runtime: make pcln table check not trigger next to foreign code

Foreign code can be arbitrarily aligned,
so the function before it can have
arbitrarily much padding.
We can't call pcvalue on values in the padding.

Fixes #11653.

Change-Id: I7d57f813ae5a2409d1520fcc909af3eeef2da131
Reviewed-on: https://go-review.googlesource.com/12550Reviewed-by: Rob Pike <r@golang.org>

src/runtime/symtab.go

@@ -134,11 +134,20 @@ func moduledataverify1(datap *moduledata) {
 			// The very end might be just padding that is not covered by the tables.
 			// No architecture rounds function entries to more than 16 bytes,
 			// but if one came along we'd need to subtract more here.
-			end := datap.ftab[i+1].entry - 16
-			if end < datap.ftab[i].entry {
-				end = datap.ftab[i].entry
-			}
+			// But don't use the next PC if it corresponds to a foreign object chunk
+			// (no pcln table, f2.pcln == 0). That chunk might have an alignment
+			// more than 16 bytes.
 			f := (*_func)(unsafe.Pointer(&datap.pclntable[datap.ftab[i].funcoff]))
+			end := f.entry
+			if i+1 < nftab {
+				f2 := (*_func)(unsafe.Pointer(&datap.pclntable[datap.ftab[i+1].funcoff]))
+				if f2.pcln != 0 {
+					end = f2.entry - 16
+					if end < f.entry {
+						end = f.entry
+					}
+				}
+			}
 			pcvalue(f, f.pcfile, end, true)
 			pcvalue(f, f.pcln, end, true)
 			pcvalue(f, f.pcsp, end, true)