1 files changed, 115 insertions, 0 deletions
diff --git a/src/runtime/symtabinl.go b/src/runtime/symtabinl.go
new file mode 100644
index 0000000..9273b49
--- /dev/null
+++ b/src/runtime/symtabinl.go
@@ -0,0 +1,115 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package runtime
+
+import "internal/abi"
+
+// inlinedCall is the encoding of entries in the FUNCDATA_InlTree table.
+type inlinedCall struct {
+	funcID    abi.FuncID // type of the called function
+	_         [3]byte
+	nameOff   int32 // offset into pclntab for name of called function
+	parentPc  int32 // position of an instruction whose source position is the call site (offset from entry)
+	startLine int32 // line number of start of function (func keyword/TEXT directive)
+}
+
+// An inlineUnwinder iterates over the stack of inlined calls at a PC by
+// decoding the inline table. The last step of iteration is always the frame of
+// the physical function, so there's always at least one frame.
+//
+// This is typically used as:
+//
+//	for u, uf := newInlineUnwinder(...); uf.valid(); uf = u.next(uf) { ... }
+//
+// Implementation note: This is used in contexts that disallow write barriers.
+// Hence, the constructor returns this by value and pointer receiver methods
+// must not mutate pointer fields. Also, we keep the mutable state in a separate
+// struct mostly to keep both structs SSA-able, which generates much better
+// code.
+type inlineUnwinder struct {
+	f       funcInfo
+	inlTree *[1 << 20]inlinedCall
+}
+
+// An inlineFrame is a position in an inlineUnwinder.
+type inlineFrame struct {
+	// pc is the PC giving the file/line metadata of the current frame. This is
+	// always a "call PC" (not a "return PC"). This is 0 when the iterator is
+	// exhausted.
+	pc uintptr
+
+	// index is the index of the current record in inlTree, or -1 if we are in
+	// the outermost function.
+	index int32
+}
+
+// newInlineUnwinder creates an inlineUnwinder initially set to the inner-most
+// inlined frame at PC. PC should be a "call PC" (not a "return PC").
+//
+// This unwinder uses non-strict handling of PC because it's assumed this is
+// only ever used for symbolic debugging. If things go really wrong, it'll just
+// fall back to the outermost frame.
+func newInlineUnwinder(f funcInfo, pc uintptr) (inlineUnwinder, inlineFrame) {
+	inldata := funcdata(f, abi.FUNCDATA_InlTree)
+	if inldata == nil {
+		return inlineUnwinder{f: f}, inlineFrame{pc: pc, index: -1}
+	}
+	inlTree := (*[1 << 20]inlinedCall)(inldata)
+	u := inlineUnwinder{f: f, inlTree: inlTree}
+	return u, u.resolveInternal(pc)
+}
+
+func (u *inlineUnwinder) resolveInternal(pc uintptr) inlineFrame {
+	return inlineFrame{
+		pc: pc,
+		// Conveniently, this returns -1 if there's an error, which is the same
+		// value we use for the outermost frame.
+		index: pcdatavalue1(u.f, abi.PCDATA_InlTreeIndex, pc, false),
+	}
+}
+
+func (uf inlineFrame) valid() bool {
+	return uf.pc != 0
+}
+
+// next returns the frame representing uf's logical caller.
+func (u *inlineUnwinder) next(uf inlineFrame) inlineFrame {
+	if uf.index < 0 {
+		uf.pc = 0
+		return uf
+	}
+	parentPc := u.inlTree[uf.index].parentPc
+	return u.resolveInternal(u.f.entry() + uintptr(parentPc))
+}
+
+// isInlined returns whether uf is an inlined frame.
+func (u *inlineUnwinder) isInlined(uf inlineFrame) bool {
+	return uf.index >= 0
+}
+
+// srcFunc returns the srcFunc representing the given frame.
+func (u *inlineUnwinder) srcFunc(uf inlineFrame) srcFunc {
+	if uf.index < 0 {
+		return u.f.srcFunc()
+	}
+	t := &u.inlTree[uf.index]
+	return srcFunc{
+		u.f.datap,
+		t.nameOff,
+		t.startLine,
+		t.funcID,
+	}
+}
+
+// fileLine returns the file name and line number of the call within the given
+// frame. As a convenience, for the innermost frame, it returns the file and
+// line of the PC this unwinder was started at (often this is a call to another
+// physical function).
+//
+// It returns "?", 0 if something goes wrong.
+func (u *inlineUnwinder) fileLine(uf inlineFrame) (file string, line int) {
+	file, line32 := funcline1(u.f, uf.pc, false)
+	return file, int(line32)
+}