From 9901603e18524c4c52fd1dd47bda4ab4016628fc Mon Sep 17 00:00:00 2001
From: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Date: Thu, 10 Sep 2020 11:37:33 +0200
Subject: [PATCH] Pass -fno-builtin to fix build with gcc 10

gcc 10, if it recognizes some hand-written code that looks like
memcpy, will generate a call to memcpy().

For example:

        while (dst < &_end_data) {
                *dst++ = *src++;
        }

gets recognized as such. However, in the context of bare-metal code,
having a call to memcpy() in the C library doesn't work. So we fix
that by disabling builtins.

Fixes:

/home/thomas/projets/buildroot/output/host/opt/ext-toolchain/bin/../arm-buildroot-uclinux-uclibcgnueabi/bin/ld.real: stm32f429i-disco.o: in function `reset':
stm32f429i-disco.c:(.text.reset+0x1a): undefined reference to `memcpy'
/home/thomas/projets/buildroot/output/host/opt/ext-toolchain/bin/../arm-buildroot-uclinux-uclibcgnueabi/bin/ld.real: stm32f429i-disco.c:(.text.reset+0x34): undefined reference to `memset'
make[1]: *** [Makefile:26: stm32f429i-disco] Error 1

Upstream: https://github.com/mcoquelin-stm32/afboot-stm32/pull/11
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
---
 Makefile | 1 +
 1 file changed, 1 insertion(+)

diff --git a/Makefile b/Makefile
index f699176..1e8557d 100644
--- a/Makefile
+++ b/Makefile
@@ -13,6 +13,7 @@ DTB_ADDR?=0x08004000
 CFLAGS := -mthumb -mcpu=cortex-m4
 CFLAGS += -ffunction-sections -fdata-sections
 CFLAGS += -Os -std=gnu99 -Wall
+CFLAGS += -fno-builtin
 LINKERFLAGS := -nostartfiles --gc-sections
 
 obj-y += gpio.o mpu.o qspi.o start_kernel.o
-- 
2.35.1