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https://github.com/golang/go
synced 2024-09-05 07:54:46 +00:00
cmd/asm, cmd/compile, runtime: add -spectre=ret mode
This commit extends the -spectre flag to cmd/asm and adds a new Spectre mitigation mode "ret", which enables the use of retpolines. Retpolines prevent speculation about the target of an indirect jump or call and are described in more detail here: https://support.google.com/faqs/answer/7625886 Change-Id: I4f2cb982fa94e44d91e49bd98974fd125619c93a Reviewed-on: https://go-review.googlesource.com/c/go/+/222661 Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
parent
877ef86bec
commit
fc8a6336d1
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@ -24,6 +24,8 @@ var (
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AllErrors = flag.Bool("e", false, "no limit on number of errors reported")
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SymABIs = flag.Bool("gensymabis", false, "write symbol ABI information to output file, don't assemble")
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Newobj = flag.Bool("newobj", false, "use new object file format")
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Spectre = flag.String("spectre", "", "enable spectre mitigations in `list` (all, ret)")
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)
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var (
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@ -41,6 +41,19 @@ func main() {
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ctxt.Flag_dynlink = *flags.Dynlink
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ctxt.Flag_shared = *flags.Shared || *flags.Dynlink
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ctxt.Flag_newobj = *flags.Newobj
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switch *flags.Spectre {
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default:
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log.Printf("unknown setting -spectre=%s", *flags.Spectre)
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os.Exit(2)
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case "":
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// nothing
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case "index":
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// known to compiler; ignore here so people can use
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// the same list with -gcflags=-spectre=LIST and -asmflags=-spectrre=LIST
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case "all", "ret":
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ctxt.Retpoline = true
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}
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ctxt.Bso = bufio.NewWriter(os.Stdout)
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defer ctxt.Bso.Flush()
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@ -294,8 +294,11 @@ func Main(archInit func(*Arch)) {
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// nothing
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case "all":
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spectreIndex = true
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Ctxt.Retpoline = true
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case "index":
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spectreIndex = true
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case "ret":
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Ctxt.Retpoline = true
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}
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}
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@ -379,6 +379,11 @@ func checkSuffix(c *ctxt5, p *obj.Prog, o *Optab) {
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}
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func span5(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
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if ctxt.Retpoline {
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ctxt.Diag("-spectre=ret not supported on arm")
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ctxt.Retpoline = false // don't keep printing
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}
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var p *obj.Prog
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var op *obj.Prog
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@ -881,6 +881,11 @@ var prfopfield = []struct {
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}
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func span7(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
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if ctxt.Retpoline {
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ctxt.Diag("-spectre=ret not supported on arm64")
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ctxt.Retpoline = false // don't keep printing
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}
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p := cursym.Func.Text
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if p == nil || p.Link == nil { // handle external functions and ELF section symbols
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return
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@ -653,6 +653,7 @@ type Link struct {
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Flag_optimize bool
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Flag_locationlists bool
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Flag_newobj bool // use new object file format
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Retpoline bool // emit use of retpoline stubs for indirect jmp/call
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Bso *bufio.Writer
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Pathname string
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hashmu sync.Mutex // protects hash, funchash
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@ -402,6 +402,11 @@ var oprange [ALAST & obj.AMask][]Optab
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var xcmp [C_NCLASS][C_NCLASS]bool
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func span0(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
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if ctxt.Retpoline {
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ctxt.Diag("-spectre=ret not supported on mips")
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ctxt.Retpoline = false // don't keep printing
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}
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p := cursym.Func.Text
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if p == nil || p.Link == nil { // handle external functions and ELF section symbols
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return
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@ -1835,6 +1835,11 @@ func encodingForProg(p *obj.Prog) encoding {
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// assemble emits machine code.
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// It is called at the very end of the assembly process.
