cmd/go, runtime: always use position-independent code to invoke vsyscall helper on linux/386

golang.org/cl/16346 changed the runtime on linux/386 to invoke the vsyscall
helper via a PIC sequence (CALL 0x10(GS)) when dynamically linking. But it's
actually quite easy to make that code sequence work all the time, so do that,
and remove the ugly machinery that passed the buildmode from the go tool to the
assembly.

This means enlarging m.tls so that we can safely access 0x10(GS) (GS is set to
&m.tls + 4, so 0x10(GS) accesses m_tls[5]).

Change-Id: I1345c34029b149cb5f25320bf19a3cdd73a056fa
Reviewed-on: https://go-review.googlesource.com/16796
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/go/build.go

@@ -332,9 +332,6 @@ func buildModeInit() {
 	_, gccgo := buildToolchain.(gccgoToolchain)
 	var codegenArg string
 	platform := goos + "/" + goarch
-	if buildBuildmode != "default" {
-		buildAsmflags = append(buildAsmflags, "-D=GOBUILDMODE_"+strings.Replace(buildBuildmode, "-", "_", -1)+"=1")
-	}
 	switch buildBuildmode {
 	case "archive":
 		pkgsFilter = pkgsNotMain

src/runtime/runtime2.go

@@ -274,7 +274,7 @@ type m struct {
 	procid        uint64     // for debuggers, but offset not hard-coded
 	gsignal       *g         // signal-handling g
 	sigmask       [4]uintptr // storage for saved signal mask
-	tls           [4]uintptr // thread-local storage (for x86 extern register)
+	tls           [6]uintptr // thread-local storage (for x86 extern register)
 	mstartfn      func()
 	curg          *g       // current running goroutine
 	caughtsig     guintptr // goroutine running during fatal signal

src/runtime/sys_linux_386.s

@@ -10,23 +10,17 @@
 #include "go_tls.h"
 #include "textflag.h"
 
-#ifdef GOBUILDMODE_shared
-#define INVOKE_SYSINFO CALL 0x10(GS)
-#else
-#define INVOKE_SYSINFO CALL *runtime·_vdso(SB)
-#endif
-
 TEXT runtime·exit(SB),NOSPLIT,$0
 	MOVL	$252, AX	// syscall number
 	MOVL	code+0(FP), BX
-	INVOKE_SYSINFO
+	CALL	0x10(GS)
 	INT $3	// not reached
 	RET
 
 TEXT runtime·exit1(SB),NOSPLIT,$0
 	MOVL	$1, AX	// exit - exit the current os thread
 	MOVL	code+0(FP), BX
-	INVOKE_SYSINFO
+	CALL	0x10(GS)
 	INT $3	// not reached
 	RET
 
@@ -35,7 +29,7 @@ TEXT runtime·open(SB),NOSPLIT,$0
 	MOVL	name+0(FP), BX
 	MOVL	mode+4(FP), CX
 	MOVL	perm+8(FP), DX
-	INVOKE_SYSINFO
+	CALL	0x10(GS)
 	CMPL	AX, $0xfffff001
 	JLS	2(PC)
 	MOVL	$-1, AX
@@ -45,7 +39,7 @@ TEXT runtime·open(SB),NOSPLIT,$0
 TEXT runtime·closefd(SB),NOSPLIT,$0
 	MOVL	$6, AX		// syscall - close
 	MOVL	fd+0(FP), BX
-	INVOKE_SYSINFO
+	CALL	0x10(GS)
 	CMPL	AX, $0xfffff001
 	JLS	2(PC)
 	MOVL	$-1, AX
@@ -57,7 +51,7 @@ TEXT runtime·write(SB),NOSPLIT,$0
 	MOVL	fd+0(FP), BX
 	MOVL	p+4(FP), CX
 	MOVL	n+8(FP), DX
-	INVOKE_SYSINFO
+	CALL	0x10(GS)
 	CMPL	AX, $0xfffff001
 	JLS	2(PC)
 	MOVL	$-1, AX
@@ -69,7 +63,7 @@ TEXT runtime·read(SB),NOSPLIT,$0
 	MOVL	fd+0(FP), BX
 	MOVL	p+4(FP), CX
 	MOVL	n+8(FP), DX
-	INVOKE_SYSINFO
+	CALL	0x10(GS)
 	CMPL	AX, $0xfffff001
 	JLS	2(PC)
 	MOVL	$-1, AX
@@ -80,7 +74,7 @@ TEXT runtime·getrlimit(SB),NOSPLIT,$0
 	MOVL	$191, AX		// syscall - ugetrlimit
 	MOVL	kind+0(FP), BX
 	MOVL	limit+4(FP), CX
-	INVOKE_SYSINFO
+	CALL	0x10(GS)
 	MOVL	AX, ret+8(FP)
 	RET
 
