cmd/internal/objfile, debug/gosym: use the address of runtime.text as textStart

Tools like objdump uses the pcln table to find the line number of
a given PC. For a PIE binary, at least in some cases such as on
macOS 12 with ld64-711, the table contains unrelocated address,
which does not match the address in the symbol table, causing the
lookup to fail.

In Go 1.18 the pcln table is essentually position independent,
except the start PC. Instead of reading the static content from
the table, use the PC of runtime.text from the symbol table.

While here, change the type of textStart to uint64. What matters
here is the word size of the target program, not the host, so it
shouldn't be uintptr.

Fixes #49700.

Change-Id: I517d79be7ba02dd4dd0275e75a11a136b08d76cd
Reviewed-on: https://go-review.googlesource.com/c/go/+/366695
Trust: Cherry Mui <cherryyz@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>

src/cmd/internal/objfile/objfile.go

@@ -152,6 +152,15 @@ func (e *Entry) PCLineTable() (Liner, error) {
 	if err != nil {
 		return nil, err
 	}
+	syms, err := e.raw.symbols()
+	if err == nil {
+		for _, s := range syms {
+			if s.Name == "runtime.text" {
+				textStart = s.Addr
+				break
+			}
+		}
+	}
 	return gosym.NewTable(symtab, gosym.NewLineTable(pclntab, textStart))
 }