cmd,runtime: TLS setup for android/386

Same ugly hack as https://go-review.googlesource.com/15991.

Update golang/go#9327.

Change-Id: I58284e83268a15de95eabc833c3e01bf1e3faa2e
Reviewed-on: https://go-review.googlesource.com/16678Reviewed-by: David Crawshaw <crawshaw@golang.org>

src/cmd/internal/obj/x86/asm6.go

@@ -1975,6 +1975,9 @@ func prefixof(ctxt *obj.Link, p *obj.Prog, a *obj.Addr) int {
 			if p.Mode == 32 {
 				switch ctxt.Headtype {
 				default:
+					if isAndroid {
+						return 0x65 // GS
+					}
 					log.Fatalf("unknown TLS base register for %s", obj.Headstr(ctxt.Headtype))
 
 				case obj.Hdarwin,

src/cmd/link/internal/ld/sym.go

@@ -102,10 +102,18 @@ func linknew(arch *LinkArch) *Link {
 		obj.Hopenbsd,
 		obj.Hdragonfly,
 		obj.Hsolaris:
-		if obj.Getgoos() == "android" && ctxt.Arch.Thechar == '6' {
-			// Android/x86 constant - offset from 0(FS) to our
-			// TLS slot. Explained in src/runtime/cgo/gcc_android_*.c
-			ctxt.Tlsoffset = 0x1d0
+		if obj.Getgoos() == "android" {
+			switch ctxt.Arch.Thechar {
+			case '6':
+				// Android/amd64 constant - offset from 0(FS) to our TLS slot.
+				// Explained in src/runtime/cgo/gcc_android_*.c
+				ctxt.Tlsoffset = 0x1d0
+			case '8':
+				// Android/386 constant - offset from 0(GS) to our TLS slot.
+				ctxt.Tlsoffset = 0xf8
+			default:
+				ctxt.Tlsoffset = -1 * ctxt.Arch.Ptrsize
+			}
 		} else {
 			ctxt.Tlsoffset = -1 * ctxt.Arch.Ptrsize
 		}

src/runtime/cgo/gcc_android_386.c

+// Copyright 2015 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+#include <string.h> /* for strerror */
+#include <pthread.h>
+#include <signal.h>
+#include "libcgo.h"
+
+static void* threadentry(void*);
+static pthread_key_t k1;
+
+#define magic1 (0x23581321U)
+
+static void
+inittls(void)
+{
+	uint32 x;
+	pthread_key_t tofree[128], k;
+	int i, ntofree;
+
+	/*
+	 * Same logic, code as gcc_android_amd64.c:/inittls.
+	 * Note that this is a temporary hack that should be fixed soon.
+	 *
+	 * TODO: fix this.
+	 *
+	 * The linker and runtime hard-code this constant offset
+	 * from %gs where we expect to find g. Disgusting.
+	 *
+	 * Known to src/cmd/link/internal/ld/sym.go:/0xf8
+	 * and to src/runtime/sys_linux_386.s:/0xf8 or /GOOS_android.
+	 * TODO(hyangah): check 0xb0 works with API23+
+	 *
+	 * As disgusting as on the darwin/386, darwin/amd64.
+	 */
+	ntofree = 0;
+	for(;;) {
+		if(pthread_key_create(&k, nil) < 0) {
+			fprintf(stderr, "runtime/cgo: pthread_key_create failed\n");
+			abort();
+		}
+		pthread_setspecific(k, (void*)magic1);
+		asm volatile("movl %%gs:0xf8, %0" : "=r"(x));
+		pthread_setspecific(k, 0);
+		if (x == magic1) {
+			k1 = k;
+			break;
+		}
+		if(ntofree >= nelem(tofree)) {
+			fprintf(stderr, "runtime/cgo: could not obtain pthread_keys\n");
+			fprintf(stderr, "\ttried");
+			for(i=0; i<ntofree; i++)
+				fprintf(stderr, " %#x", (unsigned)tofree[i]);
+			fprintf(stderr, "\n");
+			abort();
+		}
+		tofree[ntofree++] = k;
+	}
+	// TODO: output to stderr is not useful for apps.
+	// Can we fall back to Android's log library?
+
+	/*
+	 * We got the key we wanted.  Free the others.
+	 */
+	for(i=0; i<ntofree; i++) {
+		pthread_key_delete(tofree[i]);
+	}
+}
+
+
+static void*
+threadentry(void *v)
+{
+	ThreadStart ts;
+
+	ts = *(ThreadStart*)v;
+	free(v);
+
+	pthread_setspecific(k1, (void*)ts.g);
+
+	crosscall_386(ts.fn);
+	return nil;
+}
+
+void (*x_cgo_inittls)(void) = inittls;
+void* (*x_cgo_threadentry)(void*) = threadentry;

