before this change, we included `-ffile-prefix-map=${CMAKE_SOURCE_DIR}=.`
in cflags when building the tree with CMake, but this was wrong.
as the "." directory is the build directory used by CMake. and this
directory is specified by the `-B` option when generating the building
system. if `configure.py --use-cmake` is used to build the tree,
the build directory would be "build". so this option instructs the compiler
to replace the directory of source file in the debug symbols and in
`__FILE__` at compile time.
but, in a typical workspace, for instance, `build/main.cc` does not exist.
the reason why this does not apply to CMake but applies to the rules
generated by `configure.py` is that, `configure.py` puts the generated
`build.ninja` right under the top source directory, so `.` is correct and
it helps to create reproducible builds. because this practically erases
the path prefixes in the build output. while CMake puts it under the
specified build directory, replacing the source directory with the build
directory with the file prefix map is just wrong.
there are two options to address this problem:
* stop passing this option. but this would lead to non-reproducible
builds. as we would encode the build directory in the "scylla"
executable. if a developer needs to rebuild an executable for debugging
a coredump generated in production, he/she would have to either
build the tree in the same directory as our CI does. or, he/she
has to pass `-ffile-prefix-map=...` to map the local build directory
to the one used by CI. this is not convenient.
* instead of using `${CMAKE_SOURCE_DIR}=.`, add `${CMAKE_BINARY_DIR}=.`.
this erases the build directory in the outputs, but preserves the
debuggability.
so we pick the second solution.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#20329
dbb056f4f7