Add a new function dllockinit() for registering thread locking

functions to be used by the dynamic linker.  This can be called by
threads packages at start-up time.  I will add the call to libc_r
soon.

Also add a default locking method that is used up until dllockinit()
is called.  The default method works by blocking SIGVTALRM, SIGPROF,
and SIGALRM in critical sections.  It is based on the observation
that most user-space threads packages implement thread preemption
with one of these signals (usually SIGVTALRM).

The dynamic linker has never been reentrant, but it became less
reentrant in revision 1.34 of "src/libexec/rtld-elf/rtld.c".
Starting with that revision, multiple threads each doing lazy
binding could interfere with each other.  The usual symptom was
that a symbol was falsely reported as undefined at start-up time.
It was rare but not unseen.  This commit fixes it.

1 files changed, 4 insertions, 0 deletions

diff --git a/libexec/rtld-elf/rtld.h b/libexec/rtld-elf/rtld.h
index c63e7d0..b8fcf2c 100644
--- a/libexec/rtld-elf/rtld.h
+++ b/libexec/rtld-elf/rtld.h
@@ -157,6 +157,10 @@ unsigned long elf_hash(const char *);
 const Elf_Sym *find_symdef(unsigned long, Obj_Entry *, const Obj_Entry **,
   bool);
 void init_pltgot(Obj_Entry *);
+void lockdflt_acquire(void *);
+void *lockdflt_create(void *);
+void lockdflt_destroy(void *);
+void lockdflt_release(void *);
 void obj_free(Obj_Entry *);
 Obj_Entry *obj_new(void);
 int reloc_non_plt(Obj_Entry *, Obj_Entry *);