Re: [Minios-devel] [UNIKRAFT PATCHv4 14/43] build: Override default pie option of GCC if possible

[Simon Kuenzer <simon.kuenzer@xxxxxxxxx>]

Hi Wei,

On 06.07.2018 11:03, Wei Chen wrote:
> On recent debian distributions (Debian/Ubuntu), the GCC enabled
> "--enable-default-pie" configuration option by default. This will
> case Unikraft link failed on debian/ubuntu platforms.
> In commit:
> "build: Add -no-pie to GCC flags"
> "cc7eb555080775cf2cb4a595a07b6121ff0f7361"
> I have added -no-pie to GCC flags directly to override the default
> pie option. But as Wei Liu reminded, old version GCC doesn't
> support -no-pie option.
>
> So in this patch, I checked the enbale-default-pie option and
> GCC version, and then added -no-pie to override it.
>
> Signed-off-by: Wei Chen <Wei.Chen@xxxxxxx>
> ---
>   Makefile.uk | 22 +++++++++++++++++-----
>   1 file changed, 17 insertions(+), 5 deletions(-)
>
> diff --git a/Makefile.uk b/Makefile.uk
> index b3938d0..cea7ac3 100644
> --- a/Makefile.uk
> +++ b/Makefile.uk
> @@ -4,15 +4,15 @@
>   #
>   
> ################################################################################
>   
> -ASFLAGS     += -U __linux__ -U __FreeBSD__ -U __sun__ -D__ASSEMBLY__ -no-pie
> +ASFLAGS     += -U __linux__ -U __FreeBSD__ -U __sun__ -D__ASSEMBLY__
>   ASINCLUDES  += -nostdinc -nostdlib -I$(CONFIG_UK_BASE)/include
>   
> -CFLAGS      += -U __linux__ -U __FreeBSD__ -U __sun__ -no-pie
> +CFLAGS      += -U __linux__ -U __FreeBSD__ -U __sun__
>   CFLAGS      += -fno-stack-protector -fno-omit-frame-pointer -fno-tree-sra
>   CFLAGS      += -Wall -Wextra
>   CINCLUDES   += -nostdinc -nostdlib -I$(CONFIG_UK_BASE)/include
>   
> -CXXFLAGS    += -U __linux__ -U __FreeBSD__ -U __sun__ -no-pie
> +CXXFLAGS    += -U __linux__ -U __FreeBSD__ -U __sun__
>   CXXFLAGS    += -fno-stack-protector -fno-omit-frame-pointer -fno-tree-sra
>   CXXFLAGS    += -Wall -Wextra
>   CXXINCLUDES += -nostdinc -nostdlib -I$(CONFIG_UK_BASE)/include
> @@ -20,8 +20,8 @@ CXXINCLUDES += -nostdinc -nostdlib -I$(CONFIG_UK_BASE)/include
>   # Set the text and data sections to be readable and writable. Also,
>   # do not page-align the data segment. If the output format supports
>   # Unix style magic numbers, mark the output as OMAGIC.
> -LIBLDFLAGS  += -nostdinc -nostdlib -Wl,--omagic -Wl,-r -no-pie
> -LDFLAGS     += -nostdinc -nostdlib -Wl,--omagic -Wl,--build-id=none -no-pie
> +LIBLDFLAGS  += -nostdinc -nostdlib -Wl,--omagic -Wl,-r
> +LDFLAGS     += -nostdinc -nostdlib -Wl,--omagic -Wl,--build-id=none
>   
>   CFLAGS-$(CONFIG_OPTIMIZE_NONE)            += -O0 -fno-optimize-sibling-calls -fno-tree-vectorize
>   CXXFLAGS-$(CONFIG_OPTIMIZE_NONE)          += -O0 -fno-optimize-sibling-calls 
> -fno-tree-vectorize
> @@ -56,3 +56,15 @@ endif
>   ASFLAGS  += -DUK_VERSION=$(UK_VERSION).$(UK_SUBVERSION) 
> -DUK_FULLVERSION=$(UK_FULLVERSION) -DUK_CODENAME="$(UK_CODENAME)"
>   CFLAGS   += -DUK_VERSION=$(UK_VERSION).$(UK_SUBVERSION) 
> -DUK_FULLVERSION=$(UK_FULLVERSION) -DUK_CODENAME="$(UK_CODENAME)"
>   CXXFLAGS += -DUK_VERSION=$(UK_VERSION).$(UK_SUBVERSION) 
> -DUK_FULLVERSION=$(UK_FULLVERSION) -DUK_CODENAME="$(UK_CODENAME)"
> +
> +# Check whether the pie option is enabled by default. If possible,
> +# add -no-pie to link flags to override default pie option.
> +PIE_ON = $(shell $(CC) -v 2>&1 | grep -Fo "enable-default-pie")
> +ifneq ($(PIE_ON),)
Hum, do you think we really need this check?

> +$(call error_if_gcc_version_lt,6,1)
..and this crash if GCC was configured with enable-default-pie. Is it 
the case that GCC < 6.1 can have this configuration option but does not 
provide the runtime option to disable it again with -no-pie?
> +ASFLAGS     += -no-pie
> +CFLAGS      += -no-pie
> +CXXFLAGS    += -no-pie
> +LIBLDFLAGS  += -no-pie
> +LDFLAGS     += -no-pie
> +endif
If yes, we need to do it in the way you propose. Otherwise, I would just 
add the -no-pie option irregardless how GCC was configured. Just set add 
the flag starting with the first GCC version that it provides. Something 
like:
ASFLAGS-$(call gcc_version_ge,6,1)    += -no-pie
CFLAGS-$(call gcc_version_ge,6,1)     += -no-pie
CXXFLAGS-$(call gcc_version_ge,6,1)   += -no-pie
LIBLDFLAGS-$(call gcc_version_ge,6,1) += -no-pie
LDFLAGS-$(call gcc_version_ge,6,1)    += -no-pie

What do you think?

Thanks,

Simon

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