src/runtime/cgo/gcc_linux_386.c

@@ -10,6 +10,10 @@
 static void *threadentry(void*);
 static void (*setg_gcc)(void*);
 
+// These will be set in gcc_android_386.c for android-specific customization.
+void (*x_cgo_inittls)(void);
+void* (*x_cgo_threadentry)(void*);
+
 void
 x_cgo_init(G *g, void (*setg)(void*))
 {
@@ -21,6 +25,10 @@ x_cgo_init(G *g, void (*setg)(void*))
 	pthread_attr_getstacksize(&attr, &size);
 	g->stacklo = (uintptr)&attr - size + 4096;
 	pthread_attr_destroy(&attr);
+
+	if (x_cgo_inittls) {
+		x_cgo_inittls();
+	}
 }
 
 
@@ -57,6 +65,10 @@ _cgo_sys_thread_start(ThreadStart *ts)
 static void*
 threadentry(void *v)
 {
+	if (x_cgo_threadentry) {
+		return x_cgo_threadentry(v);
+	}
+
 	ThreadStart ts;
 
 	ts = *(ThreadStart*)v;

src/runtime/rt0_android_386.s

+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+#include "textflag.h"
+
+TEXT _rt0_386_android(SB),NOSPLIT,$8
+	MOVL	8(SP), AX  // argc
+	LEAL	12(SP), BX  // argv
+	MOVL	AX, 0(SP)
+	MOVL	BX, 4(SP)
+	CALL	main(SB)
+	INT	$3
+
+TEXT _rt0_386_android_lib(SB),NOSPLIT,$0
+	PUSHL	$_rt0_386_android_argv(SB)  // argv
+	PUSHL	$1  // argc
+	CALL	_rt0_386_linux_lib(SB)
+	POPL	AX
+	POPL	AX
+	RET
+
+DATA _rt0_386_android_argv+0x00(SB)/4,$_rt0_386_android_argv0(SB)
+DATA _rt0_386_android_argv+0x04(SB)/4,$0  // argv terminate
+DATA _rt0_386_android_argv+0x08(SB)/4,$0  // envp terminate
+DATA _rt0_386_android_argv+0x0c(SB)/4,$0  // auxv terminate
+GLOBL _rt0_386_android_argv(SB),NOPTR,$0x10
+
+// TODO: wire up necessary VDSO (see os_linux_386.go)
+
+DATA _rt0_386_android_argv0(SB)/8, $"gojni"
+GLOBL _rt0_386_android_argv0(SB),RODATA,$8

src/runtime/sys_linux_386.s

@@ -405,6 +405,15 @@ TEXT runtime·setldt(SB),NOSPLIT,$32
 	MOVL	entry+0(FP), BX	// entry
 	MOVL	address+4(FP), CX	// base address
 
+#ifdef GOOS_android
+	/*
+	 * Same as in sys_darwin_386.s:/ugliness, different constant.
+	 * address currently holds m->tls, which must be %gs:0xf8.
+	 * See cgo/gcc_android_386.c for the derivation of the constant.
+	 */
+	SUBL	$0xf8, CX
+	MOVL	CX, 0(CX)
+#else
 	/*
 	 * When linking against the system libraries,
 	 * we use its pthread_create and let it set up %gs
@@ -420,6 +429,7 @@ TEXT runtime·setldt(SB),NOSPLIT,$32
 	 */
 	ADDL	$0x4, CX	// address
 	MOVL	CX, 0(CX)
+#endif
 
 	// set up user_desc
 	LEAL	16(SP), AX	// struct user_desc