runtime: duplicate code for runtime.nanotime to avoid stack overflow in vDSO clock_ge...

Fixes #4402.

R=remyoudompheng, shivakumar.gn, random0x00, rsc
CC=golang-dev
https://golang.org/cl/6842063

diff --git a/src/pkg/runtime/sys_linux_amd64.s b/src/pkg/runtime/sys_linux_amd64.s
index cb6f4a8ca0ed19f1f896bda3c56aad57efea2085..e8078158c6464e49d3aa8f0194f039c2157c14a5 100644 (file)
--- a/src/pkg/runtime/sys_linux_amd64.s
+++ b/src/pkg/runtime/sys_linux_amd64.s
@@ -101,36 +101,59 @@ TEXT runtime·mincore(SB),7,$0-24
        RET
 
 // func now() (sec int64, nsec int32)
-TEXT time·now(SB), 7, $32
+TEXT time·now(SB),7,$16
+       // Be careful. We're calling a function with gcc calling convention here.
+       // We're guaranteed 128 bytes on entry, and we've taken 16, and the
+       // call uses another 8.
+       // That leaves 104 for the gettime code to use. Hope that's enough!
        MOVQ    runtime·__vdso_clock_gettime_sym(SB), AX
        CMPQ    AX, $0
        JEQ     fallback_gtod
        MOVL    $0, DI // CLOCK_REALTIME
-       LEAQ    8(SP), SI
+       LEAQ    0(SP), SI
        CALL    AX
-       MOVQ    8(SP), AX       // sec
-       MOVQ    16(SP), DX      // nsec
+       MOVQ    0(SP), AX       // sec
+       MOVQ    8(SP), DX       // nsec
        MOVQ    AX, sec+0(FP)
        MOVL    DX, nsec+8(FP)
        RET
 fallback_gtod:
-       LEAQ    8(SP), DI
+       LEAQ    0(SP), DI
        MOVQ    $0, SI
        MOVQ    runtime·__vdso_gettimeofday_sym(SB), AX
        CALL    AX
-       MOVQ    8(SP), AX       // sec
-       MOVL    16(SP), DX      // usec
+       MOVQ    0(SP), AX       // sec
+       MOVL    8(SP), DX       // usec
        IMULQ   $1000, DX
        MOVQ    AX, sec+0(FP)
        MOVL    DX, nsec+8(FP)
        RET
 
-TEXT runtime·nanotime(SB), 7, $32
-       CALL    time·now(SB)
+TEXT runtime·nanotime(SB),7,$16
+       // Duplicate time.now here to avoid using up precious stack space.
+       // See comment above in time.now.
+       MOVQ    runtime·__vdso_clock_gettime_sym(SB), AX
+       CMPQ    AX, $0
+       JEQ     fallback_gtod_nt
+       MOVL    $0, DI // CLOCK_REALTIME
+       LEAQ    0(SP), SI
+       CALL    AX
        MOVQ    0(SP), AX       // sec
-       MOVL    8(SP), DX       // nsec
-
-       // sec is in AX, usec in DX
+       MOVQ    8(SP), DX       // nsec
+       // sec is in AX, nsec in DX
+       // return nsec in AX
+       IMULQ   $1000000000, AX
+       ADDQ    DX, AX
+       RET
+fallback_gtod_nt:
+       LEAQ    0(SP), DI
+       MOVQ    $0, SI
+       MOVQ    runtime·__vdso_gettimeofday_sym(SB), AX
+       CALL    AX
+       MOVQ    0(SP), AX       // sec
+       MOVL    8(SP), DX       // usec
+       IMULQ   $1000, DX
+       // sec is in AX, nsec in DX
        // return nsec in AX
        IMULQ   $1000000000, AX
        ADDQ    DX, AX