TLS (GNU/C11 thread-local storage) support for static-linked programs

the design for TLS in dynamic-linked programs is mostly complete too,
but I have not yet implemented it. cost is nonzero but still low for
programs which do not use TLS and/or do not use threads (a few hundred
bytes of new code, plus dependency on memcpy). i believe it can be
made smaller at some point by merging __init_tls and __init_security
into __libc_start_main and avoiding duplicate auxv-parsing code.

at the same time, I've also slightly changed the logic pthread_create
uses to allocate guard pages to ensure that guard pages are not
counted towards commit charge.

diff --git a/src/env/__init_tls.c b/src/env/__init_tls.c
new file mode 100644 (file)
index 0000000..4a840cf
--- /dev/null
+++ b/src/env/__init_tls.c
@@ -0,0 +1,71 @@
+#include <elf.h>
+#include <limits.h>
+#include "pthread_impl.h"
+#include "libc.h"
+#include "atomic.h"
+
+#ifndef SHARED
+
+static void *image;
+static size_t len, bss, align;
+
+void *__copy_tls(unsigned char *mem, size_t cnt)
+{
+       mem += ((uintptr_t)image - (uintptr_t)mem) & (align-1);
+       memcpy(mem, image, len);
+       return mem + len + bss;
+}
+
+static void *simple(void *p)
+{
+       *(void **)p = p;
+       return __set_thread_area(p) ? 0 : p;
+}
+
+weak_alias(simple, __install_initial_tls);
+
+void *__mmap(void *, size_t, int, int, int, off_t);
+
+#if ULONG_MAX == 0xffffffff
+typedef Elf32_Phdr Phdr;
+#else
+typedef Elf64_Phdr Phdr;
+#endif
+
+#define AUX_CNT 6
+
+void __init_tls(size_t *auxv)
+{
+       size_t i, aux[AUX_CNT] = { 0 };
+       unsigned char *p, *mem;
+       size_t n, d;
+       Phdr *phdr, *tls_phdr=0;
+       size_t base = 0;
+
+       for (; auxv[0]; auxv+=2) if (auxv[0]<AUX_CNT) aux[auxv[0]] = auxv[1];
+       p = (void *)aux[AT_PHDR];
+       for (p=(void *)aux[AT_PHDR]; aux[AT_PHNUM]--; p+=aux[AT_PHENT]) {
+               phdr = (void *)p;
+               if (phdr->p_type == PT_PHDR)
+                       base = aux[AT_PHDR] - phdr->p_vaddr;
+               if (phdr->p_type == PT_TLS)
+                       tls_phdr = phdr;
+       }
+       if (!tls_phdr) return;
+
+       libc.tls_size = len+bss+align+4*sizeof(size_t)+sizeof(struct pthread);
+
+       image = (void *)(base + tls_phdr->p_vaddr);
+       len = tls_phdr->p_filesz;
+       bss = tls_phdr->p_memsz - len;
+       align = tls_phdr->p_align;
+       if (align < 4*sizeof(size_t)) align = 4*sizeof(size_t);
+       mem = __mmap(0, libc.tls_size, PROT_READ|PROT_WRITE,
+               MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);
+       if (mem == MAP_FAILED) a_crash();
+
+       if (!__install_initial_tls(__copy_tls(mem, 0))) a_crash();
+}
+#else
+void __init_tls(size_t *auxv) { }
+#endif

diff --git a/src/env/__libc_start_main.c b/src/env/__libc_start_main.c
index f31222b..a38569d 100644 (file)
--- a/src/env/__libc_start_main.c
+++ b/src/env/__libc_start_main.c
@@ -1,5 +1,6 @@
 #include "libc.h"
 
+void __init_tls(size_t *);
 void __init_security(size_t *);
 
 int __libc_start_main(
@@ -15,6 +16,7 @@ int __libc_start_main(
        libc.ldso_fini = ldso_fini;
        libc.fini = fini;
 
+       __init_tls((void *)auxv);
        __init_security((void *)auxv);
 
        /* Execute constructors (static) linked into the application */

diff --git a/src/internal/libc.h b/src/internal/libc.h
index ea863d6..ca06f31 100644 (file)
--- a/src/internal/libc.h
+++ b/src/internal/libc.h
@@ -16,6 +16,7 @@ struct __libc {
        int canceldisable;
        FILE *ofl_head;
        int ofl_lock[2];
+       volatile size_t tls_size, tls_cnt;
 };
 
 extern size_t __hwcap;

diff --git a/src/ldso/dynlink.c b/src/ldso/dynlink.c
index 960e089..1447e20 100644 (file)
--- a/src/ldso/dynlink.c
+++ b/src/ldso/dynlink.c
@@ -17,6 +17,9 @@
 #include <pthread.h>
 #include <ctype.h>
 #include <dlfcn.h>
+#include "pthread_impl.h"
+#include "libc.h"
+#undef libc
 
 static int errflag;
 static char errbuf[128];
@@ -788,6 +791,8 @@ void *__dynlink(int argc, char **argv)
        debug.state = 0;
        _dl_debug_state();
 
