[dev.link] cmd/link: stop renumbering files for pclntab generation

Creates two new symbols: runtime.cutab, and runtime.filetab, and strips
the filenames out of runtime.pclntab_old.

All stats are for cmd/compile.

Time:
Pclntab_GC                   48.2ms ± 3%    45.5ms ± 9%     -5.47%  (p=0.004 n=9+9)

Alloc/op:
Pclntab_GC                   30.0MB ± 0%    29.5MB ± 0%     -1.88%  (p=0.000 n=10+10)

Allocs/op:
Pclntab_GC                    90.4k ± 0%     73.1k ± 0%    -19.11%  (p=0.000 n=10+10)

live-B:
Pclntab_GC                    29.1M ± 0%     29.2M ± 0%     +0.10%  (p=0.000 n=10+10)

binary sizes:
NEW: 18565600
OLD: 18532768

The size differences in the binary are caused by the increased size of
the Func objects, and (less likely) some extra alignment padding needed
as a result. This is probably the maximum increase in size we'll size
from the pclntab reworking.

Change-Id: Idd95a9b159fea46f7701cfe6506813b88257fbea
Reviewed-on: https://go-review.googlesource.com/c/go/+/246497
Run-TryBot: Jeremy Faller <jeremy@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Austin Clements <austin@google.com>

1 files changed, 14 insertions, 5 deletions

diff --git a/src/runtime/symtab.go b/src/runtime/symtab.go
index ddb5ea82b4..fbd9315522 100644
--- a/src/runtime/symtab.go
+++ b/src/runtime/symtab.go
@@ -334,14 +334,17 @@ const (
 	funcID_wrapper // any autogenerated code (hash/eq algorithms, method wrappers, etc.)
 )
 
-// PCHeader holds data used by the pclntab lookups.
+// pcHeader holds data used by the pclntab lookups.
 type pcHeader struct {
 	magic          uint32  // 0xFFFFFFFA
 	pad1, pad2     uint8   // 0,0
 	minLC          uint8   // min instruction size
 	ptrSize        uint8   // size of a ptr in bytes
 	nfunc          int     // number of functions in the module
+	nfiles         uint    // number of entries in the file tab.
 	funcnameOffset uintptr // offset to the funcnametab variable from pcHeader
+	cuOffset       uintptr // offset to the cutab variable from pcHeader
+	filetabOffset  uintptr // offset to the filetab variable from pcHeader
 	pclnOffset     uintptr // offset to the pclntab variable from pcHeader
 }
 
@@ -353,9 +356,10 @@ type pcHeader struct {
 type moduledata struct {
 	pcHeader     *pcHeader
 	funcnametab  []byte
+	cutab        []uint32
+	filetab      []byte
 	pclntable    []byte
 	ftab         []functab
-	filetab      []uint32
 	findfunctab  uintptr
 	minpc, maxpc uintptr
 
@@ -851,7 +855,12 @@ func funcfile(f funcInfo, fileno int32) string {
 	if !f.valid() {
 		return "?"
 	}
-	return gostringnocopy(&datap.pclntable[datap.filetab[fileno]])
+	// Make sure the cu index and file offset are valid
+	if fileoff := datap.cutab[f.cuOffset+uint32(fileno)]; fileoff != ^uint32(0) {
+		return gostringnocopy(&datap.filetab[fileoff])
+	}
+	// pcln section is corrupt.
+	return "?"
 }
 
 func funcline1(f funcInfo, targetpc uintptr, strict bool) (file string, line int32) {
@@ -865,7 +874,7 @@ func funcline1(f funcInfo, targetpc uintptr, strict bool) (file string, line int
 		// print("looking for ", hex(targetpc), " in ", funcname(f), " got file=", fileno, " line=", lineno, "\n")
 		return "?", 0
 	}
-	file = gostringnocopy(&datap.pclntable[datap.filetab[fileno]])
+	file = funcfile(f, fileno)
 	return
 }
 
@@ -1005,7 +1014,7 @@ type inlinedCall struct {
 	parent   int16  // index of parent in the inltree, or < 0
 	funcID   funcID // type of the called function
 	_        byte
-	file     int32 // fileno index into filetab
+	file     int32 // perCU file index for inlined call. See cmd/link:pcln.go
 	line     int32 // line number of the call site
 	func_    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)