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func assemble(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
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if ctxt.Retpoline {
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ctxt.Diag("-spectre=ret not supported on riscv")
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ctxt.Retpoline = false // don't keep printing
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}
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var symcode []uint32
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for p := cursym.Func.Text; p != nil; p = p.Link {
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switch p.As {
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@ -442,6 +442,11 @@ var oprange [ALAST & obj.AMask][]Optab
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var xcmp [C_NCLASS][C_NCLASS]bool
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func spanz(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
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if ctxt.Retpoline {
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ctxt.Diag("-spectre=ret not supported on s390x")
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ctxt.Retpoline = false // don't keep printing
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}
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p := cursym.Func.Text
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if p == nil || p.Link == nil { // handle external functions and ELF section symbols
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return
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@ -1875,6 +1875,17 @@ func span6(ctxt *obj.Link, s *obj.LSym, newprog obj.ProgAlloc) {
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p.As = spadjop(ctxt, ASUBL, ASUBQ)
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}
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}
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if ctxt.Retpoline && (p.As == obj.ACALL || p.As == obj.AJMP) && (p.To.Type == obj.TYPE_REG || p.To.Type == obj.TYPE_MEM) {
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if p.To.Type != obj.TYPE_REG {
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ctxt.Diag("non-retpoline-compatible: %v", p)
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continue
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}
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p.To.Type = obj.TYPE_BRANCH
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p.To.Name = obj.NAME_EXTERN
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p.To.Sym = ctxt.Lookup("runtime.retpoline" + obj.Rconv(int(p.To.Reg)))
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p.To.Reg = 0
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p.To.Offset = 0
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}
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}
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var count int64 // rough count of number of instructions
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@ -510,7 +510,8 @@ TEXT NAME(SB), WRAPPER, $MAXSIZE-32; \
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/* call function */ \
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MOVQ f+8(FP), DX; \
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PCDATA $PCDATA_StackMapIndex, $0; \
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CALL (DX); \
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MOVQ (DX), AX; \
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CALL AX; \
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/* copy return values back */ \
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MOVQ argtype+0(FP), DX; \
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MOVQ argptr+16(FP), DI; \
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@ -1743,3 +1744,34 @@ TEXT runtime·panicSlice3CU(SB),NOSPLIT,$0-16
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DATA runtime·tls_g+0(SB)/8, $16
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GLOBL runtime·tls_g+0(SB), NOPTR, $8
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#endif
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// The compiler and assembler's -spectre=ret mode rewrites
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// all indirect CALL AX / JMP AX instructions to be
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// CALL retpolineAX / JMP retpolineAX.
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// See https://support.google.com/faqs/answer/7625886.
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#define RETPOLINE(reg) \
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/* CALL setup */ BYTE $0xE8; BYTE $(2+2); BYTE $0; BYTE $0; BYTE $0; \
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/* nospec: */ \
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/* PAUSE */ BYTE $0xF3; BYTE $0x90; \
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/* JMP nospec */ BYTE $0xEB; BYTE $-(2+2); \
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/* setup: */ \
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/* MOVQ AX, 0(SP) */ BYTE $0x48|((reg&8)>>1); BYTE $0x89; \
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BYTE $0x04|((reg&7)<<3); BYTE $0x24; \
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/* RET */ BYTE $0xC3
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TEXT runtime·retpolineAX(SB),NOSPLIT,$0; RETPOLINE(0)
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TEXT runtime·retpolineCX(SB),NOSPLIT,$0; RETPOLINE(1)
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TEXT runtime·retpolineDX(SB),NOSPLIT,$0; RETPOLINE(2)
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TEXT runtime·retpolineBX(SB),NOSPLIT,$0; RETPOLINE(3)
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/* SP is 4, can't happen / magic encodings */
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TEXT runtime·retpolineBP(SB),NOSPLIT,$0; RETPOLINE(5)
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TEXT runtime·retpolineSI(SB),NOSPLIT,$0; RETPOLINE(6)
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TEXT runtime·retpolineDI(SB),NOSPLIT,$0; RETPOLINE(7)
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TEXT runtime·retpolineR8(SB),NOSPLIT,$0; RETPOLINE(8)
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TEXT runtime·retpolineR9(SB),NOSPLIT,$0; RETPOLINE(9)
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TEXT runtime·retpolineR10(SB),NOSPLIT,$0; RETPOLINE(10)
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TEXT runtime·retpolineR11(SB),NOSPLIT,$0; RETPOLINE(11)
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TEXT runtime·retpolineR12(SB),NOSPLIT,$0; RETPOLINE(12)
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TEXT runtime·retpolineR13(SB),NOSPLIT,$0; RETPOLINE(13)
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TEXT runtime·retpolineR14(SB),NOSPLIT,$0; RETPOLINE(14)
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TEXT runtime·retpolineR15(SB),NOSPLIT,$0; RETPOLINE(15)
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@ -9,3 +9,20 @@ func stackcheck()
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// Called from assembly only; declared for go vet.
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func settls() // argument in DI
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// Retpolines, used by -spectre=ret flag in cmd/asm, cmd/compile.
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func retpolineAX()
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func retpolineCX()
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func retpolineDX()
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func retpolineBX()
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func retpolineBP()
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func retpolineSI()
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func retpolineDI()
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func retpolineR8()
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func retpolineR9()
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func retpolineR10()
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func retpolineR11()
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func retpolineR12()
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func retpolineR13()
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func retpolineR14()
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func retpolineR15()
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14
test/codegen/retpoline.go
Normal file
14
test/codegen/retpoline.go
Normal file
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@ -0,0 +1,14 @@
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// +build amd64
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// asmcheck -gcflags=-spectre=ret
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package codegen
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func CallFunc(f func()) {
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// amd64:`CALL\truntime.retpoline`
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f()
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}
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func CallInterface(x interface{ M() }) {
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// amd64:`CALL\truntime.retpoline`
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x.M()
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}
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