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Classify explicit toolchain features into shared and platform-specific groups #84
Description
What
Review the current explicit C++ toolchain feature model and classify each feature into one of the following groups:
- shared/common across Linux and QNX
- Linux-specific
- QNX-specific
- consumer-extensible via
extra_known_features/extra_enabled_features
This task establishes the architectural boundary needed for the refactoring Epic.
Acceptance Criteria (DoD)
- A documented classification exists for all explicitly modeled toolchain features.
- Each feature is assigned to exactly one primary ownership group.
- The classification identifies which features are safe to share and which must remain platform-specific.
- The result is detailed enough to guide follow-up extraction and refactoring tasks.
How
- Review the current Linux and QNX toolchain templates.
- Enumerate explicitly defined features and note their purpose, enabled state, and action coverage.
- Compare Linux and QNX feature behavior to identify true overlap versus superficial similarity.
- Record the final classification in a maintainer-facing design note or tracking document.
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cc_featurecomposition #83armando-martins commentedon Jul 22, 2026
Classification groups
Each feature belongs to exactly one primary ownership group:
extra_known_features/extra_enabled_features; not intrinsic to either template.Capability markers
no_legacy_featuressupports_picsupports_dynamic_linkerdbgdbgflag sets in other features.optoptflag sets in other features.supports_fissionsupports_header_path_normalizationCompilation — core flag features
unfiltered_compile_flags__DATE__/__TIME__/__TIMESTAMP__and-Wno-builtin-macro-redefined. Applied to C and C++ compile actions.random_seed-frandom-seed=%{output_file}on c_compile, cpp_compile, cpp_module_compile, cpp_module_codegen.include_paths-iquote,-I,-isystemfrom the corresponding build variables across all compile actions.preprocessor_defines-D%{preprocessor_defines}across all compile actions.user_compile_flagsuser_compile_flagsbuild variable through all compile actions.compiler_input_flags-c %{source_file}across all compile actions.compiler_output_flags-S/-E/-o %{output_file}across all compile actions.pic-fPICguarded byexpand_if_available = "pic"across assemble, preprocess_assemble, c_compile, cpp_compile, cpp_module_codegen, cpp_module_compile.default_compile_flags-m64/ ARM64) flags, agnu11-conditional C standard switch (-std=c11vs-std=gnu11), and a broad set of hardening flags (-fstack-protector,-fno-omit-frame-pointer, etc.). QNX applies-V%{tc_version},gcc_nto%{tc_cpu}for QCC version routing,-std=c11unconditionally viaDEFAULT_C_COMPILE_FLAGS, and a much shorter default flag list.dbg/optactivation logic is structurally identical across both.compiler_library_search_paths%{compiler_library_search_paths_switch}LD_LIBRARY_PATHso that the GCC binary finds its own shared-library dependencies at compile time. Not needed for QNX's QCC, which manages its own library paths internally.gnu11-std=c11(the default) to-std=gnu11insidedefault_compile_flags. QNX uses a fixed-std=c11viaDEFAULT_C_COMPILE_FLAGSwith no equivalent toggle.includes-include %{includes}for force-included headers. Present in the legacy-feature set that Linux restores explicitly; not defined in the QNX template.per_object_debug_info-gsplit-dwarf -gonly whenper_object_debug_info_fileis available (i.e., under--fission). No-op for normal builds.dependency_file-MD -MF %{dependency_file}. QNX wraps the flags for QCC:-Wc,-MD,%{dependency_file}/-Wp,-MD,%{dependency_file}, and the feature is additionally gated by thedependency_file_named_implicitlytoggle. Sharing requires either parameterisation or platform-specific implementations.dependency_file_named_implicitlydependency_filebetween explicit-name and implicit-name modes — a QCC-specific behaviour with no Linux counterpart.Linking and archiving
