runtime: add Go symtab implementation

LGTM=khr
R=khr, dvyukov, dave
CC=golang-codereviews, rsc
https://golang.org/cl/124300044

src/pkg/runtime/extern.go

@@ -97,37 +97,6 @@ func Caller(skip int) (pc uintptr, file string, line int, ok bool)
 // It returns the number of entries written to pc.
 func Callers(skip int, pc []uintptr) int
 
-type Func struct {
-	opaque struct{} // unexported field to disallow conversions
-}
-
-// FuncForPC returns a *Func describing the function that contains the
-// given program counter address, or else nil.
-func FuncForPC(pc uintptr) *Func
-
-// Name returns the name of the function.
-func (f *Func) Name() string {
-	return funcname_go(f)
-}
-
-// Entry returns the entry address of the function.
-func (f *Func) Entry() uintptr {
-	return funcentry_go(f)
-}
-
-// FileLine returns the file name and line number of the
-// source code corresponding to the program counter pc.
-// The result will not be accurate if pc is not a program
-// counter within f.
-func (f *Func) FileLine(pc uintptr) (file string, line int) {
-	return funcline_go(f, pc)
-}
-
-// implemented in symtab.c
-func funcline_go(*Func, uintptr) (string, int)
-func funcname_go(*Func) string
-func funcentry_go(*Func) uintptr
-
 func getgoroot() string
 
 // GOROOT returns the root of the Go tree.

src/pkg/runtime/runtime.h

@@ -447,7 +447,7 @@ enum
 // Layout of in-memory per-function information prepared by linker
 // See http://golang.org/s/go12symtab.
 // Keep in sync with linker and with ../../libmach/sym.c
-// and with package debug/gosym.
+// and with package debug/gosym and with symtab.go in package runtime.
 struct	Func
 {
 	uintptr	entry;	// start pc

src/pkg/runtime/symtab.c

@@ -5,7 +5,6 @@
 // Runtime symbol table parsing.
 // See http://golang.org/s/go12symtab for an overview.
 
-package runtime
 #include "runtime.h"
 #include "defs_GOOS_GOARCH.h"
 #include "os_GOOS.h"
@@ -23,9 +22,14 @@ struct Ftab
 extern byte pclntab[];
 
 static Ftab *ftab;
-static uintptr nftab;
+extern uintptr runtime·nftab;
 static uint32 *filetab;
-static uint32 nfiletab;
+extern uint32 runtime·nfiletab;
+
+extern uintptr runtime·pclntab;
+extern uintptr runtime·ftab0;
+extern uintptr runtime·filetab0;
+extern uint32 runtime·pcquantum;
 
 static String end = { (uint8*)"end", 3 };
 
@@ -43,22 +47,27 @@ runtime·symtabinit(void)
 		runtime·throw("invalid function symbol table\n");
 	}
 
-	nftab = *(uintptr*)(pclntab+8);
+	runtime·nftab = *(uintptr*)(pclntab+8);
 	ftab = (Ftab*)(pclntab+8+sizeof(void*));
-	for(i=0; i<nftab; i++) {
-		// NOTE: ftab[nftab].entry is legal; it is the address beyond the final function.
+	for(i=0; i<runtime·nftab; i++) {
+		// NOTE: ftab[runtime·nftab].entry is legal; it is the address beyond the final function.
 		if(ftab[i].entry > ftab[i+1].entry) {
 			f1 = (Func*)(pclntab + ftab[i].funcoff);
 			f2 = (Func*)(pclntab + ftab[i+1].funcoff);
-			runtime·printf("function symbol table not sorted by program counter: %p %s > %p %s", ftab[i].entry, runtime·funcname(f1), ftab[i+1].entry, i+1 == nftab ? "end" : runtime·funcname(f2));
+			runtime·printf("function symbol table not sorted by program counter: %p %s > %p %s", ftab[i].entry, runtime·funcname(f1), ftab[i+1].entry, i+1 == runtime·nftab ? "end" : runtime·funcname(f2));
 			for(j=0; j<=i; j++)
 				runtime·printf("\t%p %s\n", ftab[j].entry, runtime·funcname((Func*)(pclntab + ftab[j].funcoff)));
 			runtime·throw("invalid runtime symbol table");
 		}
 	}
 	
-	filetab = (uint32*)(pclntab + *(uint32*)&ftab[nftab].funcoff);
-	nfiletab = filetab[0];
+	filetab = (uint32*)(pclntab + *(uint32*)&ftab[runtime·nftab].funcoff);
+	runtime·nfiletab = filetab[0];
+
+	runtime·pcquantum = PCQuantum;
+	runtime·pclntab = (uintptr)pclntab;
+	runtime·ftab0 = (uintptr)ftab;
+	runtime·filetab0 = (uintptr)filetab;
 }
 
 static uint32
@@ -187,7 +196,7 @@ funcline(Func *f, uintptr targetpc, String *file, bool strict)
 	*file = unknown;
 	fileno = pcvalue(f, f->pcfile, targetpc, strict);
 	line = pcvalue(f, f->pcln, targetpc, strict);
-	if(fileno == -1 || line == -1 || fileno >= nfiletab) {
+	if(fileno == -1 || line == -1 || fileno >= runtime·nfiletab) {
 		// runtime·printf("looking for %p in %S got file=%d line=%d\n", targetpc, *f->name, fileno, line);
 		return 0;
 	}
@@ -228,34 +237,20 @@ runtime·funcarglen(Func *f, uintptr targetpc)
 	return runtime·pcdatavalue(f, PCDATA_ArgSize, targetpc-PCQuantum);
 }
 
