3 files changed, 108 insertions, 5 deletions

diff --git a/arch/x86_64/syscall_arch.h b/arch/x86_64/syscall_arch.h
index a85c440c..a7a7b5a6 100644
--- a/arch/x86_64/syscall_arch.h
+++ b/arch/x86_64/syscall_arch.h
@@ -60,3 +60,7 @@ static __inline long __syscall6(long n, long a1, long a2, long a3, long a4, long
 						  "d"(a3), "r"(r10), "r"(r8), "r"(r9) : "rcx", "r11", "memory");
 	return ret;
 }
+
+#define VDSO_USEFUL
+#define VDSO_CGT_SYM "__vdso_clock_gettime"
+#define VDSO_CGT_VER "LINUX_2.6"
diff --git a/src/internal/vdso.c b/src/internal/vdso.c
new file mode 100644
index 00000000..6ae0212e
--- /dev/null
+++ b/src/internal/vdso.c
@@ -0,0 +1,91 @@
+#include <elf.h>
+#include <limits.h>
+#include <stdint.h>
+#include <string.h>
+#include "libc.h"
+#include "syscall.h"
+
+#ifdef VDSO_USEFUL
+
+#if ULONG_MAX == 0xffffffff
+typedef Elf32_Ehdr Ehdr;
+typedef Elf32_Phdr Phdr;
+typedef Elf32_Sym Sym;
+typedef Elf32_Verdef Verdef;
+typedef Elf32_Verdaux Verdaux;
+#else
+typedef Elf64_Ehdr Ehdr;
+typedef Elf64_Phdr Phdr;
+typedef Elf64_Sym Sym;
+typedef Elf64_Verdef Verdef;
+typedef Elf64_Verdaux Verdaux;
+#endif
+
+static int checkver(Verdef *def, int vsym, const char *vername, char *strings)
+{
+	vsym &= 0x7fff;
+	for (;;) {
+		if (!(def->vd_flags & VER_FLG_BASE)
+		  && (def->vd_ndx & 0x7fff) == vsym)
+			break;
+		if (def->vd_next == 0)
+			return 0;
+		def = (Verdef *)((char *)def + def->vd_next);
+	}
+	Verdaux *aux = (Verdaux *)((char *)def + def->vd_aux);
+	return !strcmp(vername, strings + aux->vda_name);
+}
+
+#define OK_TYPES (1<<STT_NOTYPE | 1<<STT_OBJECT | 1<<STT_FUNC | 1<<STT_COMMON)
+#define OK_BINDS (1<<STB_GLOBAL | 1<<STB_WEAK | 1<<STB_GNU_UNIQUE)
+
+void *__vdsosym(const char *vername, const char *name)
+{
+	size_t i;
+	for (i=0; libc.auxv[i] != AT_SYSINFO_EHDR; i+=2)
+		if (!libc.auxv[i]) return 0;
+	Ehdr *eh = (void *)libc.auxv[i+1];
+	Phdr *ph = (void *)((char *)eh + eh->e_phoff);
+	size_t *dynv=0, base=-1;
+	for (i=0; i<eh->e_phnum; i++, ph=(void *)((char *)ph+eh->e_phentsize)) {
+		if (ph->p_type == PT_LOAD)
+			base = (size_t)eh + ph->p_offset - ph->p_vaddr;
+		else if (ph->p_type == PT_DYNAMIC)
+			dynv = (void *)((char *)eh + ph->p_offset);
+	}
+	if (!dynv || base==(size_t)-1) return 0;
+
+	char *strings = 0;
+	Sym *syms = 0;
+	uint32_t *hashtab = 0;
+	uint16_t *versym = 0;
+	Verdef *verdef = 0;
+	
+	for (i=0; dynv[i]; i+=2) {
+		void *p = (void *)(base + dynv[i+1]);
+		switch(dynv[i]) {
+		case DT_STRTAB: strings = p; break;
+		case DT_SYMTAB: syms = p; break;
+		case DT_HASH: hashtab = p; break;
+		case DT_VERSYM: versym = p; break;
+		case DT_VERDEF: verdef = p; break;
+		}
+	}	
+
+	if (!strings || !syms || !hashtab) return 0;
+	if (!verdef) versym = 0;
+
+	for (i=0; i<hashtab[1]; i++) {
+		if (!(1<<(syms[i].st_info&0xf) & OK_TYPES)) continue;
+		if (!(1<<(syms[i].st_info>>4) & OK_BINDS)) continue;
+		if (!syms[i].st_shndx) continue;
+		if (strcmp(name, strings+syms[i].st_name)) continue;
+		if (versym && !checkver(verdef, versym[i], vername, strings))
+			continue;
+		return (void *)(base + syms[i].st_value);
+	}
+
+	return 0;
+}
+
+#endif
diff --git a/src/time/clock_gettime.c b/src/time/clock_gettime.c
index ce9f2209..799251d8 100644
--- a/src/time/clock_gettime.c
+++ b/src/time/clock_gettime.c
@@ -3,6 +3,7 @@
 #include <stdint.h>
 #include "syscall.h"
 #include "libc.h"
+#include "atomic.h"
 
 static int sc_clock_gettime(clockid_t clk, struct timespec *ts)
 {
@@ -20,14 +21,21 @@ static int sc_clock_gettime(clockid_t clk, struct timespec *ts)
 	return -1;
 }
 
-weak_alias(sc_clock_gettime, __vdso_clock_gettime);
-
-int (*__cgt)(clockid_t, struct timespec *) = __vdso_clock_gettime;
+void *__vdsosym(const char *, const char *);
 
 int __clock_gettime(clockid_t clk, struct timespec *ts)
 {
-	/* Conditional is to make this work prior to dynamic linking */
-	return __cgt ? __cgt(clk, ts) : sc_clock_gettime(clk, ts);
+#ifdef VDSO_CGT_SYM
+	static int (*cgt)(clockid_t, struct timespec *);
+	if (!cgt) {
+		void *f = __vdsosym(VDSO_CGT_VER, VDSO_CGT_SYM);
+		if (!f) f = (void *)sc_clock_gettime;
+		a_cas_p(&cgt, 0, f);
+	}
+	return cgt(clk, ts);
+#else
+	return sc_clock_gettime(clk, ts);
+#endif
 }
 
 weak_alias(__clock_gettime, clock_gettime);