fix(cmakev2/component): fix component library link with whole archive

The current approach involves wrapping the library target within the
library interface target with the whole-archive flags, such as for the
GCC linker. However, this does not work as expected because the library
target is expanded, and the whole-archive flags are also applied to
other library targets that the wrapped library target depends on. IOW
the whole-archive flags surround multiple archives, not just the one
requrested.  Generally, using linker flags like whole-archive in the
library INTERFACE(INTERFACE_LINK_LIBRARIES) does not seem to work as
CMake may perform deduplication and rearrange the flags [1].

The proof of concept used `CMAKE_LINK_LIBRARY_USING_<FEATURE>` with the
WHOLE_ARCHIVE feature, which was introduced in CMake 3.24 to specify how
the library target should be linked. There are two issues with this.
First, this feature is only available from CMake 3.24 onwards, while our
minimum CMake version is set to 3.22. More importantly, all occurrences
of a library on the link line are wrapped.  For example, if a library
like `vfs` appears multiple times on the link line due to dependencies,
each occurrence will be wrapped with whole-archive, causing the linker
to complain about multiple symbol definitions. Therefore, even though
WHOLE_ARCHIVE is recommended for handling whole-archive linkage, it does
not seem suitable for our purposes. This was overlooked in the PoC
because only a simple testing component was used to check the
WHOLE_ARCHIVE behavior.

One way to address this issue is to adopt the same approach used in
cmakev1, which involves specifying the whole-archive flags when linking
component library targets to the final executable. In this case, CMake
retains the flags without any alteration, unlike when the flags are
specified in INTERFACE_LINK_LIBRARIES for the component interface
targets. While this approach is feasible, it would alter the current
logic, where we have a single library interface for the entire idf
library that can be linked to the executable. This change would also
complicate the direct use of the idf library, as it would no longer be
possible to simply link it to the executable. Instead, the executable
would need to correctly link the component libraries with the
whole-archive flags. We could encapsulate this process within the
idf_build_executable function, but projects that only use
idf_build_library would need to implement the same solution.

It appears possible to address this issue by using target_link_options
instead. This allows to specify exactly what should appear on the link
command line. One side effect of this approach is that the library
appears on the link command line multiple times: first when used with
target_link_options and second when used in target_link_libraries.
However, this does not seem to pose a problem. The flags specified with
target_link_options appear on the command line first, ensuring that the
whole-archive is prioritized, and the component archive libraries may be
repeated on the link line anyway due to dependencies. Essentially, the
final link command line is very similar to the one from cmakev1. We may
revisit this approach in the future, but for now, it seems to work as
expected.

[1] https://gitlab.kitware.com/cmake/cmake/-/issues/20078
[2] https://cmake.org/cmake/help/latest/variable/CMAKE_LINK_LIBRARY_USING_FEATURE.html
[3] https://discourse.cmake.org/t/automatically-wrapping-a-static-library-
    in-whole-archive-no-whole-archive-when-used-during-linking/5883

Signed-off-by: Frantisek Hrbata <frantisek.hrbata@espressif.com>
This commit is contained in:
Frantisek Hrbata
2025-11-04 07:48:15 +01:00
parent c2e54b259c
commit 72e96e4907
+6 -4
View File
@@ -913,11 +913,13 @@ function(idf_component_include name)
if(whole_archive)
idf_build_get_property(linker_type LINKER_TYPE)
if(linker_type STREQUAL "GNU")
target_link_libraries("${component_interface}" INTERFACE
"-Wl,--whole-archive" "${component_real_target}" "-Wl,--no-whole-archive")
target_link_options("${component_interface}" INTERFACE
"SHELL:-Wl,--whole-archive $<TARGET_FILE:${component_real_target}> -Wl,--no-whole-archive")
target_link_libraries("${component_interface}" INTERFACE "${component_real_target}")
elseif(linker_type STREQUAL "Darwin")
target_link_libraries("${component_interface}" INTERFACE
"-Wl,-force_load" "${component_real_target}")
target_link_options("${component_interface}" INTERFACE
"SHELL:-Wl,-force_load $<TARGET_FILE:${component_real_target}>")
target_link_libraries("${component_interface}" INTERFACE "${component_real_target}")
endif()
else()
target_link_libraries("${component_interface}" INTERFACE "${component_real_target}")