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runtime: remove unnecessary writes to gp.sched.g

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A g's sched.g is set in newproc1:

	newg.sched.g = guintptr(unsafe.Pointer(newg))

After that, it never changes. Yet lots of assembly code does
"g.sched.g = g" unnecessarily. Remove all those lines to avoid
confusion about whether it ever changes.

Also, split gogo into two functions, one that does the nil g check
and a second that does the actual switch. This way, if the nil g check
fails, we get a stack trace showing the call stack that led to the failure.
(The SP write would otherwise cause the stack trace to abort.)

Also restore the proper nil g check in a handful of assembly functions.
(There is little point in checking for nil g *after* installing it as the real g.)

Change-Id: I22866b093f901f765de1d074e36eeec10366abfb
Reviewed-on: https://go-review.googlesource.com/c/go/+/292109
Trust: Russ Cox <rsc@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
This commit is contained in:
Russ Cox 2021-02-15 09:25:55 -05:00
parent 6fe8981620
commit aa0388f2ed
11 changed files with 78 additions and 57 deletions
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7
src/runtime/asm_386.s
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@ -275,10 +275,13 @@ TEXT runtime·asminit(SB),NOSPLIT,$0-0
// void gogo(Gobuf*)
// restore state from Gobuf; longjmp
TEXT runtime·gogo(SB), NOSPLIT, $8-4
TEXT runtime·gogo(SB), NOSPLIT, $0-4
MOVL buf+0(FP), BX // gobuf
MOVL gobuf_g(BX), DX
MOVL 0(DX), CX // make sure g != nil
JMP gogo<>(SB)
TEXT gogo<>(SB), NOSPLIT, $0
get_tls(CX)
MOVL DX, g(CX)
MOVL gobuf_sp(BX), SP // restore SP
@ -303,7 +306,6 @@ TEXT runtime·mcall(SB), NOSPLIT, $0-4
MOVL BX, (g_sched+gobuf_pc)(AX)
LEAL fn+0(FP), BX // caller's SP
MOVL BX, (g_sched+gobuf_sp)(AX)
MOVL AX, (g_sched+gobuf_g)(AX)
// switch to m->g0 & its stack, call fn
MOVL g(DX), BX
@ -432,7 +434,6 @@ TEXT runtime·morestack(SB),NOSPLIT,$0-0
// Set g->sched to context in f.
MOVL 0(SP), AX // f's PC
MOVL AX, (g_sched+gobuf_pc)(SI)
MOVL SI, (g_sched+gobuf_g)(SI)
LEAL 4(SP), AX // f's SP
MOVL AX, (g_sched+gobuf_sp)(SI)
MOVL DX, (g_sched+gobuf_ctxt)(SI)

7
src/runtime/asm_amd64.s
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@ -256,10 +256,13 @@ TEXT runtime·asminit(SB),NOSPLIT,$0-0
// func gogo(buf *gobuf)
// restore state from Gobuf; longjmp
TEXT runtime·gogo(SB), NOSPLIT, $16-8
TEXT runtime·gogo(SB), NOSPLIT, $0-8
MOVQ buf+0(FP), BX // gobuf
MOVQ gobuf_g(BX), DX
MOVQ 0(DX), CX // make sure g != nil
JMP gogo<>(SB)
TEXT gogo<>(SB), NOSPLIT, $0
get_tls(CX)
MOVQ DX, g(CX)
MOVQ DX, R14 // set the g register
@ -287,7 +290,6 @@ TEXT runtime·mcall(SB), NOSPLIT, $0-8
MOVQ BX, (g_sched+gobuf_pc)(AX)
LEAQ fn+0(FP), BX // caller's SP
MOVQ BX, (g_sched+gobuf_sp)(AX)
MOVQ AX, (g_sched+gobuf_g)(AX)
MOVQ BP, (g_sched+gobuf_bp)(AX)
// switch to m->g0 & its stack, call fn
@ -418,7 +420,6 @@ TEXT runtime·morestack(SB),NOSPLIT,$0-0
// Set g->sched to context in f.
MOVQ 0(SP), AX // f's PC
MOVQ AX, (g_sched+gobuf_pc)(SI)
MOVQ SI, (g_sched+gobuf_g)(SI)
LEAQ 8(SP), AX // f's SP
MOVQ AX, (g_sched+gobuf_sp)(SI)
MOVQ BP, (g_sched+gobuf_bp)(SI)

