Re: [PATCH] m4/pma.m4: disable PIE in both CFLAGS and LDFLAGS consistently

[Sergei Trofimovich]

On Wed, 11 Jan 2023 00:29:17 -0700
arnold@skeeve.com wrote:

> Hi.
> 
> Thank you for the report.  I will get this into the repo in the next
> few days.
> 
> Arnold
> 
> Sergei Trofimovich <slyich@gmail.com> wrote:
> 
> > In https://github.com/NixOS/nixpkgs/pull/207478#issuecomment-1378021841
> > Alyssa noticed that gawk build fails on x86_64-unknown-linux-musl target
> > in nixpkgs as:
> >
> >     ld: .../x86_64-unknown-linux-musl/11.3.0/crtbegin.o:
> >         relocation R_X86_64_32 against hidden symbol `__TMC_END__'
> >         can not be used when making a PIE object
> >     ld: failed to set dynamic section sizes: bad value

My apologies, underlying error happened due to downstream error of passing
-no-pie to gcc and passing -pie to ld. Hence the failure to handle
non-relocatable objects from crtbegin.o into a PIE binary (it should not
have been PIE in the first place)!

ld should always succeed linking -no-pie executables out of -fPIE (or -fPIC)
.o files. Thus it's a downstream failure. It if does not it's a toolchain bug.

I think this patch is still a correct thing to do, but it's not fundamental
to fix the failure. Just a minor optimization.

> > This happens because both compiler (CFLAGS=-fPIE) and linker
> > (LDFLAGS=-pie) enable PIE by default.
> >
> > As a result just disabling linker flag is not enough and `ld`
> > detects unresolvable dynamic relocations for non-PIE binary.
> >
> > The change disables PIE for both CFLAGS and LDFLAGS.
> > ---
> >  m4/pma.m4 | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/m4/pma.m4 b/m4/pma.m4
> > index c0535a26..73f6b316 100644
> > --- a/m4/pma.m4
> > +++ b/m4/pma.m4
> > @@ -19,9 +19,13 @@ then
> >             use_persistent_malloc=yes
> >             case $host_os in
> >             linux-*)
> > +                   # Guard against toolchains that default to CFLAGS=-fPIE 
> > LDFLAGS=-pie
> >                     AX_CHECK_COMPILE_FLAG([-no-pie],
> >                             [LDFLAGS="${LDFLAGS} -no-pie"
> >                             export LDFLAGS])
> > +                   AX_CHECK_COMPILE_FLAG([-fno-PIE],
> > +                           [CFLAGS="${CFLAGS} -fno-PIE"
> > +                           export CFLAGS])
> >                     ;;
> >             *darwin*)
> >                     # 27 November 2022: PMA only works on Intel.
> > -- 
> > 2.38.1
> >  

-- 

  Sergei

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