[cmake][linux][patch][draft] runtime filename/soname miss-detection

[sylware]

The (soname/runtime filename) symbolic link (or copy of the library) may not be in the same directory than the development library. Current macro code will mis-configure the (soname/runtime filename) to the library name.

Be sure we use all the time the (soname/runtime filename) reconstructed from the library filename (Should it be more robust to use the ELF DT_SONAME from the library using binutils objdump?)

--- a/cmake/sdlchecks.cmake
+++ b/cmake/sdlchecks.cmake
@@ -26,9 +26,6 @@ macro(FindLibraryAndSONAME _LIB)
       string(REGEX REPLACE "(\\.[0-9]*)\\.[0-9\\.]*$" "\\1" _LIB_REGEXD "${_LIB_JUSTNAME}")
     endif()
 
-    if(NOT EXISTS "${_LIB_LIBDIR}/${_LIB_REGEXD}")
-      set(_LIB_REGEXD "${_LIB_JUSTNAME}")
-    endif()
     set(${_LNAME}_LIBDIR "${_LIB_LIBDIR}")
 
     message(STATUS "dynamic lib${_LIB} -> ${_LIB_REGEXD}")

[slouken]

@madebr, can you take a look at this?

[madebr]

On Linux, I can extract the soname using:

$ objdump -p /usr/lib64/libX11.so | grep SONAME

How can I do this on other elf/dylib platforms?

[slouken]

How does libtool generate the soname?

[madebr]

How does libtool generate the soname?

Not entirely sure, but a .la file contains this:

# The name that we can dlopen(3).
dlname='libshared.so.0'

# Names of this library.
library_names='libshared.so.0.0.0 libshared.so.0 libshared.so'

# The name of the static archive.
old_library='libshared.a'

[madebr]

I think it makes sense to fall back to the full versioned filename if the SOVERSION'ed library does not exist.
If for some reason SOVERSION library does not exists, then users will still have a functioning SDL library.
It's perhaps not 100% reproducible when you have an incomplete/broken prefix, but SDL should not care about this.

objdump-like parsing would be nice, but hard to reliably implement cross-platform.
Is objdump output standardized? How to do macOS?

[madebr]

I asked on cpplang.slack.com#cmake, and they suggested me to use readelf -d -> objdump -h -> keep path.
Can anyone tell me how to do this with otool for MACHO on macOS?

[sezero]

I asked on cpplang.slack.com#cmake, and they suggested me to use readelf -d -> objdump -h -> keep path. Can anyone tell me how to do this with otool for MACHO on macOS?

If I understand the question correctly, i.e. how to display the install name of a dylib, run otool -L xxxx, you can change it with install_name_tool -id xxxxx

[madebr]

If I understand the question correctly, i.e. how to display the install name of a dylib, run otool -L xxxx, you can change it with install_name_tool -id xxxxx

I want to know how to go from libX11.dylib to libX11.dylib.4.
Something like this, but for Apple:

readelf -d /usr/lib64/libX11.so  | grep SONAME | sed -r 's/.*\[([^\]+)].*/\1/'

[smcv]

I think it makes sense to fall back to the full versioned filename if the SOVERSION'ed library does not exist.

Do you mean for example if discovering the SONAME of libwayland-client.so.0 failed, you'd want to hard-code libwayland-client.so.0.23.1 into the library?

I think that would be a bad idea: when distributions apply even a micro-version update to a library, the full versioned filename is expected to change, and that would silently break a previously-compiled SDL if it hard-coded the full versioned filename. On platforms like desktop Linux and FreeBSD (but notably not Android or OpenBSD) that use versioned SONAMEs, the SONAME is the only name we should be attempting to load at runtime: see e.g. #15172 for reasoning.

[smcv]

In case it helps, here is an implementation of parsing ELF binaries using libelf (a minimalistic machine-readable readelf-equivalent, if you want to look at it that way): https://salsa.debian.org/gnome-team/gobject-introspection/-/blob/debian/1.86.0-6/debian/elf-get-needed.c?ref_type=tags

To output the SONAME the only change would be dyn->d_tag == DT_SONAME instead of dyn->d_tag == DT_NEEDED.