[ptxdist] [PATCH 1/2] wrapper: add package variable to blacklist compiler flags

[Michael Olbrich <m.olbrich@pengutronix.de>]

Another option to prevent unwanted implicit dependencies.

Signed-off-by: Michael Olbrich <m.olbrich@pengutronix.de>
---
 doc/ref_make_variables.rst             | 8 ++++++++
 rules/post/ptxd_make_world_common.make | 1 +
 scripts/wrapper/libwrapper.sh          | 6 ++++++
 3 files changed, 15 insertions(+)

diff --git a/doc/ref_make_variables.rst b/doc/ref_make_variables.rst
index b770b1b49f18..674acdcea982 100644
--- a/doc/ref_make_variables.rst
+++ b/doc/ref_make_variables.rst
@@ -308,6 +308,14 @@ Build Environment for all Stages
   flags. Adding them via environment variables or ``make`` arguments can
   have unexpected side effects, such as as overwriting existing defaults.
 
+``<PKG>_FLAGS_BLACKLIST``
+  A list of arbitrary flags. If any one of these flags is found as an
+  argument to the compiler, preprocessor or linker then the call will fail.
+  This is useful to prevent implicit dependencies: Many packages try to
+  link to libraries at configure time and use them if it works. Adding
+  '-l<lib>' to the blacklist makes it possible to prevent such a detection
+  and explicitly avoid the dependency.
+
 ``<PKG>_WRAPPER_BLACKLIST``
   PTXdist has several options in the platformconfig that inject options in
   the compiler command line. This is used, for example, to add hardening
diff --git a/rules/post/ptxd_make_world_common.make b/rules/post/ptxd_make_world_common.make
index 172f4c3296af..e5cf50214e9c 100644
--- a/rules/post/ptxd_make_world_common.make
+++ b/rules/post/ptxd_make_world_common.make
@@ -94,6 +94,7 @@ world/env/impl = \
 	pkg_build_dir="$(call ptx/escape,$($(1)_BUILD_DIR))"			\
 										\
 	pkg_wrapper_blacklist="$(call ptx/escape,$($(1)_WRAPPER_BLACKLIST))"	\
+	pkg_flags_blacklist="$(call ptx/escape,$($(1)_FLAGS_BLACKLIST))"	\
 										\
 	pkg_cppflags="$(call ptx/escape,$($(1)_CPPFLAGS))"			\
 	pkg_cflags="$(call ptx/escape,$($(1)_CFLAGS))"				\
diff --git a/scripts/wrapper/libwrapper.sh b/scripts/wrapper/libwrapper.sh
index 0a970638a859..a7cdbeac05dd 100644
--- a/scripts/wrapper/libwrapper.sh
+++ b/scripts/wrapper/libwrapper.sh
@@ -103,6 +103,12 @@ cc_check_args() {
 				COMPILING=true
 				;;
 		esac
+		case " ${pkg_flags_blacklist} " in
+			*" ${ARG} "*)
+				echo "wrapper: found blacklisted flag '${ARG}'" >&2
+				exit 1
+				;;
+		esac
 	done
 	# Used e.g. by the kernel to get the compiler version. Adding
 	# linker options confuses gcc because there is nothing to link.
-- 
2.29.2


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