@@ -99,31 +93,31 @@ TEXT runtime·usleep(SB),NOSPLIT,$8
 	MOVL	$0, DX
 	MOVL	$0, SI
 	LEAL	0(SP), DI
-	INVOKE_SYSINFO
+	CALL	0x10(GS)
 	RET
 
 TEXT runtime·gettid(SB),NOSPLIT,$0-4
 	MOVL	$224, AX	// syscall - gettid
-	INVOKE_SYSINFO
+	CALL	0x10(GS)
 	MOVL	AX, ret+0(FP)
 	RET
 
 TEXT runtime·raise(SB),NOSPLIT,$12
 	MOVL	$224, AX	// syscall - gettid
-	INVOKE_SYSINFO
+	CALL	0x10(GS)
 	MOVL	AX, BX	// arg 1 tid
 	MOVL	sig+0(FP), CX	// arg 2 signal
 	MOVL	$238, AX	// syscall - tkill
-	INVOKE_SYSINFO
+	CALL	0x10(GS)
 	RET
 
 TEXT runtime·raiseproc(SB),NOSPLIT,$12
 	MOVL	$20, AX	// syscall - getpid
-	INVOKE_SYSINFO
+	CALL	0x10(GS)
 	MOVL	AX, BX	// arg 1 pid
 	MOVL	sig+0(FP), CX	// arg 2 signal
 	MOVL	$37, AX	// syscall - kill
-	INVOKE_SYSINFO
+	CALL	0x10(GS)
 	RET
 
 TEXT runtime·setitimer(SB),NOSPLIT,$0-12
@@ -131,7 +125,7 @@ TEXT runtime·setitimer(SB),NOSPLIT,$0-12
 	MOVL	mode+0(FP), BX
 	MOVL	new+4(FP), CX
 	MOVL	old+8(FP), DX
-	INVOKE_SYSINFO
+	CALL	0x10(GS)
 	RET
 
 TEXT runtime·mincore(SB),NOSPLIT,$0-16
@@ -139,7 +133,7 @@ TEXT runtime·mincore(SB),NOSPLIT,$0-16
 	MOVL	addr+0(FP), BX
 	MOVL	n+4(FP), CX
 	MOVL	dst+8(FP), DX
-	INVOKE_SYSINFO
+	CALL	0x10(GS)
 	MOVL	AX, ret+12(FP)
 	RET
 
@@ -149,7 +143,7 @@ TEXT time·now(SB), NOSPLIT, $32
 	MOVL	$0, BX		// CLOCK_REALTIME
 	LEAL	8(SP), CX
 	MOVL	$0, DX
-	INVOKE_SYSINFO
+	CALL	0x10(GS)
 	MOVL	8(SP), AX	// sec
 	MOVL	12(SP), BX	// nsec
 
@@ -166,7 +160,7 @@ TEXT runtime·nanotime(SB), NOSPLIT, $32
 	MOVL	$1, BX		// CLOCK_MONOTONIC
 	LEAL	8(SP), CX
 	MOVL	$0, DX
-	INVOKE_SYSINFO
+	CALL	0x10(GS)
 	MOVL	8(SP), AX	// sec
 	MOVL	12(SP), BX	// nsec
 
@@ -187,7 +181,7 @@ TEXT runtime·rtsigprocmask(SB),NOSPLIT,$0
 	MOVL	new+4(FP), CX
 	MOVL	old+8(FP), DX
 	MOVL	size+12(FP), SI
-	INVOKE_SYSINFO
+	CALL	0x10(GS)
 	CMPL	AX, $0xfffff001
 	JLS	2(PC)
 	INT $3
@@ -199,7 +193,7 @@ TEXT runtime·rt_sigaction(SB),NOSPLIT,$0
 	MOVL	new+4(FP), CX
 	MOVL	old+8(FP), DX
 	MOVL	size+12(FP), SI
-	INVOKE_SYSINFO
+	CALL	0x10(GS)
 	MOVL	AX, ret+16(FP)
 	RET
 
