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  1. Sep 08, 2022
    • Simon McVittie's avatar
      Build a shim libcurl that can dispatch to runtime or system copies · 74499151
      Simon McVittie authored
      
      This works around ABI divergence from upstream in the libcurl in
      Debian/Ubuntu between about 2005 and 2018, which unfortunately includes
      the time at which Steam Runtime 1 'scout' started. Modern versions of
      libcurl have versioned symbols attached to a verdef CURL_OPENSSL_4,
      but Debian introduced versioned symbols before upstream did, and used
      CURL_OPENSSL_3. We want to be compatible with both.
      
      Similarly, modern upstream versions of libcurl when built against GNUTLS
      have versioned symbols attached to a verdef CURL_GNUTLS_4, but Debian
      introduced versioned symbols attached to a verdef CURL_GNUTLS_3, and
      is still using that verdef as of 2022. We want to be compatible with
      both, if we can.
      
      The trick here is that since glibc 2.30, the dynamic linker does not
      require triples (SONAME, version, symbol), but only looks for pairs of
      (SONAME, version) and, independently, (version, symbol). This means that
      dependencies on versioned symbols can be satisfied by any of the
      recursive dependencies of the library found when searching for the
      SONAME, and not just the library itself. glibc seems to have introduced
      this functionality so that glibc itself would be able to move symbols
      from its smaller libraries into libc.so.6 without breaking compatibility.
      
      The shim library has verdefs for both sets of versioned symbols, so it
      can be positioned in the search path as libcurl.so.4 and will satisfy
      both sets of requirements for the verdefs. For the actual symbols, it
      delegates to libsteam-runtime-system-libcurl.so.4 and
      libsteam-runtime-our-libcurl.so.4, which are expected to be set up by
      the runtime's setup.sh as symlinks to the real libraries that implement
      the two faces of libcurl.
      
      This requires some setup, which will be coordinated by a new version of
      setup.sh, in each of the pinned_libs_* directories. The real work is done
      by libcurl-compat/compat-setup.c, which uses the steam-runtime-tools
      library to find out whether the system libcurl is compatible with the
      expected ABIs.
      
      If there is no system copy of libcurl, then we do not need to do all
      this and can use the runtime's libcurl directly: binaries that rely on
      having a newer libcurl will fail, but by definition those binaries
      can't have been built or tested against the scout runtime.
      
      Helps: steamrt/tasks#119
      Signed-off-by: default avatarSimon McVittie <smcv@collabora.com>
      74499151
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