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120 lines
4.6 KiB
120 lines
4.6 KiB
# CC Wrapper hygiene
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#
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# For at least cross compilation, we need to depend on multiple cc-wrappers at
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# once---specifically up to one per sort of dependency. This follows from having
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# different tools targeting different platforms, and different flags for those
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# tools. For example:
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#
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# # Flags for compiling (whether or not linking) C code for the...
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# NIX_CFLAGS_COMPILE_FOR_BUILD # ...build platform
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# NIX_CFLAGS_COMPILE # ...host platform
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# NIX_CFLAGS_COMPILE_FOR_TARGET # ...target platform
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#
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# Notice that these platforms are the 3 *relative* to the package using
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# cc-wrapper, not absolute like `x86_64-pc-linux-gnu`.
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#
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# The simplest solution would be to have separate cc-wrappers per (3 intended
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# use-cases * n absolute concrete platforms). For the use-case axis, we would
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# @-splice in 'BUILD_' '' 'TARGET_' to use the write environment variables when
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# building the cc-wrapper, and likewise prefix the binaries' names so they didn't
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# clobber each other on the PATH. But the need for 3x cc-wrappers, along with
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# non-standard name prefixes, is annoying and liable to break packages' build
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# systems.
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#
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# Instead, we opt to have just one cc-wrapper per absolute platform. Matching
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# convention, the binaries' names can just be prefixed with their target
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# platform. On the other hand, that means packages will depend on not just
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# multiple cc-wrappers, but the exact same cc-wrapper derivation multiple ways.
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# That means the exact same cc-wrapper derivation must be able to avoid
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# conflicting with itself, despite the fact that `setup-hook.sh`, the `addCvars`
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# function, and `add-flags.sh` are all communicating with each other with
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# environment variables. Yuck.
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#
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# The basic strategy is:
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#
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# - Everyone exclusively *adds information* to relative-platform-specific
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# environment variables, like `NIX_CFLAGS_COMPILE_FOR_TARGET`, to communicate
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# with the wrapped binaries.
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#
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# - The wrapped binaries will exclusively *read* cc-wrapper-derivation-specific
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# environment variables distinguished with with `suffixSalt`, like
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# `NIX_CFLAGS_COMPILE_@suffixSalt@`.
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#
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# - `add-flags`, beyond its old task of reading extra flags stuck inside the
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# cc-wrapper derivation, will convert the relative-platform-specific
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# variables to cc-wrapper-derivation-specific variables. This conversion is
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# the only time all but one of the cc-wrapper-derivation-specific variables
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# are set.
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#
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# This ensures the flow of information is exclusive from
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# relative-platform-specific variables to cc-wrapper-derivation-specific
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# variables. This allows us to support the general case of a many--many relation
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# between relative platforms and cc-wrapper derivations.
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#
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# For more details, read the individual files where the mechanisms used to
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# accomplish this will be individually documented.
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# Skip setup hook if we're neither a build-time dep, nor, temporarily, doing a
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# native compile.
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#
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# TODO(@Ericson2314): No native exception
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[[ -z ${strictDeps-} ]] || (( "$hostOffset" < 0 )) || return 0
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# It's fine that any other cc-wrapper will redefine this. Bash functions close
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# over no state, and there's no @-substitutions within, so any redefined
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# function is guaranteed to be exactly the same.
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ccWrapper_addCVars () {
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# See ../setup-hooks/role.bash
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local role_post
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getHostRoleEnvHook
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if [ -d "$1/include" ]; then
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export NIX_CFLAGS_COMPILE${role_post}+=" -isystem $1/include"
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fi
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if [ -d "$1/Library/Frameworks" ]; then
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export NIX_CFLAGS_COMPILE${role_post}+=" -iframework $1/Library/Frameworks"
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fi
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}
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# See ../setup-hooks/role.bash
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getTargetRole
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getTargetRoleWrapper
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# We use the `targetOffset` to choose the right env hook to accumulate the right
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# sort of deps (those with that offset).
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addEnvHooks "$targetOffset" ccWrapper_addCVars
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# Note 1: these come *after* $out in the PATH (see setup.sh).
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# Note 2: phase separation makes this look useless to shellcheck.
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# shellcheck disable=SC2157
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if [ -n "@cc@" ]; then
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addToSearchPath _PATH @cc@/bin
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fi
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# shellcheck disable=SC2157
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if [ -n "@libc_bin@" ]; then
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addToSearchPath _PATH @libc_bin@/bin
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fi
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# shellcheck disable=SC2157
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if [ -n "@coreutils_bin@" ]; then
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addToSearchPath _PATH @coreutils_bin@/bin
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fi
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# Export tool environment variables so various build systems use the right ones.
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export NIX_CC${role_post}=@out@
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export CC${role_post}=@named_cc@
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export CXX${role_post}=@named_cxx@
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export CC${role_post}=@named_cc@
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export CXX${role_post}=@named_cxx@
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# If unset, assume the default hardening flags.
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: ${NIX_HARDENING_ENABLE="fortify stackprotector pic strictoverflow format relro bindnow"}
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export NIX_HARDENING_ENABLE
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# No local scope in sourced file
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unset -v role_post
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