ircd::ctx::posix: Add linker hooks for specific pthread functions.

ircd/Makefile.am

@@ -20,6 +20,9 @@ AM_LDFLAGS = \
 	-Wl,--no-undefined-version \
 	-Wl,--weak-unresolved-symbols \
 	-Wl,--unresolved-symbols=ignore-in-shared-libs \
+	-Wl,--wrap=pthread_create \
+	-Wl,--wrap=pthread_join \
+	-Wl,--wrap=pthread_self \
 	-Wl,-z,nodelete \
 	-Wl,-z,nodlopen \
 	-Wl,-z,lazy \

ircd/ctx_posix.cc

@@ -15,11 +15,7 @@
 // this time, as we still want real parallel execution ability available to
 // the project and to other users of the address space.
 //
-// This unit is a work in progress. Its eventual goals are non-interference
-// with the rest of the address space, and may even implement the full
-// interface to offer actual functionality of ircd::ctx rather than focused
-// hacks and mitigations.
-//
+
 #include <pthread.h>
 #include <ircd/ctx/posix.h>
 
@@ -39,6 +35,71 @@ ircd::ctx::posix::log
 	"ctx.posix"
 };
 
+//
+// Linker wraps/hooks; see ircd/Makefile.am LDFLAGS. These allow us to play
+// nice with legitimate uses of pthreads by the rest of the address space by
+// appropriately dispatching to either our implementation or the real one.
+//
+
+//
+// hook pthread_create
+//
+
+extern "C" int
+__real_pthread_create(pthread_t *const thread,
+                      const pthread_attr_t *const attr,
+                      void *(*const start_routine)(void *),
+                      void *const arg);
+
+extern "C" int
+__wrap_pthread_create(pthread_t *const thread,
+                      const pthread_attr_t *const attr,
+                      void *(*const start_routine)(void *),
+                      void *const arg)
+{
+	return ircd::ctx::current?
+		ircd_pthread_create(thread, attr, start_routine, arg):
+		__real_pthread_create(thread, attr, start_routine, arg);
+}
+
+//
+// hook pthread_join
+//
+
+extern "C" int
+__real_pthread_join(pthread_t __th,
+                    void **__thread_return);
+
+extern "C" int
+__wrap_pthread_join(pthread_t __th,
+                    void **__thread_return)
+{
+	return ircd::ctx::current?
+		ircd_pthread_join(__th, __thread_return):
+		__real_pthread_join(__th, __thread_return);
+}
+
+//
+// hook pthread_self
+//
+
+extern "C" pthread_t
+__real_pthread_self(void);
+
+extern "C" pthread_t
+__wrap_pthread_self(void)
+{
+	// Note that on the "main" ctx (id=1) we report the real pthread ID
+	return ircd::ctx::current?
+		ircd_pthread_self():
+		__real_pthread_self();
+}
+
+///////////////////////////////////////////////////////////////////////////////
+//
+// pthread supplement
+//
+
 int
 ircd_pthread_create(pthread_t *const thread,
                     const pthread_attr_t *const attr,