archiver_flagsrcsD %{output_execpath}plus object-file iteration anduser_archiver_flagspassthrough forcpp_link_static_library.user_link_flagsuser_link_flagsbuild variable through all link actions.linker_param_file@%{linker_param_file}across all link and static-archive actions.library_search_directories-L%{library_search_directories}across all link actions.shared_flag-sharedforcpp_link_dynamic_libraryandcpp_link_nodeps_dynamic_library.output_execpath_flags-o %{output_execpath}across all link actions.libraries_to_linklibraries_to_linkbuild variable.runtime_library_search_directoriesis_cc_test:$ORIGIN/…for tests,$EXEC_ORIGIN/…for non-tests. QNX always uses$EXEC_ORIGIN/…(no test fork) and uses-Wl,-rpathwrapping as required by QCC.default_link_flagsextra_link_flagsis active)-lm -ldl -lrt -static-libstdc++ -static-libgcc, adds-Wl,--gc-sectionsunderopt, and adds-Wl,--compress-debug-sections=zlibin non-opt builds. QNX prepends-V%{tc_version},gcc_nto%{tc_cpu}_cxxfor QCC version routing and links-Wl,-z,relro -Wl,-z,now -lc++ -lm. Additionally, on Linuxdefault_link_flagsis mutually exclusive withextra_link_flags(one disables the other), whereas on QNXextra_link_flagsimpliesdefault_link_flags(both are additive).sysroot_link_flags--sysroot=/-Wl,--sysroot=at link. QNX uses an SDP host/target directory scheme (sdp_env) rather than a sysroot.use_pthread-pthread. QNX's threading is bundled intolibcand requires no separate linker flag.fission_support-Wl,--gdb-indexonly whenis_using_fissionis available (i.e., under--fission). No-op for normal builds.linkstamps%{linkstamp_paths}objects to the linker; only populated under--stamp. No-op otherwise.force_pic_flags-pieforcpp_link_executableonly whenforce_picis available (i.e., under--force_pic). No-op otherwise.strip_debug_symbols-Wl,-Sonly whenstrip_debug_symbolsis available (build mode active). No-op otherwise.static_libgcc-static-libgcconly when thestatic_link_cpp_runtimesfeature is also active. No-op otherwise.fully_static_link-staticunconditionally for all link actions when enabled — intentionally disabled by default because it forces fully static linking for every target. Users must enable explicitly.Warnings
minimal_warnings-Wall,-Wcast-align,-Wformat=2, dozens more). QNX ships a minimal set (-Wall,-Wno-error=deprecated-declarations, one GCC-12.2-specific suppression) and enables it by default. Not safe to share without parameterisation.strict_warningsimplies = ["minimal_warnings"]andenabled = False. Linux adds a significant set of strict flags (-Wconversion,-Wpedantic,-Wextra, etc.). QNX adds only-Wextra -Wpedantic. Structure is shareable; flag content is platform-specific.all_wall_warningsimplies = ["strict_warnings"]andenabled = False. Linux defines a comprehensive set of ~60 flags. QNX defines an empty set (all threeALL_WALL_*groups are[]). Structurally shareable but semantically Linux-only content; sharing would require platform-specific flag injection.warnings_as_errors-Werror -Wno-error=deprecated-declarations. QNX emits only-Werror. Structurally identical; flag lists are platform-specific.Coverage
coveragegcc_coverage_map_format.gcc_coverage_map_format-fprofile-arcs -ftest-coverageguarded bygcov_gcno_file). Link-side: Linux emits--coverage; QNX emits-lgcov. Bothrequires = [feature_set(features = ["coverage"])]. Extractable only with a platform-specific link flag parameter.Extra flag hooks
extra_compile_flags%{extra_compile_flags_switch}implies = ["default_compile_flags"]; QNX also hasimplies = ["default_compile_flags"]. Structurally similar; Linux additionally provides the split variants below.extra_c_compile_flags%{extra_c_compile_flags_switch}extra_compile_flagscovers all compile actions.extra_cxx_compile_flags%{extra_cxx_compile_flags_switch}extra_link_flags%{extra_link_flags_switch}extra_link_flagsdisablesdefault_link_flags(only one active at a time). QNX:extra_link_flagsimpliesdefault_link_flags(additive).QNX environment
sdp_envQNX_HOST,QNX_TARGET,QNX_CONFIGURATION_EXCLUSIVE, andQNX_SHARED_LICENSE_FILEenvironment variables into all compile and link actions. No Linux counterpart; Linux tools find their dependencies viarpathandLD_LIBRARY_PATH.qnx_license_env_info%{use_license_info}Consumer-extensible
extra_known_featuresattributecc_featurelabels passed to the rule. Each is added to the feature list in a disabled state. Consumers can activate them per target viafeatures = [...]or globally via--features. Identical mechanism on both platforms.extra_enabled_featuresattributecc_featurelabels passed to the rule. Each is added to the feature list in an enabled state. Identical mechanism on both platforms.nradakovic commentedon Aug 13, 2026
Done as part of this ticket thread.