debug/gosym: add hook to disable recovers

debug/gosym assumes throughout that bogus input means a malformed file.
That's generally true, but not when you're changing the package.
In that case, the panic usually indicates a newly introduced bug,
and seeing the panic is really useful.

Add a manually-enabled way to make panics panic.

Change-Id: I07af6c7b982c4cf61180db29f07aa63576ba7837
Reviewed-on: https://go-review.googlesource.com/c/go/+/352949
Trust: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>

1 files changed, 23 insertions, 13 deletions

diff --git a/src/debug/gosym/pclntab.go b/src/debug/gosym/pclntab.go
index 555add67e3..5d65b7826a 100644
--- a/src/debug/gosym/pclntab.go
+++ b/src/debug/gosym/pclntab.go
@@ -193,10 +193,12 @@ func (t *LineTable) parsePclnTab() {
 	// Error paths through this code will default the version to 1.1.
 	t.version = ver11
 
-	defer func() {
-		// If we panic parsing, assume it's a Go 1.1 pclntab.
-		recover()
-	}()
+	if !disableRecover {
+		defer func() {
+			// If we panic parsing, assume it's a Go 1.1 pclntab.
+			recover()
+		}()
+	}
 
 	// Check header: 4-byte magic, two zeros, pc quantum, pointer size.
 	if len(t.Data) < 16 || t.Data[4] != 0 || t.Data[5] != 0 ||
@@ -265,9 +267,11 @@ func (t *LineTable) parsePclnTab() {
 // go12Funcs returns a slice of Funcs derived from the Go 1.2 pcln table.
 func (t *LineTable) go12Funcs() []Func {
 	// Assume it is malformed and return nil on error.
-	defer func() {
-		recover()
-	}()
+	if !disableRecover {
+		defer func() {
+			recover()
+		}()
+	}
 
 	n := len(t.functab) / int(t.ptrsize) / 2
 	funcs := make([]Func, n)
@@ -441,7 +445,7 @@ func (t *LineTable) findFileLine(entry uint64, filetab, linetab uint32, filenum,
 // go12PCToLine maps program counter to line number for the Go 1.2 pcln table.
 func (t *LineTable) go12PCToLine(pc uint64) (line int) {
 	defer func() {
-		if recover() != nil {
+		if !disableRecover && recover() != nil {
 			line = -1
 		}
 	}()
@@ -458,7 +462,7 @@ func (t *LineTable) go12PCToLine(pc uint64) (line int) {
 // go12PCToFile maps program counter to file name for the Go 1.2 pcln table.
 func (t *LineTable) go12PCToFile(pc uint64) (file string) {
 	defer func() {
-		if recover() != nil {
+		if !disableRecover && recover() != nil {
 			file = ""
 		}
 	}()
@@ -490,7 +494,7 @@ func (t *LineTable) go12PCToFile(pc uint64) (file string) {
 // go12LineToPC maps a (file, line) pair to a program counter for the Go 1.2/1.16 pcln table.
 func (t *LineTable) go12LineToPC(file string, line int) (pc uint64) {
 	defer func() {
-		if recover() != nil {
+		if !disableRecover && recover() != nil {
 			pc = 0
 		}
 	}()
@@ -552,12 +556,18 @@ func (t *LineTable) initFileMap() {
 // Every key maps to obj. That's not a very interesting map, but it provides
 // a way for callers to obtain the list of files in the program.
 func (t *LineTable) go12MapFiles(m map[string]*Obj, obj *Obj) {
-	defer func() {
-		recover()
-	}()
+	if !disableRecover {
+		defer func() {
+			recover()
+		}()
+	}
 
 	t.initFileMap()
 	for file := range t.fileMap {
 		m[file] = obj
 	}
 }
+
+// disableRecover causes this package not to swallow panics.
+// This is useful when making changes.
+const disableRecover = false