+       /* Stand-in until real TLS support is added to dynamic linker */
+       __libc.tls_size = sizeof(struct pthread) + 4*sizeof(size_t);
        if (ssp_used) __init_ssp(auxv);
 
        do_init_fini(tail);
@@ -802,6 +807,11 @@ void *__dynlink(int argc, char **argv)
        return (void *)aux[AT_ENTRY];
 }
 
+void *__copy_tls(unsigned char *mem, size_t cnt)
+{
+       return mem;
+}
+
 void *dlopen(const char *file, int mode)
 {
        struct dso *volatile p, *orig_tail = tail, *next;

diff --git a/src/thread/pthread_create.c b/src/thread/pthread_create.c
index d8b8f0f..f53fc1b 100644 (file)
--- a/src/thread/pthread_create.c
+++ b/src/thread/pthread_create.c
@@ -84,6 +84,8 @@ static void init_file_lock(FILE *f)
        if (f && f->lock<0) f->lock = 0;
 }
 
+void *__copy_tls(unsigned char *, size_t);
+
 int pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict attr, void *(*entry)(void *), void *restrict arg)
 {
        int ret;
@@ -92,6 +94,8 @@ int pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict attr,
        struct pthread *self = pthread_self(), *new;
        unsigned char *map, *stack, *tsd;
        unsigned flags = 0x7d8f00;
+       size_t tls_cnt = libc.tls_cnt;
+       size_t tls_size = libc.tls_size;
 
        if (!self) return ENOSYS;
        if (!libc.threaded) {
@@ -109,15 +113,24 @@ int pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict attr,
        } else {
                if (attr) {
                        guard = ROUND(attr->_a_guardsize + DEFAULT_GUARD_SIZE);
-                       size = guard + ROUND(attr->_a_stacksize + DEFAULT_STACK_SIZE);
+                       size = guard + ROUND(attr->_a_stacksize
+                               + DEFAULT_STACK_SIZE + tls_size);
                }
                size += __pthread_tsd_size;
-               map = mmap(0, size, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANON, -1, 0);
-               if (map == MAP_FAILED) return EAGAIN;
-               if (guard) mprotect(map, guard, PROT_NONE);
+               if (guard) {
+                       map = mmap(0, size, PROT_NONE, MAP_PRIVATE|MAP_ANON, -1, 0);
+                       if (map == MAP_FAILED) return EAGAIN;
+                       if (mprotect(map+guard, size-guard, PROT_READ|PROT_WRITE)) {
+                               munmap(map, size);
+                               return EAGAIN;
+                       }
+               } else {
+                       map = mmap(0, size, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANON, -1, 0);
+                       if (map == MAP_FAILED) return EAGAIN;
+               }
                tsd = map + size - __pthread_tsd_size;
        }
-       new = (void *)(tsd - sizeof *new - PAGE_SIZE%sizeof *new);
+       new = __copy_tls(tsd - tls_size, tls_cnt);
        new->map_base = map;
        new->map_size = size;
        new->pid = self->pid;

diff --git a/src/thread/pthread_self.c b/src/thread/pthread_self.c
index a8cc80b..a93d812 100644 (file)
--- a/src/thread/pthread_self.c
+++ b/src/thread/pthread_self.c
@@ -1,6 +1,6 @@
 #include "pthread_impl.h"
 
-static struct pthread main_thread;
+static struct pthread *main_thread = &(struct pthread){0};
 
 /* pthread_key_create.c overrides this */
 static const void *dummy[1] = { 0 };
@@ -10,14 +10,14 @@ static int init_main_thread()
 {
        __syscall(SYS_rt_sigprocmask, SIG_UNBLOCK,
                SIGPT_SET, 0, __SYSCALL_SSLEN);
-       if (__set_thread_area(&main_thread) < 0) return -1;
-       main_thread.canceldisable = libc.canceldisable;
-       main_thread.tsd = (void **)__pthread_tsd_main;
-       main_thread.errno_ptr = __errno_location();
-       main_thread.self = &main_thread;
-       main_thread.tid = main_thread.pid =
-               __syscall(SYS_set_tid_address, &main_thread.tid);
-       libc.main_thread = &main_thread;
+       if (__set_thread_area(main_thread) < 0) return -1;
+       main_thread->canceldisable = libc.canceldisable;
+       main_thread->tsd = (void **)__pthread_tsd_main;
+       main_thread->errno_ptr = __errno_location();
+       main_thread->self = main_thread;
+       main_thread->tid = main_thread->pid =
+               __syscall(SYS_set_tid_address, &main_thread->tid);
+       libc.main_thread = main_thread;
        return 0;
 }
 
@@ -35,3 +35,9 @@ pthread_t __pthread_self_def()
 
 weak_alias(__pthread_self_def, pthread_self);
 weak_alias(__pthread_self_def, __pthread_self_init);
+
+void *__install_initial_tls(void *p)
+{
+       main_thread = p;
+       return __pthread_self_def();
+}