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

[Paolo Bonzini]

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 += $(CFLAGS_NOPIE) -ffreestanding 
> -I$(TOPSRC_DIR)/include
>   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.

Paolo