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[release-branch.go1.14] cmd/compile, runtime: mark R12 clobbered for write barrier call on PPC64 

When external linking, for large binaries, the external linker
may insert a trampoline for the write barrier call, which looks

0000000005a98cc8 <__long_branch_runtime.gcWriteBarrier>:
 5a98cc8:       86 01 82 3d     addis   r12,r2,390
 5a98ccc:       d8 bd 8c e9     ld      r12,-16936(r12)
 5a98cd0:       a6 03 89 7d     mtctr   r12
 5a98cd4:       20 04 80 4e     bctr

It clobbers R12 (and CTR, which is never live across a call).

As at compile time we don't know whether the binary is big and
what link mode will be used, I think we need to mark R12 as
clobbered for write barrier call. For extra safety (future-proof)
we mark caller-saved register that cannot be used for function
arguments, which includes R11, as potentially clobbered as well.

Updates #40851.
Fixes #40938.

Change-Id: Iedd901c5072f1127cc59b0a48cfeb4aaec81b519
Reviewed-on: https://go-review.googlesource.com/c/go/+/248917
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
(cherry picked from commit b58d297416)
Reviewed-on: https://go-review.googlesource.com/c/go/+/249697
This commit is contained in:
Cherry Zhang 2020-08-17 19:06:19 -04:00 committed by Dmitri Shuralyov
parent dd953ded33
commit 652aebf5fc
3 changed files with 24 additions and 23 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
src/cmd/compile/internal/ssa/gen/PPC64Ops.go
View File

@ -561,9 +561,9 @@ func init() {
{name: "LoweredAtomicOr8", argLength: 3, reg: gpstore, asm: "OR", faultOnNilArg0: true, hasSideEffects: true},
// LoweredWB invokes runtime.gcWriteBarrier. arg0=destptr, arg1=srcptr, arg2=mem, aux=runtime.gcWriteBarrier
// It preserves R0 through R15, g, and its arguments R20 and R21,
// It preserves R0 through R17 (except special registers R1, R2, R11, R12, R13), g, and its arguments R20 and R21,
// but may clobber anything else, including R31 (REGTMP).
{name: "LoweredWB", argLength: 3, reg: regInfo{inputs: []regMask{buildReg("R20"), buildReg("R21")}, clobbers: (callerSave &^ buildReg("R0 R3 R4 R5 R6 R7 R8 R9 R10 R11 R12 R14 R15 R20 R21 g")) | buildReg("R31")}, clobberFlags: true, aux: "Sym", symEffect: "None"},
{name: "LoweredWB", argLength: 3, reg: regInfo{inputs: []regMask{buildReg("R20"), buildReg("R21")}, clobbers: (callerSave &^ buildReg("R0 R3 R4 R5 R6 R7 R8 R9 R10 R14 R15 R16 R17 R20 R21 g")) | buildReg("R31")}, clobberFlags: true, aux: "Sym", symEffect: "None"},
// There are three of these functions so that they can have three different register inputs.
// When we check 0 <= c <= cap (A), then 0 <= b <= c (B), then 0 <= a <= b (C), we want the

2
src/cmd/compile/internal/ssa/opGen.go
View File

@ -24940,7 +24940,7 @@ var opcodeTable = [...]opInfo{
{0, 1048576}, // R20
{1, 2097152}, // R21
},
clobbers: 576460746931503104, // R16 R17 R18 R19 R22 R23 R24 R25 R26 R27 R28 R29 R31 F1 F2 F3 F4 F5 F6 F7 F8 F9 F10 F11 F12 F13 F14 F15 F16 F17 F18 F19 F20 F21 F22 F23 F24 F25 F26
clobbers: 576460746931312640, // R11 R12 R18 R19 R22 R23 R24 R25 R26 R27 R28 R29 R31 F1 F2 F3 F4 F5 F6 F7 F8 F9 F10 F11 F12 F13 F14 F15 F16 F17 F18 F19 F20 F21 F22 F23 F24 F25 F26
},
},
{

41
src/runtime/asm_ppc64x.s
View File

@ -916,23 +916,23 @@ TEXT ·checkASM(SB),NOSPLIT,$0-1
// - R20 is the destination of the write
// - R21 is the value being written at R20.
// It clobbers condition codes.
// It does not clobber R0 through R15,
// It does not clobber R0 through R17 (except special registers),
// but may clobber any other register, *including* R31.
TEXT runtime·gcWriteBarrier(SB),NOSPLIT,$112
// The standard prologue clobbers R31.
// We use R16 and R17 as scratch registers.
MOVD g_m(g), R16
MOVD m_p(R16), R16
MOVD (p_wbBuf+wbBuf_next)(R16), R17
// We use R18 and R19 as scratch registers.
MOVD g_m(g), R18
MOVD m_p(R18), R18
MOVD (p_wbBuf+wbBuf_next)(R18), R19
// Increment wbBuf.next position.
ADD $16, R17
MOVD R17, (p_wbBuf+wbBuf_next)(R16)
MOVD (p_wbBuf+wbBuf_end)(R16), R16
CMP R16, R17
ADD $16, R19
MOVD R19, (p_wbBuf+wbBuf_next)(R18)
MOVD (p_wbBuf+wbBuf_end)(R18), R18
CMP R18, R19
// Record the write.
MOVD R21, -16(R17) // Record value
MOVD (R20), R16 // TODO: This turns bad writes into bad reads.
MOVD R16, -8(R17) // Record *slot
MOVD R21, -16(R19) // Record value
MOVD (R20), R18 // TODO: This turns bad writes into bad reads.
MOVD R18, -8(R19) // Record *slot
// Is the buffer full? (flags set in CMP above)
BEQ flush
ret:
@ -956,11 +956,12 @@ flush:
MOVD R8, (FIXED_FRAME+56)(R1)
MOVD R9, (FIXED_FRAME+64)(R1)
MOVD R10, (FIXED_FRAME+72)(R1)
MOVD R11, (FIXED_FRAME+80)(R1)
MOVD R12, (FIXED_FRAME+88)(R1)
// R11, R12 may be clobbered by external-linker-inserted trampoline
// R13 is REGTLS
MOVD R14, (FIXED_FRAME+96)(R1)
MOVD R15, (FIXED_FRAME+104)(R1)
MOVD R14, (FIXED_FRAME+80)(R1)
MOVD R15, (FIXED_FRAME+88)(R1)
MOVD R16, (FIXED_FRAME+96)(R1)
MOVD R17, (FIXED_FRAME+104)(R1)
// This takes arguments R20 and R21.
CALL runtime·wbBufFlush(SB)
@ -975,10 +976,10 @@ flush:
MOVD (FIXED_FRAME+56)(R1), R8
MOVD (FIXED_FRAME+64)(R1), R9
MOVD (FIXED_FRAME+72)(R1), R10
MOVD (FIXED_FRAME+80)(R1), R11
MOVD (FIXED_FRAME+88)(R1), R12
MOVD (FIXED_FRAME+96)(R1), R14
MOVD (FIXED_FRAME+104)(R1), R15
MOVD (FIXED_FRAME+80)(R1), R14
MOVD (FIXED_FRAME+88)(R1), R15
MOVD (FIXED_FRAME+96)(R1), R16
MOVD (FIXED_FRAME+104)(R1), R17
JMP ret
// Note: these functions use a special calling convention to save generated code space.