From 9d673bf1db091db5660e941c1c7d2fd40e268d44 Mon Sep 17 00:00:00 2001
From: Jeremy Faller <jeremy@golang.org>
Date: Thu, 13 Feb 2020 10:38:33 -0500
Subject: [PATCH] [dev.link] cmd/link: use RO memory (when avail) in elf loader

Recreation of CL 206139 in the new symbol hierarchy.

Change-Id: Ic20c5c1b5db8f7eadf4c6ee4638e3c1a4e10ef3a
Reviewed-on: https://go-review.googlesource.com/c/go/+/219317
Run-TryBot: Jeremy Faller <jeremy@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
---
 src/cmd/link/internal/amd64/asm.go     |  1 +
 src/cmd/link/internal/loadelf/ldelf.go | 33 +++++++++++++-------------
 2 files changed, 18 insertions(+), 16 deletions(-)

diff --git a/src/cmd/link/internal/amd64/asm.go b/src/cmd/link/internal/amd64/asm.go
index 0f0dcc4f42..f6b13c4abc 100644
--- a/src/cmd/link/internal/amd64/asm.go
+++ b/src/cmd/link/internal/amd64/asm.go
@@ -158,6 +158,7 @@ func adddynrel(ctxt *ld.Link, s *sym.Symbol, r *sym.Reloc) bool {
 		if targ.Type != sym.SDYNIMPORT {
 			// have symbol
 			if r.Off >= 2 && s.P[r.Off-2] == 0x8b {
+				makeWritable(s)
 				// turn MOVQ of GOT entry into LEAQ of symbol itself
 				s.P[r.Off-2] = 0x8d
 
diff --git a/src/cmd/link/internal/loadelf/ldelf.go b/src/cmd/link/internal/loadelf/ldelf.go
index d3cf4aed7b..2eabefd4fb 100644
--- a/src/cmd/link/internal/loadelf/ldelf.go
+++ b/src/cmd/link/internal/loadelf/ldelf.go
@@ -270,19 +270,20 @@ type ElfSymBytes64 struct {
 }
 
 type ElfSect struct {
-	name    string
-	nameoff uint32
-	type_   uint32
-	flags   uint64
-	addr    uint64
-	off     uint64
-	size    uint64
-	link    uint32
-	info    uint32
-	align   uint64
-	entsize uint64
-	base    []byte
-	sym     loader.Sym
+	name        string
+	nameoff     uint32
+	type_       uint32
+	flags       uint64
+	addr        uint64
+	off         uint64
+	size        uint64
+	link        uint32
+	info        uint32
+	align       uint64
+	entsize     uint64
+	base        []byte
+	readOnlyMem bool // Is this section in readonly memory?
+	sym         loader.Sym
 }
 
 type ElfObj struct {
@@ -600,7 +601,6 @@ func Load(l *loader.Loader, arch *sys.Arch, localSymVersion int, f *bio.Reader,
 		sect := &elfobj.sect[i]
 		if is64 != 0 {
 			var b ElfSectBytes64
-
 			if err := binary.Read(f, e, &b); err != nil {
 				return errorf("malformed elf file: %v", err)
 			}
@@ -750,6 +750,7 @@ func Load(l *loader.Loader, arch *sys.Arch, localSymVersion int, f *bio.Reader,
 
 		sb.SetSize(int64(sect.size))
 		sb.SetAlign(int32(sect.align))
+		sb.SetReadOnly(sect.readOnlyMem)
 
 		sect.sym = sb.Sym()
 	}
@@ -1016,9 +1017,9 @@ func elfmap(elfobj *ElfObj, sect *ElfSect) (err error) {
 		return err
 	}
 
-	sect.base = make([]byte, sect.size)
 	elfobj.f.MustSeek(int64(uint64(elfobj.base)+sect.off), 0)
-	if _, err := io.ReadFull(elfobj.f, sect.base); err != nil {
+	sect.base, sect.readOnlyMem, err = elfobj.f.Slice(uint64(sect.size))
+	if err != nil {
 		return fmt.Errorf("short read: %v", err)
 	}