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

[Wei Chen <Wei.Chen@xxxxxxx>]

Hi Simon,

> -----Original Message-----
> From: Simon Kuenzer <simon.kuenzer@xxxxxxxxx>
> Sent: 2018年7月12日 20:57
> To: Wei Chen <Wei.Chen@xxxxxxx>; minios-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: Kaly Xin <Kaly.Xin@xxxxxxx>; nd <nd@xxxxxxx>
> Subject: Re: [Minios-devel] [UNIKRAFT PATCHv4 14/43] build: Override default
> pie option of GCC if possible
> 
> 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?
> 

Hmm, I think we'd better keep this, because not all distributions will
enable the PIE by default. 

> > +$(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?
> 

Hmm, I checked the gcc code. The answer is NO, the enable-default-pie and
no-pie have been supported since gcc-6.1 at the same time

> > +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?
> 

Ok, it looks good to me.

> Thanks,
> 
> Simon
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