runtime: parse auxv for page size and executable name on Solaris

Decode AT_PAGESZ to determine physPageSize and AT_SUN_EXECNAME for
os.Executable.

Change-Id: I6ff774ad9d76c68fc61eb307df58217c17fd578d
Reviewed-on: https://go-review.googlesource.com/104375
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/os/executable_solaris.go

@@ -6,12 +6,17 @@ package os
 
 import "syscall"
 
+var executablePath string // set by sysauxv in ../runtime/os3_solaris.go
+
 var initCwd, initCwdErr = Getwd()
 
 func executable() (string, error) {
-	path, err := syscall.Getexecname()
-	if err != nil {
-		return path, err
+	path := executablePath
+	if len(path) == 0 {
+		path, err := syscall.Getexecname()
+		if err != nil {
+			return path, err
+		}
 	}
 	if len(path) > 0 && path[0] != '/' {
 		if initCwdErr != nil {

src/runtime/auxv_none.go

@@ -7,6 +7,7 @@
 // +build !dragonfly
 // +build !freebsd
 // +build !netbsd
+// +build !solaris
 
 package runtime
 

src/runtime/os3_solaris.go

@@ -4,7 +4,10 @@
 
 package runtime
 
-import "unsafe"
+import (
+	"runtime/internal/sys"
+	"unsafe"
+)
 
 //go:cgo_export_dynamic runtime.end _end
 //go:cgo_export_dynamic runtime.etext _etext
@@ -128,7 +131,9 @@ func getPageSize() uintptr {
 
 func osinit() {
 	ncpu = getncpu()
-	physPageSize = getPageSize()
+	if physPageSize == 0 {
+		physPageSize = getPageSize()
+	}
 }
 
 func tstart_sysvicall(newm *m) uint32
@@ -509,3 +514,40 @@ func osyield() {
 	}
 	osyield1()
 }
+
+//go:linkname executablePath os.executablePath
+var executablePath string
+
+func sysargs(argc int32, argv **byte) {
+	n := argc + 1
+
+	// skip over argv, envp to get to auxv
+	for argv_index(argv, n) != nil {
+		n++
+	}
+
+	// skip NULL separator
+	n++
+
+	// now argv+n is auxv
+	auxv := (*[1 << 28]uintptr)(add(unsafe.Pointer(argv), uintptr(n)*sys.PtrSize))
+	sysauxv(auxv[:])
+}
+
+const (
+	_AT_NULL         = 0    // Terminates the vector
+	_AT_PAGESZ       = 6    // Page size in bytes
+	_AT_SUN_EXECNAME = 2014 // exec() path name
+)
+
+func sysauxv(auxv []uintptr) {
+	for i := 0; auxv[i] != _AT_NULL; i += 2 {
+		tag, val := auxv[i], auxv[i+1]
+		switch tag {
+		case _AT_PAGESZ:
+			physPageSize = val
+		case _AT_SUN_EXECNAME:
+			executablePath = gostringnocopy((*byte)(unsafe.Pointer(val)))
+		}
+	}
+}