hygiene
   2 #
   3 # For at least cross compilation, we need to depend on multiple cc-wrappers at
   4 # once---specifically up to one per sort of dependency. This follows from having
   5 # different tools targeting different platforms, and different flags for those
   6 # tools. For example:
   7 #
   8 #   # Flags for compiling (whether or not linking) C code for the...
   9 #   NIX_CFLAGS_COMPILE_FOR_BUILD  # ...build platform
  10 #   NIX_CFLAGS_COMPILE            # ...host platform
  11 #   NIX_CFLAGS_COMPILE_FOR_TARGET # ...target platform
  12 #
  13 # Notice that these platforms are the 3 *relative* to the package using
  14 # cc-wrapper, not absolute like `x86_64-pc-linux-gnu`.
  15 #
  16 # The simplest solution would be to have separate cc-wrappers per (3 intended
  17 # use-cases * n absolute concrete platforms). For the use-case axis, we would
  18 # @-splice in 'BUILD_' '' 'TARGET_' to use the write environment variables when
  19 # building the cc-wrapper, and likewise prefix the binaries' names so they didn't
  20 # clobber each other on the PATH. But the need for 3x cc-wrappers, along with
  21 # non-standard name prefixes, is annoying and liable to break packages' build
  22 # systems.
  23 #
  24 # Instead, we opt to have just one cc-wrapper per absolute platform. Matching
  25 # convention, the binaries' names can just be prefixed with their target
  26 # platform. On the other hand, that means packages will depend on not just
  27 # multiple cc-wrappers, but the exact same cc-wrapper derivation multiple ways.
  28 # That means the exact same cc-wrapper derivation must be able to avoid
  29 # conflicting with itself, despite the fact that `setup-hook.sh`, the `addCvars`
  30 # function, and `add-flags.sh` are all communicating with each other with
  31 # environment variables. Yuck.
  32 #
  33 # The basic strategy is:
  34 #
  35 #  - Everyone exclusively *adds information* to relative-platform-specific
  36 #    environment variables, like `NIX_CFLAGS_COMPILE_FOR_TARGET`, to communicate
  37 #    with the wrapped binaries.
  38 #
  39 #  - The wrapped binaries will exclusively *read* cc-wrapper-derivation-specific
  40 #    environment variables distinguished with with `suffixSalt`, like
  41 #    `NIX_CFLAGS_COMPILE_@suffixSalt@`.
  42 #
  43 #  - `add-flags`, beyond its old task of reading extra flags stuck inside the
  44 #    cc-wrapper derivation, will convert the relative-platform-specific
  45 #    variables to cc-wrapper-derivation-specific variables. This conversion is
  46 #    the only time all but one of the cc-wrapper-derivation-specific variables
  47 #    are set.
  48 #
  49 # This ensures the flow of information is exclusive from
  50 # relative-platform-specific variables to cc-wrapper-derivation-specific
  51 # variables. This allows us to support the general case of a many--many relation
  52 # between relative platforms and cc-wrapper derivations.
  53 #
  54 # For more details, read the individual files where the mechanisms used to
  55 # accomplish this will be individually documented.
  56
  57 # Skip setup hook if we're neither a build-time dep, nor, temporarily, doing a
  58 # native compile.
  59 #
  60 # TODO(@Ericson2314): No native exception
  61 [[ -z ${strictDeps-} ]] || (( "$hostOffset" < 0 )) || return 0
  62
  63 # It's fine that any other cc-wrapper will redefine this. Bash functions close
  64 # over no state, and there's no @-substitutions within, so any redefined
  65 # function is guaranteed to be exactly the same.
  66 ccWrapper_addCVars () {
  67     # See ../setup-hooks/role.bash
  68     local role_post
  69     getHostRoleEnvHook
  70
  71     if [ -d "$1/include" ]; then
  72         export NIX_CFLAGS_COMPILE${role_post}+=" -isystem $1/include"
  73     fi
  74
  75     if [ -d "$1/Library/Frameworks" ]; then
  76         export NIX_CFLAGS_COMPILE${role_post}+=" -iframework $1/Library/Frameworks"
  77     fi
  78 }
  79
  80 # See ../setup-hooks/role.bash
  81 getTargetRole
  82 getTargetRoleWrapper
  83
  84 # We use the `targetOffset` to choose the right env hook to accumulate the right
  85 # sort of deps (those with that offset).
  86 addEnvHooks "$targetOffset" ccWrapper_addCVars
  87
  88 # Note 1: these come *after* $out in the PATH (see setup.sh).
  89 # Note 2: phase separation makes this look useless to shellcheck.
  90
  91 # shellcheck disable=SC2157
  92 if [ -n "@cc@" ]; then
  93     addToSearchPath _PATH @cc@/bin
  94 fi
  95
  96 # shellcheck disable=SC2157
  97 if [ -n "@libc_bin@" ]; then
  98     addToSearchPath _PATH @libc_bin@/bin
  99 fi
 100
 101 # shellcheck disable=SC2157
 102 if [ -n "@coreutils_bin@" ]; then
 103     addToSearchPath _PATH @coreutils_bin@/bin
 104 fi
 105
 106 # Export tool environment variables so various build systems use the right ones.
 107
 108 export NIX_CC${role_post}=@out@
 109
 110 export CC${role_post}=@named_cc@
 111 export CXX${role_post}=@named_cxx@
 112
 113 # If unset, assume the default hardening flags.
 114 : ${NIX_HARDENING_ENABLE="@default_hardening_flags_str@"}
 115 export NIX_HARDENING_ENABLE
 116
 117 # No local scope in sourced file
 118 unset -v role_post