19
src/runtime/asm_arm.s
View File

@ -208,21 +208,14 @@ TEXT runtime·asminit(SB),NOSPLIT,$0-0
// void gogo(Gobuf*)
// restore state from Gobuf; longjmp
TEXT runtime·gogo(SB),NOSPLIT,$8-4
TEXT runtime·gogo(SB),NOSPLIT|NOFRAME,$0-4
MOVW buf+0(FP), R1
MOVW gobuf_g(R1), R0
BL setg<>(SB)
MOVW 0(R0), R2 // make sure g != nil
B gogo<>(SB)
// NOTE: We updated g above, and we are about to update SP.
// Until LR and PC are also updated, the g/SP/LR/PC quadruple
// are out of sync and must not be used as the basis of a traceback.
// Sigprof skips the traceback when SP is not within g's bounds,
// and when the PC is inside this function, runtime.gogo.
// Since we are about to update SP, until we complete runtime.gogo
// we must not leave this function. In particular, no calls
// after this point: it must be straight-line code until the
// final B instruction.
// See large comment in sigprof for more details.
TEXT gogo<>(SB),NOSPLIT|NOFRAME,$0
BL setg<>(SB)
MOVW gobuf_sp(R1), R13 // restore SP==R13
MOVW gobuf_lr(R1), LR
MOVW gobuf_ret(R1), R0
@ -246,7 +239,6 @@ TEXT runtime·mcall(SB),NOSPLIT|NOFRAME,$0-4
MOVW LR, (g_sched+gobuf_pc)(g)
MOVW $0, R11
MOVW R11, (g_sched+gobuf_lr)(g)
MOVW g, (g_sched+gobuf_g)(g)
// Switch to m->g0 & its stack, call fn.
MOVW g, R1
@ -537,7 +529,6 @@ TEXT gosave_systemstack_switch<>(SB),NOSPLIT|NOFRAME,$0
ADD $4, R11 // get past push {lr}
MOVW R11, (g_sched+gobuf_pc)(g)
MOVW R13, (g_sched+gobuf_sp)(g)
MOVW g, (g_sched+gobuf_g)(g)
MOVW $0, R11
MOVW R11, (g_sched+gobuf_lr)(g)
MOVW R11, (g_sched+gobuf_ret)(g)

12
src/runtime/asm_arm64.s
View File

@ -115,12 +115,16 @@ TEXT runtime·asminit(SB),NOSPLIT|NOFRAME,$0-0
// void gogo(Gobuf*)
// restore state from Gobuf; longjmp
TEXT runtime·gogo(SB), NOSPLIT, $24-8
TEXT runtime·gogo(SB), NOSPLIT|NOFRAME, $0-8
MOVD buf+0(FP), R5
MOVD gobuf_g(R5), g
MOVD gobuf_g(R5), R6
MOVD 0(R6), R4 // make sure g != nil
B gogo<>(SB)
TEXT gogo<>(SB), NOSPLIT|NOFRAME, $0
MOVD R6, g
BL runtime·save_g(SB)
MOVD 0(g), R4 // make sure g is not nil
MOVD gobuf_sp(R5), R0
MOVD R0, RSP
MOVD gobuf_bp(R5), R29
@ -147,7 +151,6 @@ TEXT runtime·mcall(SB), NOSPLIT|NOFRAME, $0-8
MOVD R29, (g_sched+gobuf_bp)(g)
MOVD LR, (g_sched+gobuf_pc)(g)
MOVD $0, (g_sched+gobuf_lr)(g)
MOVD g, (g_sched+gobuf_g)(g)
// Switch to m->g0 & its stack, call fn.
MOVD g, R3
@ -861,7 +864,6 @@ TEXT gosave_systemstack_switch<>(SB),NOSPLIT|NOFRAME,$0
MOVD R29, (g_sched+gobuf_bp)(g)
MOVD $0, (g_sched+gobuf_lr)(g)
MOVD $0, (g_sched+gobuf_ret)(g)
MOVD g, (g_sched+gobuf_g)(g)
// Assert ctxt is zero. See func save.
MOVD (g_sched+gobuf_ctxt)(g), R0
CBZ R0, 2(PC)

