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. Fixes #40851. Change-Id: Iedd901c5072f1127cc59b0a48cfeb4aaec81b519 Reviewed-on: https://go-review.googlesource.com/c/go/+/248917 Run-TryBot: Cherry Zhang <[email protected]> TryBot-Result: Gobot Gobot <[email protected]> Reviewed-by: Austin Clements <[email protected]>
cloudflare · Aug 18, 2020 · b58d297 · b58d297
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diff --git a/src/cmd/compile/internal/ssa/gen/PPC64Ops.go b/src/cmd/compile/internal/ssa/gen/PPC64Ops.go
@@ -645,9 +645,9 @@ 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

diff --git a/src/cmd/compile/internal/ssa/opGen.go b/src/cmd/compile/internal/ssa/opGen.go
diff --git a/src/runtime/asm_ppc64x.s b/src/runtime/asm_ppc64x.s
@@ -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.