@@ -227,9 +221,9 @@ TEXT runtime·sigtramp(SB),NOSPLIT,$12
 TEXT runtime·sigreturn(SB),NOSPLIT,$0
 	MOVL	$173, AX	// rt_sigreturn
 	// Sigreturn expects same SP as signal handler,
-	// so cannot CALL *runtime._vsdo(SB) here.
+	// so cannot CALL 0x10(GS) here.
 	INT	$0x80
-	INT $3	// not reached
+	INT	$3	// not reached
 	RET
 
 TEXT runtime·mmap(SB),NOSPLIT,$0
@@ -241,7 +235,7 @@ TEXT runtime·mmap(SB),NOSPLIT,$0
 	MOVL	fd+16(FP), DI
 	MOVL	off+20(FP), BP
 	SHRL	$12, BP
-	INVOKE_SYSINFO
+	CALL	0x10(GS)
 	CMPL	AX, $0xfffff001
 	JLS	3(PC)
 	NOTL	AX
@@ -253,7 +247,7 @@ TEXT runtime·munmap(SB),NOSPLIT,$0
 	MOVL	$91, AX	// munmap
 	MOVL	addr+0(FP), BX
 	MOVL	n+4(FP), CX
-	INVOKE_SYSINFO
+	CALL	0x10(GS)
 	CMPL	AX, $0xfffff001
 	JLS	2(PC)
 	INT $3
@@ -264,7 +258,7 @@ TEXT runtime·madvise(SB),NOSPLIT,$0
 	MOVL	addr+0(FP), BX
 	MOVL	n+4(FP), CX
 	MOVL	flags+8(FP), DX
-	INVOKE_SYSINFO
+	CALL	0x10(GS)
 	// ignore failure - maybe pages are locked
 	RET
 
@@ -278,7 +272,7 @@ TEXT runtime·futex(SB),NOSPLIT,$0
 	MOVL	ts+12(FP), SI
 	MOVL	addr2+16(FP), DI
 	MOVL	val3+20(FP), BP
-	INVOKE_SYSINFO
+	CALL	0x10(GS)
 	MOVL	AX, ret+24(FP)
 	RET
 
@@ -300,10 +294,9 @@ TEXT runtime·clone(SB),NOSPLIT,$0
 	MOVL	SI, 8(CX)
 	MOVL	$1234, 12(CX)
 
-	// cannot use CALL *runtime·_vdso(SB) here, because
+	// cannot use CALL 0x10(GS) here, because the stack changes during the
-	// the stack changes during the system call (after
+	// system call (after CALL 0x10(GS), the child is still using the
-	// CALL *runtime·_vdso(SB), the child is still using
+	// parent's stack when executing its RET instruction).
-	// the parent's stack when executing its RET instruction).
 	INT	$0x80
 
 	// In parent, return.
@@ -320,7 +313,7 @@ TEXT runtime·clone(SB),NOSPLIT,$0
 
 	// Initialize AX to Linux tid
 	MOVL	$224, AX
-	INVOKE_SYSINFO
+	CALL	0x10(GS)
 
 	MOVL	0(SP), BX	    // m
 	MOVL	4(SP), DX	    // g
@@ -371,7 +364,7 @@ TEXT runtime·sigaltstack(SB),NOSPLIT,$-8
 	MOVL	$186, AX	// sigaltstack
 	MOVL	new+4(SP), BX
 	MOVL	old+8(SP), CX
-	INVOKE_SYSINFO
+	CALL	0x10(GS)
 	CMPL	AX, $0xfffff001
 	JLS	2(PC)
 	INT	$3
@@ -429,6 +422,12 @@ TEXT runtime·setldt(SB),NOSPLIT,$32
 	ADDL	$0x4, CX	// address
 	MOVL	CX, 0(CX)
 #endif
+        // We copy the dynamic linker behaviour of storing the vsyscall entry point
+        // at 0x10(GS) so that it can be invoked by "CALL 0x10(GS)" in all
+        // situations, not only those where the binary is actually dynamically
+        // linked.
+	MOVL	runtime·_vdso(SB), AX
+	MOVL	AX, 0x10(CX)
 
