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https://github.com/golang/go
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runtime: save g to TLS more aggressively
This is one of those "how did this ever work?" bugs. The current build failures are happening because a fault comes up while executing on m->curg on a system-created thread using an m obtained from needm, but TLS is set to m->g0, not m->curg. On fault, sigtramp starts executing, assumes r10 (g) might be incorrect, reloads it from TLS, and gets m->g0, not m->curg. Then sighandler dutifully pushes a call to sigpanic onto the stack and returns to it. We're now executing on the m->curg stack but with g=m->g0. Sigpanic does a stack split check, sees that the SP is not in range (50% chance depending on relative ordering of m->g0's and m->curg's stacks), and then calls morestack. Morestack sees that g=m->g0 and crashes the program. The fix is to replace every change of g in asm_arm.s with a call to a function that both updates g and saves the updated g to TLS. Why did it start happening? That's unclear. Unfortunately there were other bugs in the initial checkin that mask exactly which of a sequence of CLs started the behavior where sigpanic would end up tripping the stack split. Fixes arm build. Fixes #8675. LGTM=iant R=golang-codereviews, iant CC=dave, golang-codereviews, khr, minux, r https://golang.org/cl/135570043
This commit is contained in:
Russ Cox
parent
2c14dbe458
commit
b4bfa6c964
@ -6,7 +6,7 @@ enum {
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thechar = '5',
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BigEndian = 0,
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CacheLineSize = 32,
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RuntimeGogoBytes = 84,
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RuntimeGogoBytes = 60,
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#ifdef GOOS_nacl
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PhysPageSize = 65536,
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#else
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@ -129,11 +129,19 @@ TEXT runtime·gosave(SB),NOSPLIT,$-4-4
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// restore state from Gobuf; longjmp
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TEXT runtime·gogo(SB),NOSPLIT,$-4-4
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MOVW 0(FP), R1 // gobuf
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MOVW gobuf_g(R1), g
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MOVW 0(g), R2 // make sure g != nil
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MOVB runtime·iscgo(SB), R2
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CMP $0, R2 // if in Cgo, we have to save g
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BL.NE runtime·save_g(SB) // this call will clobber R0
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MOVW gobuf_g(R1), R0
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BL setg<>(SB)
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// NOTE: We updated g above, and we are about to update SP.
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// Until LR and PC are also updated, the g/SP/LR/PC quadruple
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// are out of sync and must not be used as the basis of a traceback.
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// Sigprof skips the traceback when SP is not within g's bounds,
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// and when the PC is inside this function, runtime.gogo.
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// Since we are about to update SP, until we complete runtime.gogo
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// we must not leave this function. In particular, no calls
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// after this point: it must be straight-line code until the
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// final B instruction.
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// See large comment in sigprof for more details.
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MOVW gobuf_sp(R1), SP // restore SP
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MOVW gobuf_lr(R1), LR
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MOVW gobuf_ret(R1), R0
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@ -143,8 +151,8 @@ TEXT runtime·gogo(SB),NOSPLIT,$-4-4
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MOVW R11, gobuf_ret(R1)
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MOVW R11, gobuf_lr(R1)
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MOVW R11, gobuf_ctxt(R1)
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CMP R11, R11 // set condition codes for == test, needed by stack split
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MOVW gobuf_pc(R1), R11
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CMP R11, R11 // set condition codes for == test, needed by stack split
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B (R11)
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// func mcall(fn func(*g))
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@ -162,7 +170,8 @@ TEXT runtime·mcall(SB),NOSPLIT,$-4-4
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// Switch to m->g0 & its stack, call fn.
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MOVW g, R1
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MOVW g_m(g), R8
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MOVW m_g0(R8), g
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MOVW m_g0(R8), R0
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BL setg<>(SB)
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CMP g, R1
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B.NE 2(PC)
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B runtime·badmcall(SB)
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@ -218,7 +227,10 @@ oncurg:
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MOVW g, (g_sched+gobuf_g)(g)
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// switch to g0
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MOVW R2, g
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MOVW R0, R5
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MOVW R2, R0
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BL setg<>(SB)
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MOVW R5, R0
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MOVW (g_sched+gobuf_sp)(R2), R3
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// make it look like mstart called onM on g0, to stop traceback
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SUB $4, R3, R3
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@ -234,7 +246,8 @@ oncurg:
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// switch back to g
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MOVW g_m(g), R1
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MOVW m_curg(R1), g
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MOVW m_curg(R1), R0
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BL setg<>(SB)
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MOVW (g_sched+gobuf_sp)(g), SP
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MOVW $0, R3
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MOVW R3, (g_sched+gobuf_sp)(g)
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@ -293,7 +306,8 @@ TEXT runtime·morestack(SB),NOSPLIT,$-4-0
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MOVW g, (m_morebuf+gobuf_g)(R8)
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// Call newstack on m->g0's stack.
