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Re: [PATCH] build: fix build failure with gcc 11.2 by disabling -fcf-pro

From: Paolo Bonzini
Subject: Re: [PATCH] build: fix build failure with gcc 11.2 by disabling -fcf-protection
Date: Fri, 18 Feb 2022 16:47:27 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.5.0

On 2/8/22 22:19, Vineet Gupta wrote:
When doing RV qemu builds with host gcc 11.2, ran into following build failure

| cc -MMD -MP -MT linuxboot_dma.o -MF ./linuxboot_dma.d -O2 -g -march=i486 
-Wall \
|   -Wstrict-prototypes -Wredundant-decls -Wundef -Wwrite-strings 
-Wmissing-prototypes \
|   -Wold-style-declaration -Wold-style-definition -Wtype-limits 
-Wformat-security \
|   -Wformat-y2k -Winit-self -Wignored-qualifiers -Wempty-body -Wnested-externs 
|   -Wendif-labels -Wexpansion-to-defined -Wimplicit-fallthrough=2 
-Wno-missing-include-dirs \
|   -Wno-shift-negative-value -Wno-psabi -fno-pie -ffreestanding -IQEMU/include 
|   -fno-stack-protector   -m16   -Wa,-32 \
|   -c QEMU/pc-bios/optionrom/linuxboot_dma.c -o linuxboot_dma.o
|cc1: error: ‘-fcf-protection’ is not compatible with this target

Signed-off-by: Vineet Gupta <vineetg@rivosinc.com>
This might be a crude fix to the problem
  pc-bios/optionrom/Makefile | 3 +++
  1 file changed, 3 insertions(+)

diff --git a/pc-bios/optionrom/Makefile b/pc-bios/optionrom/Makefile
index 5d55d25acca2..8f843ee803c1 100644
--- a/pc-bios/optionrom/Makefile
+++ b/pc-bios/optionrom/Makefile
@@ -22,6 +22,9 @@ override CFLAGS += $(CFLAGS_NOPIE) -ffreestanding 
  override CFLAGS += $(call cc-option, -fno-stack-protector)
  override CFLAGS += $(call cc-option, -m16)
+# issue with gcc 11.2
+override CFLAGS += $(call cc-option, -fcf-protection=none)
  ifeq ($(filter -m16, $(CFLAGS)),)
  # Attempt to work around compilers that lack -m16 (GCC <= 4.8, clang <= ??)
  # On GCC we add -fno-toplevel-reorder to keep the order of asm blocks with

This is a problem in the Ubuntu compiler that you're using. If -fcf-protection is not compatible with -m16, Ubuntu should not enable it instead of breaking -m16.

Besides, QEMU is not at all compatible with -fcf-protection, not just the ROMs. So it should be added to QEMU_CFLAGS in configure as well.


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