11
src/runtime/asm_mips64x.s
View File

@ -91,9 +91,14 @@ TEXT runtime·asminit(SB),NOSPLIT|NOFRAME,$0-0
// void gogo(Gobuf*)
// restore state from Gobuf; longjmp
TEXT runtime·gogo(SB), NOSPLIT, $16-8
TEXT runtime·gogo(SB), NOSPLIT|NOFRAME, $0-8
MOVV buf+0(FP), R3
MOVV gobuf_g(R3), g // make sure g is not nil
MOVV gobuf_g(R3), R4
MOVV 0(R4), R5 // make sure g != nil
JMP gogo<>(SB)
TEXT gogo<>(SB), NOSPLIT|NOFRAME, $0
MOVV R5, g
JAL runtime·save_g(SB)
MOVV 0(g), R2
@ -117,7 +122,6 @@ TEXT runtime·mcall(SB), NOSPLIT|NOFRAME, $0-8
MOVV R29, (g_sched+gobuf_sp)(g)
MOVV R31, (g_sched+gobuf_pc)(g)
MOVV R0, (g_sched+gobuf_lr)(g)
MOVV g, (g_sched+gobuf_g)(g)
// Switch to m->g0 & its stack, call fn.
MOVV g, R1
@ -404,7 +408,6 @@ TEXT gosave_systemstack_switch<>(SB),NOSPLIT|NOFRAME,$0
MOVV R29, (g_sched+gobuf_sp)(g)
MOVV R0, (g_sched+gobuf_lr)(g)
MOVV R0, (g_sched+gobuf_ret)(g)
MOVV g, (g_sched+gobuf_g)(g)
// Assert ctxt is zero. See func save.
MOVV (g_sched+gobuf_ctxt)(g), R1
BEQ R1, 2(PC)

13
src/runtime/asm_mipsx.s
View File

@ -92,12 +92,15 @@ TEXT runtime·asminit(SB),NOSPLIT,$0-0
// void gogo(Gobuf*)
// restore state from Gobuf; longjmp
TEXT runtime·gogo(SB),NOSPLIT,$8-4
TEXT runtime·gogo(SB),NOSPLIT|NOFRAME,$0-4
MOVW buf+0(FP), R3
MOVW gobuf_g(R3), g // make sure g is not nil
JAL runtime·save_g(SB)
MOVW gobuf_g(R3), R4
MOVW 0(R4), R5 // make sure g != nil
JMP gogo<>(SB)
MOVW 0(g), R2
TEXT gogo<>(SB),NOSPLIT|NOFRAME,$0
MOVW R4, g
JAL runtime·save_g(SB)
MOVW gobuf_sp(R3), R29
MOVW gobuf_lr(R3), R31
MOVW gobuf_ret(R3), R1
@ -118,7 +121,6 @@ TEXT runtime·mcall(SB),NOSPLIT|NOFRAME,$0-4
MOVW R29, (g_sched+gobuf_sp)(g)
MOVW R31, (g_sched+gobuf_pc)(g)
MOVW R0, (g_sched+gobuf_lr)(g)
MOVW g, (g_sched+gobuf_g)(g)
// Switch to m->g0 & its stack, call fn.
MOVW g, R1
@ -404,7 +406,6 @@ TEXT gosave_systemstack_switch<>(SB),NOSPLIT|NOFRAME,$0
MOVW R29, (g_sched+gobuf_sp)(g)
MOVW R0, (g_sched+gobuf_lr)(g)
MOVW R0, (g_sched+gobuf_ret)(g)
MOVW g, (g_sched+gobuf_g)(g)
// Assert ctxt is zero. See func save.
MOVW (g_sched+gobuf_ctxt)(g), R1
BEQ R1, 2(PC)

