[json-glib/wip/smcv/default-symver] build: Add a symbol version to all exported symbols

[Simon McVittie <smcv src gnome org>]

commit ef7fb78a5370a5e36272e3bbe91e1864b766a565
Author: Simon McVittie <smcv collabora com>
Date:   Mon Jun 29 17:56:23 2020 +0100

    build: Add a symbol version to all exported symbols
    
    The --default-symver linker option attaches a default version definition
    (the SONAME) to every exported symbol. It is supported since at least
    GNU binutils 2.22 in 2011 (older versions not tested).
    
    With this version definition, newly-linked binaries that depend on the
    json-glib shared library will refer to its symbols in a versioned form,
    preventing their references from being resolved to a symbol of the same
    name exported by json-c or libjansson if those libraries appear in
    dependency search order before json-glib, which will usually result in
    a crash. This is necessary because ELF symbol resolution normally uses
    a single flat namespace, not a tree like Windows symbol resolution.
    At least one symbol (json_object_iter_next()) is exported by all three
    JSON libraries.
    
    Linking with -Bsymbolic is not enough to have this effect in all cases,
    because -Bsymbolic only affects symbol lookup within a shared object,
    for example when json_from_string() calls json_parser_new(). It does
    not affect symbol lookup when external code calls into json-glib,
    for example when libedataserver calls json_parser_new().
    
    This change will also not prevent code that depends on json-c or
    libjansson from finding json-glib's symbols and crashing; to prevent
    that, a corresponding change in json-c or libjansson would be needed.
    
    Adding a symbol-version is a backwards-compatible change, but once
    added, removing or changing the symbol-version would be an incompatible
    change that requires a SONAME bump.
    
    Partially resolves https://gitlab.gnome.org/GNOME/json-glib/-/issues/33
    and https://gitlab.gnome.org/GNOME/glib/-/issues/2147.
    
    Signed-off-by: Simon McVittie <smcv collabora com>

 meson.build | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/meson.build b/meson.build
index f84d865..67d2a5e 100644
--- a/meson.build
+++ b/meson.build
@@ -136,6 +136,7 @@ if host_system == 'linux'
     '-Wl,-Bsymbolic',
     '-Wl,-z,relro',
     '-Wl,-z,now',
+    '-Wl,--default-symver',
   ])
 endif