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MOVW m_g0(R8), g
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MOVW m_g0(R8), R0
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BL setg<>(SB)
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MOVW (g_sched+gobuf_sp)(g), SP
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BL runtime·newstack(SB)
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@ -433,7 +447,8 @@ TEXT runtime·lessstack(SB),NOSPLIT,$-4-0
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MOVW R0, m_cret(R8)
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// Call oldstack on m->g0's stack.
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MOVW m_g0(R8), g
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MOVW m_g0(R8), R0
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BL setg<>(SB)
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MOVW (g_sched+gobuf_sp)(g), SP
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BL runtime·oldstack(SB)
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@ -485,7 +500,7 @@ TEXT runtime·asmcgocall_errno(SB),NOSPLIT,$0-12
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TEXT asmcgocall<>(SB),NOSPLIT,$0-0
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// fn in R1, arg in R0.
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MOVW R13, R2
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MOVW g, R5
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MOVW g, R4
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// Figure out if we need to switch to m->g0 stack.
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// We get called to create new OS threads too, and those
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@ -493,21 +508,27 @@ TEXT asmcgocall<>(SB),NOSPLIT,$0-0
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MOVW g_m(g), R8
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MOVW m_g0(R8), R3
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CMP R3, g
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BEQ 4(PC)
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BEQ asmcgocall_g0
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BL gosave<>(SB)
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MOVW R3, g
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MOVW R0, R5
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MOVW R3, R0
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BL setg<>(SB)
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MOVW R5, R0
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MOVW (g_sched+gobuf_sp)(g), R13
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// Now on a scheduling stack (a pthread-created stack).
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asmcgocall_g0:
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SUB $24, R13
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BIC $0x7, R13 // alignment for gcc ABI
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MOVW R5, 20(R13) // save old g
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MOVW R4, 20(R13) // save old g
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MOVW R2, 16(R13) // save old SP
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// R0 already contains the first argument
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BL (R1)
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// Restore registers, g, stack pointer.
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MOVW 20(R13), g
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MOVW R0, R5
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MOVW 20(R13), R0
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BL setg<>(SB)
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MOVW R5, R0
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MOVW 16(R13), R13
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RET
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@ -572,7 +593,8 @@ havem:
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// the earlier calls.
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//
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// In the new goroutine, -8(SP) and -4(SP) are unused.
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MOVW m_curg(R8), g
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MOVW m_curg(R8), R0
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BL setg<>(SB)
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MOVW (g_sched+gobuf_sp)(g), R4 // prepare stack as R4
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MOVW (g_sched+gobuf_pc)(g), R5
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MOVW R5, -12(R4)
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@ -589,7 +611,8 @@ havem:
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// (Unlike m->curg, the g0 goroutine never uses sched.pc,
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// so we do not have to restore it.)
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MOVW g_m(g), R8
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MOVW m_g0(R8), g
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MOVW m_g0(R8), R0
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BL setg<>(SB)
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MOVW (g_sched+gobuf_sp)(g), R13
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MOVW savedsp-8(SP), R4
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MOVW R4, (g_sched+gobuf_sp)(g)
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@ -606,14 +629,20 @@ havem:
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RET
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// void setg(G*); set g. for use by needm.
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TEXT runtime·setg(SB),NOSPLIT,$0-4
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MOVW gg+0(FP), g
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TEXT runtime·setg(SB),NOSPLIT,$-4-4
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MOVW gg+0(FP), R0
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B setg<>(SB)
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TEXT setg<>(SB),NOSPLIT,$-4-0
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MOVW R0, g
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// Save g to thread-local storage.
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MOVB runtime·iscgo(SB), R0
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CMP $0, R0
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BL.NE runtime·save_g(SB)
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B.EQ 2(PC)
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B runtime·save_g(SB)
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MOVW g, R0
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RET
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TEXT runtime·getcallerpc(SB),NOSPLIT,$-4-4
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@ -22,9 +22,11 @@
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// ARM code that will overwrite those registers.
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// NOTE: runtime.gogo assumes that R1 is preserved by this function.
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// runtime.mcall assumes this function only clobbers R0 and R11.
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TEXT runtime·save_g(SB),NOSPLIT,$0
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// Returns with g in R0.
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TEXT runtime·save_g(SB),NOSPLIT,$-4
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#ifdef GOOS_nacl
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// nothing to do as nacl/arm does not use TLS at all.
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MOVW g, R0 // preserve R0 across call to setg<>
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RET
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#endif
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MRC 15, 0, R0, C13, C0, 3 // fetch TLS base pointer
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@ -38,6 +40,7 @@ TEXT runtime·save_g(SB),NOSPLIT,$0
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#endif
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ADD R11, R0
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MOVW g, 0(R0)
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MOVW g, R0 // preserve R0 across call to setg<>
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RET
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// load_g loads the g register from pthread-provided
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