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feat(asm): emit the amd64 stack-split guard and morestack block

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petrbalvin
2026-09-14 20:35:55 +02:00
parent 89fa6ea15e
commit 1d8e68c574
5 changed files with 500 additions and 23 deletions
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asm/goobj.go
+85 -13
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@@ -94,10 +94,12 @@ const (
)
// Relocation types (cmd/internal/objabi).
// R_PCREL and R_ADDR are stable across Go versions.
// R_ADDR, R_CALL, R_PCREL and R_TLS_LE are stable across Go versions.
const (
relocPCRel = 14 // R_PCREL
relocAddr = 1 // R_ADDR
relocCall = 7 // R_CALL
relocPCRel = 14 // R_PCREL
relocTLSLE = 15 // R_TLS_LE
)
// relocDWTXTADDRU4 returns the R_DWTXTADDR_U4 relocation type for the
@@ -140,10 +142,20 @@ func isGo127OrLater() bool {
// Special package indices for symbol references.
const (
pkgIdxNone = 0x7fffffff
pkgIdxSelf = 0x7ffffffb
pkgIdxNone = 0x7fffffff
pkgIdxSelf = 0x7ffffffb
pkgIdxBuiltin = 0x7ffffffc
)
// goobjBuiltinMorestackNoctxt is the index of runtime.morestack_noctxt in
// cmd/internal/goobj/builtinlist.go of the toolchain the object targets
// (246 since Go 1.25; the list is append-only).
const goobjBuiltinMorestackNoctxt = 246
// goobjBuiltinMorestack is the builtin reference the toolchain emits for the
// stack-guard call.
var goobjBuiltinMorestack = "runtime\u00b7morestack_noctxt"
const goobjMagic = "\x00go120ld"
// goSym is one symbol definition under construction.
@@ -184,8 +196,18 @@ func (img *Image) GOObject(pkgPath, srcPath string) ([]byte, error) {
if err != nil {
return nil, err
}
// amd64: MinLC 1, R_PCREL for the code relocations.
return img.emitGOObject(pkgPath, srcPath, pre, 1, func(Reloc) (uint16, uint8) { return relocPCRel, 4 })
// amd64: MinLC 1, R_PCREL for displacements, R_CALL for calls and
// R_TLS_LE for the stack-guard TLS load.
return img.emitGOObject(pkgPath, srcPath, pre, 1, func(r Reloc) (uint16, uint8) {
switch r.Kind {
case RelCall:
return relocCall, 4
case RelTLSLE:
return relocTLSLE, 4
default:
return relocPCRel, 4
}
})
}
// emitGOObject assembles the GOOBJ payload for any architecture. pre is
@@ -247,7 +269,7 @@ func (img *Image) emitGOObject(pkgPath, srcPath string, pre []byte, minLC int, r
// their relocations cover whole AUIPC/pcalau12i pairs, so
// zeroing r.Off would erase the opcode/register bits the linker
// preserves when it patches only the immediate.
if r.Kind != RelPCRel32 {
if r.Kind != RelPCRel32 && r.Kind != RelCall {
continue
}
if r.Off >= 0 && r.Off+4 <= len(code) {
@@ -320,6 +342,13 @@ func (img *Image) emitGOObject(pkgPath, srcPath string, pre []byte, minLC int, r
)
}
// Index the non-package TEXT definitions by short name for the internal
// call references.
textNpIdx := map[string]int{}
for i, fn := range img.Funcs {
textNpIdx[fn.Name] = fnNpIdx[i]
}
// Resolve external symbol references (cross-package). Build the
// package index table and determine each external symbol's SymIdx
// by reading the target package's export data.
@@ -327,10 +356,20 @@ func (img *Image) emitGOObject(pkgPath, srcPath string, pre []byte, minLC int, r
var extPkgIdx map[string]int
var extSymIdx map[string]int
if len(img.Externals) > 0 {
var err error
extPkgTable, extPkgIdx, extSymIdx, err = resolveExternalSymbols(img.Externals)
if err != nil {
return nil, fmt.Errorf("GOOBJ emission: resolving external symbols: %w", err)
// The morestack call is a builtin reference, not a resolved external.
var need []string
for _, n := range img.Externals {
if n == goobjBuiltinMorestack {
continue
}
need = append(need, n)
}
if len(need) > 0 {
var err error
extPkgTable, extPkgIdx, extSymIdx, err = resolveExternalSymbols(need)
if err != nil {
return nil, fmt.Errorf("GOOBJ emission: resolving external symbols: %w", err)
}
}
}
@@ -342,6 +381,31 @@ func (img *Image) emitGOObject(pkgPath, srcPath string, pre []byte, minLC int, r
si := len(defs) + fnNpIdx[i]
for _, r := range fn.Relocs {
typ, size := relocField(r)
if r.Kind == RelTLSLE {
// The TLS load has no symbol: {0, 0} is the nil ref.
var rec [23]byte
binary.LittleEndian.PutUint32(rec[0:], uint32(int32(r.Off)))
rec[4] = size
binary.LittleEndian.PutUint16(rec[5:], typ)
binary.LittleEndian.PutUint64(rec[7:], uint64(r.Addend))
binary.LittleEndian.PutUint32(rec[15:], 0)
binary.LittleEndian.PutUint32(rec[19:], 0)
symRelocs[si] = append(symRelocs[si], rec[:]...)
continue
}
if r.External && r.Kind == RelCall && r.Name == goobjBuiltinMorestack {
// The stack-guard morestack call uses the toolchain's
// builtin reference.
var rec [23]byte
binary.LittleEndian.PutUint32(rec[0:], uint32(int32(r.Off)))
rec[4] = size
binary.LittleEndian.PutUint16(rec[5:], typ)
binary.LittleEndian.PutUint64(rec[7:], uint64(r.Addend))
binary.LittleEndian.PutUint32(rec[15:], pkgIdxBuiltin)
binary.LittleEndian.PutUint32(rec[19:], goobjBuiltinMorestackNoctxt)
symRelocs[si] = append(symRelocs[si], rec[:]...)
continue
}
if r.External {
// Split package-qualified name: "runtime·morestack" → runtime, morestack.
pkg, name := splitQualified(r.Name)
@@ -366,16 +430,24 @@ func (img *Image) emitGOObject(pkgPath, srcPath string, pre []byte, minLC int, r
symRelocs[si] = append(symRelocs[si], rec[:]...)
continue
}
pkg := uint32(pkgIdxSelf)
di, ok := defIdx[r.Name]
if !ok {
return nil, fmt.Errorf("GOOBJ emission: reference to unknown symbol %q", r.Name)
// A call to a TEXT function of the same file references the
// non-package definition table.
ni, isText := textNpIdx[r.Name]
if !isText || r.Kind != RelCall {
return nil, fmt.Errorf("GOOBJ emission: reference to unknown symbol %q", r.Name)
}
pkg = pkgIdxNone
di = ni
}
var rec [23]byte
binary.LittleEndian.PutUint32(rec[0:], uint32(int32(r.Off)))
rec[4] = size // field width
binary.LittleEndian.PutUint16(rec[5:], typ)
binary.LittleEndian.PutUint64(rec[7:], uint64(r.Addend))
binary.LittleEndian.PutUint32(rec[15:], pkgIdxSelf)
binary.LittleEndian.PutUint32(rec[15:], pkg)
binary.LittleEndian.PutUint32(rec[19:], uint32(di))
symRelocs[si] = append(symRelocs[si], rec[:]...)
}