From f43312c974eaeb7301cb2638aa4ab05ed7ca4c44 Mon Sep 17 00:00:00 2001
From: Samuel Holland <samuel@sholland.org>
Date: Sat, 21 Aug 2021 19:54:02 -0500
Subject: [PATCH] ARM: Prevent the compiler from using NEON registers
For ARMv8-A, NEON is standard, so the compiler can use it even when no
special target flags are provided. For example, it can use stores from
NEON registers to zero-initialize large structures. GCC 11 decides to
do this inside the DRAM init code for the Allwinner H6.
However, GCC 11 has a bug where it generates misaligned NEON register
stores even with -mstrict-align. Since the MMU is not enabled this early
in SPL, the misaligned store causes an exception and breaks booting.
Work around this issue by restricting the compiler to using GPRs only,
not vector registers. This prevents any future surprises relating to
NEON use as well.
Signed-off-by: Samuel Holland <samuel@sholland.org>
Acked-by: Andre Przywara <andre.przywara@arm.com>
---
arch/arm/config.mk | 1 +
1 file changed, 1 insertion(+)
diff --git a/arch/arm/config.mk b/arch/arm/config.mk
index b684d8b416..b107b1af27 100644
--- a/arch/arm/config.mk
+++ b/arch/arm/config.mk
@@ -25,6 +25,7 @@ endif
PLATFORM_RELFLAGS += -fno-common -ffixed-r9
PLATFORM_RELFLAGS += $(call cc-option, -msoft-float) \
+ $(call cc-option,-mgeneral-regs-only) \
$(call cc-option,-mshort-load-bytes,$(call cc-option,-malignment-traps,))
# LLVM support
--
2.39.5