Avoid libdl dependencies in bundled libverto

The upstream libverto depends on dynamic loading and in particular on
dladdr(), which is not universal.  To avoid this dependency, stub out
support for module loading (by replacing module.c) and instead
integrate the k5ev module directly into the bundled verto library.

This change removes the need to link, include, and invoke libverto
differently depending on whether we're using the bundled library; we
can always just link with -lverto and call verto_default().

bigredbutton: whitespace
ticket: 7351 (new)

1 files changed, 37 insertions, 3 deletions

diff --git a/src/util/verto/README b/src/util/verto/README
index 8e47610565..6de645f6fb 100644
--- a/src/util/verto/README
+++ b/src/util/verto/README
@@ -1,6 +1,40 @@
-This directory builds a verto library with only a private back-end
-module, for use when the system has no installed verto library.
+This directory builds a verto library with only a private built-in
+module, for use when the system has no installed verto library.  The
+bundled verto cannot dynamically load modules.  From the upstream
+libverto, we take only verto.c and verto-libev.c, and we only build
+the former; the latter is stored here for comparison purposes.  We use
+a stub implementation of module.c to disable dynamic loading support.
 
-The libverto upstream project page is at:
+This private module uses an embedded libev with renamed symbols (so we
+don't leak libev symbols into the namespace on platforms where we
+can't control the export list).  libev has built-in support for this
+kind of embedding, so we don't have to modify the libev sources.
+Following libev's documentation, the following files have been copied
+from the ev sources:
+
+  ev.h
+  ev_vars.h
+  ev_wrap.h
+  ev.c
+  ev_select.c
+  ev_poll.c
+  ev_win32.c
+  Symbols.ev
+
+(Symbols.ev wasn't included in the 4.04 tar file due to an oversight,
+so it is taken from the appropriate tag in libev's source repository.)
+
+To rename the exported symbols, we create rename.h from Symbols.ev.
+We also use Symbols.ev to construct the library export list.
+(Renaming libev's symbols would be unnecessary if libev's embedding
+had support for making its API symbols static, but it currently does
+not.)  The source file verto-k5ev.c wraps ev.c with appropriate
+embedding defines, and then defines the libverto module functions
+using the slightly modified contents of libverto's verto-libev.c.  The
+resulting module table is embedded into verto.c using the
+BUILTIN_MODULE define.
+
+The libverto and libev upstream project pages are at:
 
   https://fedorahosted.org/libverto/
+  http://software.schmorp.de/pkg/libev.html