-func funcline_go(f *Func, targetpc uintptr) (retfile String, retline int) {
-	// Pass strict=false here, because anyone can call this function,
-	// and they might just be wrong about targetpc belonging to f.
-	retline = funcline(f, targetpc, &retfile, false);
-}
-
-func funcname_go(f *Func) (ret String) {
-	ret = runtime·gostringnocopy((uint8*)runtime·funcname(f));
-}
-
-func funcentry_go(f *Func) (ret uintptr) {
-	ret = f->entry;
-}
-
 Func*
 runtime·findfunc(uintptr addr)
 {
 	Ftab *f;
 	int32 nf, n;
 
-	if(nftab == 0)
+	if(runtime·nftab == 0)
 		return nil;
-	if(addr < ftab[0].entry || addr >= ftab[nftab].entry)
+	if(addr < ftab[0].entry || addr >= ftab[runtime·nftab].entry)
 		return nil;
 
 	// binary search to find func with entry <= addr.
 	f = ftab;
-	nf = nftab;
+	nf = runtime·nftab;
 	while(nf > 0) {
 		n = nf/2;
 		if(f[n].entry <= addr && addr < f[n+1].entry)
@@ -276,10 +271,6 @@ runtime·findfunc(uintptr addr)
 	return nil;
 }
 
-func FuncForPC(pc uintptr) (ret *Func) {
-	ret = runtime·findfunc(pc);
-}
-
 static bool
 hasprefix(String s, int8 *p)
 {

src/pkg/runtime/symtab.go

@@ -0,0 +1,153 @@
+// Copyright 2014 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 "unsafe"
+
+// FuncForPC returns a *Func describing the function that contains the
+// given program counter address, or else nil.
+func FuncForPC(pc uintptr) *Func {
+	if nftab == 0 {
+		return nil
+	}
+
+	if pc < ftabi(0).entry || pc >= ftabi(nftab).entry {
+		return nil
+	}
+
+	// binary search to find func with entry <= pc.
+	lo := uintptr(0)
+	nf := nftab
+	for nf > 0 {
+		n := nf / 2
+		f := ftabi(lo + n)
+		if f.entry <= pc && pc < ftabi(lo+n+1).entry {
+			return (*Func)(unsafe.Pointer(pclntab + f.funcoff))
+		} else if pc < f.entry {
+			nf = n
+		} else {
+			lo += n + 1
+			nf -= n + 1
+		}
+	}
+
+	gothrow("FuncForPC: binary search failed")
+	return nil
+}
+
+// Name returns the name of the function.
+func (f *Func) Name() string {
+	return cstringToGo(pclntab + uintptr(f.nameoff))
+}
+
+// Entry returns the entry address of the function.
+func (f *Func) Entry() uintptr {
+	return f.entry
+}
+
+// FileLine returns the file name and line number of the
+// source code corresponding to the program counter pc.
+// The result will not be accurate if pc is not a program
+// counter within f.
+func (f *Func) FileLine(pc uintptr) (file string, line int) {
+	fileno := f.pcvalue(f.pcfile, pc)
+	if fileno == -1 || fileno >= int32(nfiletab) {
+		return "?", 0
+	}
+	line = int(f.pcvalue(f.pcln, pc))
+	if line == -1 {
+		return "?", 0
+	}
+	file = cstringToGo(pclntab + uintptr(filetabi(uintptr(fileno))))
+	return file, line
+}
+
+// Return associated data value for targetpc in func f.
+func (f *Func) pcvalue(off int32, targetpc uintptr) int32 {
+	if off == 0 {
+		return -1
+	}
+	p := pclntab + uintptr(off)
+	pc := f.entry
+	val := int32(-1)
+	for step(&p, &pc, &val, pc == f.entry) {
+		if targetpc < pc {
+			return val
+		}
+	}
+	return -1
+}
+
+// step advances to the next pc, value pair in the encoded table.
+func step(p *uintptr, pc *uintptr, val *int32, first bool) bool {
+	uvdelta := readvarint(p)
+	if uvdelta == 0 && !first {
+		return false
+	}
+	if uvdelta&1 != 0 {
+		uvdelta = ^(uvdelta >> 1)
+	} else {
+		uvdelta >>= 1
+	}
+	vdelta := int32(uvdelta)
+	pcdelta := readvarint(p) * pcquantum
+	*pc += uintptr(pcdelta)
+	*val += vdelta
+	return true
+}
+
+// readvarint reads a varint from *p and advances *p.
+func readvarint(pp *uintptr) uint32 {
+	var v, shift uint32
+	p := *pp
+	for {
+		b := *(*byte)(unsafe.Pointer(p))
+		p++
+		v |= (uint32(b) & 0x7F) << shift
+		if b&0x80 == 0 {
+			break
+		}
+		shift += 7
+	}
+	*pp = p
+	return v
+}
+
+// Populated by runtime·symtabinit during bootstrapping. Treat as immutable.
+var (
+	pclntab   uintptr // address of pclntab
+	ftab0     uintptr // address of first ftab entry
+	nftab     uintptr
+	filetab0  uintptr // address of first filetab entry
+	nfiletab  uint32
+	pcquantum uint32
+)
+
+type Func struct {
+	entry   uintptr // start pc
+	nameoff int32   // function name
+
+	args  int32 // in/out args size
+	frame int32 // legacy frame size; use pcsp if possible
+
+	pcsp      int32
+	pcfile    int32
+	pcln      int32
+	npcdata   int32
+	nfuncdata int32
+}
+
+type ftab struct {
+	entry   uintptr
+	funcoff uintptr
+}
+
+func ftabi(i uintptr) (f ftab) {
+	return *(*ftab)(unsafe.Pointer(ftab0 + i*unsafe.Sizeof(f)))
+}
+
+func filetabi(i uintptr) (f uint32) {
+	return *(*uint32)(unsafe.Pointer(filetab0 + i*unsafe.Sizeof(f)))
+}