Add support for -fstack-protector in native builds

-fstack-protector only needs a small amount of runtime
support to work on native builds. It increases code size
by ~1.5% on ARM/MIPS; -fstack-protector-strong adds 3-4%.
This is disabled by default and must be enabled by passing
'--with-stack-protector' to configure.

Change-Id: If952e711d3673c9b469895f08c7bff70b3d95df6

apps/plugins/lib/gcc-support.c

@@ -34,6 +34,15 @@ void __aeabi_ldiv0(void) __attribute__((alias("__div0")));
 #endif
 #endif
 
+#if defined(USE_STACK_PROTECTOR)
+const uint32_t __stack_chk_guard = 0x3BADC0DE;
+
+void __stack_chk_fail(void)
+{
+    rb->panicf("plugin smashed stack");
+}
+#endif
+
 void *memcpy(void *dest, const void *src, size_t n)
 {
     return rb->memcpy(dest, src, n);

firmware/asm/SOURCES

@@ -65,3 +65,7 @@ lcd-as-memframe.c
 #endif /* CPU_ARM */
 #endif /* LCD_DEPTH */
 #endif
+
+#if defined(USE_STACK_PROTECTOR)
+stack-protector.c
+#endif

firmware/asm/stack-protector.c

@@ -0,0 +1,29 @@
+/***************************************************************************
+*             __________               __   ___.
+*   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
+*   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
+*   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
+*   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
+*                     \/            \/     \/    \/            \/
+* $Id$
+*
+* Copyright (C) 2026 by Aidan MacDonald
+*
+* This program is free software; you can redistribute it and/or
+* modify it under the terms of the GNU General Public License
+* as published by the Free Software Foundation; either version 2
+* of the License, or (at your option) any later version.
+*
+* This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+* KIND, either express or implied
+*
+****************************************************************************/
+#include "panic.h"
+#include <stdint.h>
+
+const uint32_t __stack_chk_guard = 0x1BADC0DE;
+
+void __stack_chk_fail(void)
+{
+    panicf("stack smashing detected");
+}

lib/rbcodec/codecs/codec_crt0.c

@@ -78,3 +78,12 @@ void __attribute__((naked)) __div0(void)
     asm volatile("bx %0" : : "r"(ci->__div0));
 }
 #endif
+
+#if defined(USE_STACK_PROTECTOR)
+const uint32_t __stack_chk_guard = 0x2BADC0DE;
+
+void __stack_chk_fail(void)
+{
+    ci->panicf("codec smashed stack");
+}
+#endif

tools/configure

@@ -1531,6 +1531,9 @@ help() {
     --with-address-sanitizer
                       Enables the AddressSanitizer feature. Forces SDL threads.
     --with-ubsan      Enables the UB Sanitizer feature.  Forces SDL threads.
+    --with-stack-protector[=MODE]
+                      Enable -fstack-protector-MODE option. With no MODE,
+                      enables the normal -fstack-protector option.
     --32-bit          Force a 32-bit simulator (use with --sdl-threads for duke3d)
     --prefix          Target installation directory
     --compiler-prefix Override compiler prefix (inherently dangerous)
@@ -1557,6 +1560,7 @@ ARG_THREAD_SUPPORT=
 ARG_32BIT=
 ARG_ADDR_SAN=
 ARG_UBSAN=
+ARG_STACK_PROTECTOR=
 ARG_PLUGINS=
 err=
 for arg in "$@"; do
@@ -1583,6 +1587,8 @@ for arg in "$@"; do
                       ARG_THREAD_SUPPORT=0;;
         --with-address-sanitizer) ARG_ADDR_SAN=1;;
         --with-ubsan) ARG_UBSAN=1;;
+        --with-stack-protector=*) ARG_STACK_PROTECTOR=`echo "$arg" | cut -d = -f 2`;;
+        --with-stack-protector) ARG_STACK_PROTECTOR=default;;
         --prefix=*)   ARG_PREFIX=`echo "$arg" | cut -d = -f 2`;;
         --compiler-prefix=*)   ARG_COMPILER_PREFIX=`echo "$arg" | cut -d = -f 2`;;
 		--help)       help;;
@@ -4694,6 +4700,17 @@ if [ "$ARG_RBDIR" != "" ]; then
   echo "Using alternate rockbox dir: ${rbdir}"
 fi
 
+if [ "$ARG_STACK_PROTECTOR" != "" ]; then
+    echo "Stack protector mode: $ARG_STACK_PROTECTOR"
+    extradefines="$extradefines -DUSE_STACK_PROTECTOR"
+
+    if [ "$ARG_STACK_PROTECTOR" = "default" ]; then
+        GCCOPTS="$GCCOPTS -fstack-protector"
+    else
+        GCCOPTS="$GCCOPTS -fstack-protector-${ARG_STACK_PROTECTOR}"
+    fi
+fi
+
 cat > autoconf.h.new <<EOF
 /* This header was made by configure */
 #ifndef __BUILD_AUTOCONF_H