From 54383f684f7126b8fb7e2a80981221ff174735e4 Mon Sep 17 00:00:00 2001
From: Marius Vikhammer <marius.vikhammer@espressif.com>
Date: Mon, 29 Mar 2021 12:18:25 +0800
Subject: [PATCH] soc: add dummy bytes to ensure instr prefetch always valid

The CPU might prefetch instructions, which means it in some cases
will try to fetch instruction located after the last instruction in
flash.text.

Add dummy bytes to ensure fetching these wont result in an error,
 e.g. MMU exceptions
---
 .../bootloader/subproject/main/ld/esp32/bootloader.ld     | 8 ++++++++
 .../bootloader/subproject/main/ld/esp32s2/bootloader.ld   | 8 ++++++++
 components/esp32/ld/esp32.project.ld.in                   | 8 ++++++++
 components/esp32s2/ld/esp32s2.project.ld.in               | 8 ++++++++
 4 files changed, 32 insertions(+)

diff --git a/components/bootloader/subproject/main/ld/esp32/bootloader.ld b/components/bootloader/subproject/main/ld/esp32/bootloader.ld
index 6d1264687b..dd2e887e3c 100644
--- a/components/bootloader/subproject/main/ld/esp32/bootloader.ld
+++ b/components/bootloader/subproject/main/ld/esp32/bootloader.ld
@@ -164,6 +164,14 @@ SECTIONS
     *(.fini.literal)
     *(.fini)
     *(.gnu.version)
+
+    /** CPU will try to prefetch up to 16 bytes of
+      * of instructions. This means that any configuration (e.g. MMU, PMS) must allow
+      * safe access to up to 16 bytes after the last real instruction, add
+      * dummy bytes to ensure this
+      */
+    . += 16;
+
     _text_end = ABSOLUTE(.);
     _etext = .;
   } > iram_seg
diff --git a/components/bootloader/subproject/main/ld/esp32s2/bootloader.ld b/components/bootloader/subproject/main/ld/esp32s2/bootloader.ld
index ec08995e1e..93f1cc7eb0 100644
--- a/components/bootloader/subproject/main/ld/esp32s2/bootloader.ld
+++ b/components/bootloader/subproject/main/ld/esp32s2/bootloader.ld
@@ -150,6 +150,14 @@ SECTIONS
     *(.fini.literal)
     *(.fini)
     *(.gnu.version)
+
+    /** CPU will try to prefetch up to 16 bytes of
+      * of instructions. This means that any configuration (e.g. MMU, PMS) must allow
+      * safe access to up to 16 bytes after the last real instruction, add
+      * dummy bytes to ensure this
+      */
+    . += 16;
+
     _text_end = ABSOLUTE(.);
     _etext = .;
   } > iram_seg
diff --git a/components/esp32/ld/esp32.project.ld.in b/components/esp32/ld/esp32.project.ld.in
index da082d014b..d5a7b401b8 100644
--- a/components/esp32/ld/esp32.project.ld.in
+++ b/components/esp32/ld/esp32.project.ld.in
@@ -335,6 +335,14 @@ SECTIONS
     *(.fini.literal)
     *(.fini)
     *(.gnu.version)
+
+    /** CPU will try to prefetch up to 16 bytes of
+      * of instructions. This means that any configuration (e.g. MMU, PMS) must allow
+      * safe access to up to 16 bytes after the last real instruction, add
+      * dummy bytes to ensure this
+      */
+    . += 16;
+
     _text_end = ABSOLUTE(.);
     _etext = .;
 
diff --git a/components/esp32s2/ld/esp32s2.project.ld.in b/components/esp32s2/ld/esp32s2.project.ld.in
index 4da0db6123..878339850c 100644
--- a/components/esp32s2/ld/esp32s2.project.ld.in
+++ b/components/esp32s2/ld/esp32s2.project.ld.in
@@ -321,6 +321,14 @@ SECTIONS
     *(.fini.literal)
     *(.fini)
     *(.gnu.version)
+
+    /** CPU will try to prefetch up to 16 bytes of
+      * of instructions. This means that any configuration (e.g. MMU, PMS) must allow
+      * safe access to up to 16 bytes after the last real instruction, add
+      * dummy bytes to ensure this
+      */
+    . += 16;
+
     _text_end = ABSOLUTE(.);
     _instruction_reserved_end = ABSOLUTE(.);
     _etext = .;