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authorRich Felker <dalias@aerifal.cx>2012-10-04 16:35:46 -0400
committerRich Felker <dalias@aerifal.cx>2012-10-04 16:35:46 -0400
commit8431d7972fd9be0fdcaff8516316d748e81724bb (patch)
tree53800c9deeaf26a9fedc5f9f574d9694315b510c /src/env/__init_tls.c
parentadefe830dd376be386df5650a09c313c483adf1a (diff)
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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.
Diffstat (limited to 'src/env/__init_tls.c')
-rw-r--r--src/env/__init_tls.c71
1 files changed, 71 insertions, 0 deletions
diff --git a/src/env/__init_tls.c b/src/env/__init_tls.c
new file mode 100644
index 00000000..4a840cf2
--- /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