From d3d888c943f8f27c83d214b0569e33c4cccf8982 Mon Sep 17 00:00:00 2001
From: Simon McVittie <smcv@collabora.com>
Date: Wed, 18 Sep 2019 13:03:36 +0100
Subject: [PATCH] capture-libs: Treat unversioned libraries as in indeterminate
 order

On at least Debian, Ubuntu and Manjaro, libgcc_s.so.1 is a regular
file, not a symlink to a versioned name (libgcc_s.so.1.2.3) like most
shared libraries.

However, on Fedora 30 it is a symlink to a versioned name like
libgcc_s-9-20190827.so.1. The name used in Fedora happens to be less
than libgcc_s.so.1 in strverscmp() order, causing capsule-capture-libs
to prefer the Debian/Manjaro libgcc_s.so.1, even if the container is
older. This can cause problems if an old Debian-derived container like the
Steam Runtime is used on a newer Fedora host, with host graphics drivers
imported by using capsule-capture-libs: the container's libgcc_s.so.1
does not satisfy the versioned symbol requirements of the graphics driver,
causing loading to fail.

Treat a regular file libgcc_s.so.1 as indeterminate order (or "equal"),
so that we fall back to the default behaviour, which is currently to
take the host version of the library in the case of a tie.

This is a stopgap solution: ideally we would consider the versioned
symbols exported by both libraries, and take whichever one has a superset
of the version definitions exported by the other, if there is a strict
superset in either direction (in the case of libgcc, in fact there is).

Signed-off-by: Simon McVittie <smcv@collabora.com>
---
 utils/capture-libs.c | 41 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/utils/capture-libs.c b/utils/capture-libs.c
index f2e2d28c3..156603403 100644
--- a/utils/capture-libs.c
+++ b/utils/capture-libs.c
@@ -356,6 +356,41 @@ library_cmp_by_name( const char *soname,
          "\"%s\" from \"%s\"",
          soname, left_basename, left_from, right_basename, right_from );
 
+  if( strcmp( left_basename, right_basename ) == 0 )
+  {
+    DEBUG( DEBUG_TOOL,
+           "Name of %s \"%s\" from \"%s\" compares the same as "
+           "\"%s\" from \"%s\"",
+           soname, left_basename, left_from, right_basename, right_from );
+    return 0;
+  }
+
+  if( strcmp( soname, left_basename ) == 0 )
+  {
+    /* In some distributions (Debian, Ubuntu, Manjaro)
+     * libgcc_s.so.1 is a plain file, not a symlink to a
+     * version-suffixed version. We cannot know just from the name
+     * whether that's older or newer, so assume equal. The caller is
+     * responsible for figuring out which one to prefer. */
+    DEBUG( DEBUG_TOOL,
+           "Unversioned %s \"%s\" from \"%s\" cannot be compared with "
+           "\"%s\" from \"%s\"",
+           soname, left_basename, left_from,
+           right_basename, right_from );
+    return 0;
+  }
+
+  if( strcmp( soname, right_basename ) == 0 )
+  {
+    /* The same, but the other way round */
+    DEBUG( DEBUG_TOOL,
+           "%s \"%s\" from \"%s\" cannot be compared with "
+           "unversioned \"%s\" from \"%s\"",
+           soname, left_basename, left_from,
+           right_basename, right_from );
+    return 0;
+  }
+
   return ( strverscmp( left_basename, right_basename ) );
 }
 
@@ -489,6 +524,12 @@ capture_one( const char *soname, capture_flags flags,
             {
                 const char *needed_path_in_container = container.needed[0].path;
 
+                /* TODO: Ideally we would actually dlopen the libraries and
+                 * inspect their symbol tables, either in ambiguous cases
+                 * or always - but that's easier said than done, because
+                 * private symbols exist. For now we just use
+                 * library_cmp_by_name(). */
+
                 /* If equal, we prefer the provider over the container */
                 if( library_cmp_by_name( needed_name,
                                          needed_path_in_container,
-- 
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