 	// set up user_desc
 	LEAL	16(SP), AX	// struct user_desc
@@ -442,7 +441,8 @@ TEXT runtime·setldt(SB),NOSPLIT,$32
 	MOVL	AX, CX	// user_desc
 	MOVL	$16, DX	// sizeof(user_desc)
 	MOVL	$123, AX	// syscall - modify_ldt
-	INVOKE_SYSINFO
+	// We can't call this via 0x10(GS) because this is called from setldt0 to set that up.
+	INT     $0x80
 
 	// breakpoint on error
 	CMPL AX, $0xfffff001
@@ -459,7 +459,7 @@ TEXT runtime·setldt(SB),NOSPLIT,$32
 
 TEXT runtime·osyield(SB),NOSPLIT,$0
 	MOVL	$158, AX
-	INVOKE_SYSINFO
+	CALL	0x10(GS)
 	RET
 
 TEXT runtime·sched_getaffinity(SB),NOSPLIT,$0
@@ -467,7 +467,7 @@ TEXT runtime·sched_getaffinity(SB),NOSPLIT,$0
 	MOVL	pid+0(FP), BX
 	MOVL	len+4(FP), CX
 	MOVL	buf+8(FP), DX
-	INVOKE_SYSINFO
+	CALL	0x10(GS)
 	MOVL	AX, ret+12(FP)
 	RET
 
@@ -475,7 +475,7 @@ TEXT runtime·sched_getaffinity(SB),NOSPLIT,$0
 TEXT runtime·epollcreate(SB),NOSPLIT,$0
 	MOVL    $254, AX
 	MOVL	size+0(FP), BX
-	INVOKE_SYSINFO
+	CALL	0x10(GS)
 	MOVL	AX, ret+4(FP)
 	RET
 
@@ -483,7 +483,7 @@ TEXT runtime·epollcreate(SB),NOSPLIT,$0
 TEXT runtime·epollcreate1(SB),NOSPLIT,$0
 	MOVL    $329, AX
 	MOVL	flags+0(FP), BX
-	INVOKE_SYSINFO
+	CALL	0x10(GS)
 	MOVL	AX, ret+4(FP)
 	RET
 
@@ -494,7 +494,7 @@ TEXT runtime·epollctl(SB),NOSPLIT,$0
 	MOVL	op+4(FP), CX
 	MOVL	fd+8(FP), DX
 	MOVL	ev+12(FP), SI
-	INVOKE_SYSINFO
+	CALL	0x10(GS)
 	MOVL	AX, ret+16(FP)
 	RET
 
@@ -505,7 +505,7 @@ TEXT runtime·epollwait(SB),NOSPLIT,$0
 	MOVL	ev+4(FP), CX
 	MOVL	nev+8(FP), DX
 	MOVL	timeout+12(FP), SI
-	INVOKE_SYSINFO
+	CALL	0x10(GS)
 	MOVL	AX, ret+16(FP)
 	RET
 
@@ -515,7 +515,7 @@ TEXT runtime·closeonexec(SB),NOSPLIT,$0
 	MOVL	fd+0(FP), BX  // fd
 	MOVL	$2, CX  // F_SETFD
 	MOVL	$1, DX  // FD_CLOEXEC
-	INVOKE_SYSINFO
+	CALL	0x10(GS)
 	RET
 
 // int access(const char *name, int mode)
@@ -523,7 +523,7 @@ TEXT runtime·access(SB),NOSPLIT,$0
 	MOVL	$33, AX  // syscall - access
 	MOVL	name+0(FP), BX
 	MOVL	mode+4(FP), CX
-	INVOKE_SYSINFO
+	CALL	0x10(GS)
 	MOVL	AX, ret+8(FP)
 	RET
 
@@ -534,7 +534,7 @@ TEXT runtime·connect(SB),NOSPLIT,$0-16
 	MOVL	$102, AX  // syscall - socketcall
 	MOVL	$3, BX  // connect
 	LEAL	fd+0(FP), CX
-	INVOKE_SYSINFO
+	CALL	0x10(GS)
 	MOVL	AX, ret+12(FP)
 	RET
 
@@ -545,6 +545,6 @@ TEXT runtime·socket(SB),NOSPLIT,$0-16
 	MOVL	$102, AX  // syscall - socketcall
 	MOVL	$1, BX  // socket
 	LEAL	domain+0(FP), CX
-	INVOKE_SYSINFO
+	CALL	0x10(GS)
 	MOVL	AX, ret+12(FP)
 	RET