12
src/runtime/asm_ppc64x.s
View File

@ -130,12 +130,16 @@ TEXT runtime·reginit(SB),NOSPLIT|NOFRAME,$0-0
// void gogo(Gobuf*)
// restore state from Gobuf; longjmp
TEXT runtime·gogo(SB), NOSPLIT, $16-8
TEXT runtime·gogo(SB), NOSPLIT|NOFRAME, $0-8
MOVD buf+0(FP), R5
MOVD gobuf_g(R5), g // make sure g is not nil
MOVD gobuf_g(R5), R6
MOVD 0(R6), R4 // make sure g != nil
BR gogo<>(SB)
TEXT gogo<>(SB), NOSPLIT|NOFRAME, $0
MOVD R6, g
BL runtime·save_g(SB)
MOVD 0(g), R4
MOVD gobuf_sp(R5), R1
MOVD gobuf_lr(R5), R31
#ifndef GOOS_aix
@ -163,7 +167,6 @@ TEXT runtime·mcall(SB), NOSPLIT|NOFRAME, $0-8
MOVD LR, R31
MOVD R31, (g_sched+gobuf_pc)(g)
MOVD R0, (g_sched+gobuf_lr)(g)
MOVD g, (g_sched+gobuf_g)(g)
// Switch to m->g0 & its stack, call fn.
MOVD g, R3
@ -536,7 +539,6 @@ TEXT gosave_systemstack_switch<>(SB),NOSPLIT|NOFRAME,$0
MOVD R1, (g_sched+gobuf_sp)(g)
MOVD R0, (g_sched+gobuf_lr)(g)
MOVD R0, (g_sched+gobuf_ret)(g)
MOVD g, (g_sched+gobuf_g)(g)
// Assert ctxt is zero. See func save.
MOVD (g_sched+gobuf_ctxt)(g), R31
CMP R0, R31

12
src/runtime/asm_riscv64.s
View File

@ -224,12 +224,16 @@ TEXT runtime·return0(SB), NOSPLIT, $0
// restore state from Gobuf; longjmp
// func gogo(buf *gobuf)
TEXT runtime·gogo(SB), NOSPLIT, $16-8
TEXT runtime·gogo(SB), NOSPLIT|NOFRAME, $0-8
MOV buf+0(FP), T0
MOV gobuf_g(T0), g // make sure g is not nil
MOV gobuf_g(T0), T1
MOV 0(T1), ZERO // make sure g != nil
JMP gogo<>(SB)
TEXT gogo<>(SB), NOSPLIT|NOFRAME, $0
MOV T1, g
CALL runtime·save_g(SB)
MOV (g), ZERO // make sure g is not nil
MOV gobuf_sp(T0), X2
MOV gobuf_lr(T0), RA
MOV gobuf_ret(T0), A0
@ -270,7 +274,6 @@ TEXT runtime·mcall(SB), NOSPLIT|NOFRAME, $0-8
MOV X2, (g_sched+gobuf_sp)(g)
MOV RA, (g_sched+gobuf_pc)(g)
MOV ZERO, (g_sched+gobuf_lr)(g)
MOV g, (g_sched+gobuf_g)(g)
// Switch to m->g0 & its stack, call fn.
MOV g, T0
@ -300,7 +303,6 @@ TEXT gosave_systemstack_switch<>(SB),NOSPLIT|NOFRAME,$0
MOV X2, (g_sched+gobuf_sp)(g)
MOV ZERO, (g_sched+gobuf_lr)(g)
MOV ZERO, (g_sched+gobuf_ret)(g)
MOV g, (g_sched+gobuf_g)(g)
// Assert ctxt is zero. See func save.
MOV (g_sched+gobuf_ctxt)(g), X31
BEQ ZERO, X31, 2(PC)

11
src/runtime/asm_s390x.s
View File

@ -176,9 +176,14 @@ TEXT runtime·asminit(SB),NOSPLIT|NOFRAME,$0-0
// void gogo(Gobuf*)
// restore state from Gobuf; longjmp
TEXT runtime·gogo(SB), NOSPLIT, $16-8
TEXT runtime·gogo(SB), NOSPLIT|NOFRAME, $0-8
MOVD buf+0(FP), R5
MOVD gobuf_g(R5), g // make sure g is not nil
MOVD gobuf_g(R5), R6
MOVD 0(R6), R7 // make sure g != nil
BR gogo<>(SB)
TEXT gogo<>(SB), NOSPLIT|NOFRAME, $0
MOVD R6, g
BL runtime·save_g(SB)
MOVD 0(g), R4
@ -203,7 +208,6 @@ TEXT runtime·mcall(SB), NOSPLIT, $-8-8
MOVD R15, (g_sched+gobuf_sp)(g)
MOVD LR, (g_sched+gobuf_pc)(g)
MOVD $0, (g_sched+gobuf_lr)(g)
MOVD g, (g_sched+gobuf_g)(g)
// Switch to m->g0 & its stack, call fn.
MOVD g, R3
@ -500,7 +504,6 @@ TEXT gosave_systemstack_switch<>(SB),NOSPLIT|NOFRAME,$0
MOVD R15, (g_sched+gobuf_sp)(g)
MOVD $0, (g_sched+gobuf_lr)(g)
MOVD $0, (g_sched+gobuf_ret)(g)
MOVD g, (g_sched+gobuf_g)(g)
// Assert ctxt is zero. See func save.
MOVD (g_sched+gobuf_ctxt)(g), R1
CMPBEQ R1, $0, 2(PC)

