change dynamic TLS installation strategy to optimize access

previously, accesses to dynamic TLS had to check two conditions before
being able to use a dtv slot: (1) that the module index was within the
bounds of the current dtv size, and (2) that the dynamic tls for the
requested module index was already installed in the dtv.

this commit changes the installation strategy so that, whenever an
attempt is made to access dynamic TLS that's not yet installed in the
dtv, the dynamic TLS for all lower-index modules is also installed.
thus it provides a new invariant: if a given module index is within
the bounds of the current dtv size, we automatically know that its TLS
is installed and directly available. the requirement that the second
condition (above) be checked is eliminated.

diff --git a/src/ldso/dynlink.c b/src/ldso/dynlink.c
index 66bca5069bf103f432c689f8e0ae81e0043ea165..2b6f0c94f42049ce39885f783206be3547301ef8 100644 (file)
--- a/src/ldso/dynlink.c
+++ b/src/ldso/dynlink.c
@@ -1034,13 +1034,13 @@ void *__copy_tls(unsigned char *mem)
 void *__tls_get_addr(size_t *v)
 {
        pthread_t self = __pthread_self();
-       if (v[0]<=(size_t)self->dtv[0] && self->dtv[v[0]])
+       if (v[0]<=(size_t)self->dtv[0])
                return (char *)self->dtv[v[0]]+v[1];
 
        /* Block signals to make accessing new TLS async-signal-safe */
        sigset_t set;
        pthread_sigmask(SIG_BLOCK, SIGALL_SET, &set);
-       if (v[0]<=(size_t)self->dtv[0] && self->dtv[v[0]]) {
+       if (v[0]<=(size_t)self->dtv[0]) {
                pthread_sigmask(SIG_SETMASK, &set, 0);
                return (char *)self->dtv[v[0]]+v[1];
        }
@@ -1062,12 +1062,18 @@ void *__tls_get_addr(size_t *v)
                self->dtv = newdtv;
        }
 
-       /* Get new TLS memory from new DSO */
-       unsigned char *mem = p->new_tls +
-               (p->tls_size + p->tls_align) * a_fetch_add(&p->new_tls_idx,1);
-       mem += ((uintptr_t)p->tls_image - (uintptr_t)mem) & (p->tls_align-1);
-       self->dtv[v[0]] = mem;
-       memcpy(mem, p->tls_image, p->tls_len);
+       /* Get new TLS memory from all new DSOs up to the requested one */
+       unsigned char *mem;
+       for (p=head; ; p=p->next) {
+               if (!p->tls_id || self->dtv[p->tls_id]) continue;
+               mem = p->new_tls + (p->tls_size + p->tls_align)
+                       * a_fetch_add(&p->new_tls_idx,1);
+               mem += ((uintptr_t)p->tls_image - (uintptr_t)mem)
+                       & (p->tls_align-1);
+               self->dtv[p->tls_id] = mem;
+               memcpy(mem, p->tls_image, p->tls_len);
+               if (p->tls_id == v[0]) break;
+       }
        pthread_sigmask(SIG_SETMASK, &set, 0);
        return mem + v[1];
 }