7
src/runtime/asm_wasm.s
View File

@ -34,7 +34,9 @@ TEXT ·checkASM(SB), NOSPLIT, $0-1
TEXT runtime·gogo(SB), NOSPLIT, $0-8
MOVD buf+0(FP), R0
MOVD gobuf_g(R0), g
MOVD gobuf_g(R0), R1
MOVD 0(R1), R2 // make sure g != nil
MOVD R1, g
MOVD gobuf_sp(R0), SP
// Put target PC at -8(SP), wasm_pc_f_loop will pick it up
@ -69,7 +71,6 @@ TEXT runtime·mcall(SB), NOSPLIT, $0-8
// save state in g->sched
MOVD 0(SP), g_sched+gobuf_pc(g) // caller's PC
MOVD $fn+0(FP), g_sched+gobuf_sp(g) // caller's SP
MOVD g, g_sched+gobuf_g(g)
// if g == g0 call badmcall
Get g
@ -143,7 +144,6 @@ TEXT runtime·systemstack(SB), NOSPLIT, $0-8
MOVD $runtime·systemstack_switch(SB), g_sched+gobuf_pc(g)
MOVD SP, g_sched+gobuf_sp(g)
MOVD g, g_sched+gobuf_g(g)
// switch to g0
MOVD R2, g
@ -270,7 +270,6 @@ TEXT runtime·morestack(SB), NOSPLIT, $0-0
// Set g->sched to context in f.
MOVD 0(SP), g_sched+gobuf_pc(g)
MOVD g, g_sched+gobuf_g(g)
MOVD $8(SP), g_sched+gobuf_sp(g) // f's SP
MOVD CTXT, g_sched+gobuf_ctxt(g)

24
src/runtime/proc.go
View File

@ -1281,6 +1281,9 @@ func mstart() {
mexit(osStack)
}
// The go:noinline is to guarantee the getcallerpc/getcallersp below are safe,
// so that we can set up g0.sched to return to the call of mstart1 above.
//go:noinline
func mstart1() {
_g_ := getg()
@ -1288,11 +1291,16 @@ func mstart1() {
throw("bad runtime·mstart")
}
// Record the caller for use as the top of stack in mcall and
// for terminating the thread.
// Set up m.g0.sched as a label returning returning to just
// after the mstart1 call in mstart0 above, for use by goexit0 and mcall.
// We're never coming back to mstart1 after we call schedule,
// so other calls can reuse the current frame.
save(getcallerpc(), getcallersp())
// And goexit0 does a gogo that needs to return from mstart1
// and let mstart0 exit the thread.
_g_.sched.g = guintptr(unsafe.Pointer(_g_))
_g_.sched.pc = getcallerpc()
_g_.sched.sp = getcallersp()
asminit()
minit()
@ -3445,11 +3453,19 @@ func goexit0(gp *g) {
func save(pc, sp uintptr) {
_g_ := getg()
if _g_ == _g_.m.g0 || _g_ == _g_.m.gsignal {
// m.g0.sched is special and must describe the context
// for exiting the thread. mstart1 writes to it directly.
// m.gsignal.sched should not be used at all.
// This check makes sure save calls do not accidentally
// run in contexts where they'd write to system g's.
throw("save on system g not allowed")
}
_g_.sched.pc = pc
_g_.sched.sp = sp
_g_.sched.lr = 0
_g_.sched.ret = 0
_g_.sched.g = guintptr(unsafe.Pointer(_g_))
// We need to ensure ctxt is zero, but can't have a write
// barrier here. However, it should always already be zero.
// Assert that.