Re: [PATCH] configure: Implement --enable-host-bind-now

[Iain Sandoe <idsandoe@googlemail.com>]

> On 27 Jun 2023, at 16:31, Marek Polacek via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
> 
> On Tue, Jun 27, 2023 at 01:39:16PM +0200, Martin Jambor wrote:
>> Hello,
>> 
>> On Tue, May 16 2023, Marek Polacek via Gcc-patches wrote:
>>> As promised in the --enable-host-pie patch, this patch adds another
>>> configure option, --enable-host-bind-now, which adds -z now when linking
>>> the compiler executables in order to extend hardening.  BIND_NOW with RELRO
>>> allows the GOT to be marked RO; this prevents GOT modification attacks.
>>> 
>>> This option does not affect linking of target libraries; you can use
>>> LDFLAGS_FOR_TARGET=-Wl,-z,relro,-z,now to enable RELRO/BIND_NOW.
>>> 
>>> With this patch:
>>> $ readelf -Wd cc1{,plus} | grep FLAGS
>>> 0x000000000000001e (FLAGS)              BIND_NOW
>>> 0x000000006ffffffb (FLAGS_1)            Flags: NOW PIE
>>> 0x000000000000001e (FLAGS)              BIND_NOW
>>> 0x000000006ffffffb (FLAGS_1)            Flags: NOW PIE
>>> 
>>> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
>>> 
>>> c++tools/ChangeLog:
>>> 
>>> 	* configure.ac (--enable-host-bind-now): New check.
>>> 	* configure: Regenerate.
>>> 
>>> gcc/ChangeLog:
>>> 
>>> 	* configure.ac (--enable-host-bind-now): New check.  Add
>>> 	-Wl,-z,now to LD_PICFLAG if --enable-host-bind-now.
>>> 	* configure: Regenerate.
>>> 	* doc/install.texi: Document --enable-host-bind-now.
>>> 
>>> lto-plugin/ChangeLog:
>>> 
>>> 	* configure.ac (--enable-host-bind-now): New check.  Link with
>>> 	-z,now.
>>> 	* configure: Regenerate.
>> 
>> Our reconfiguration checking script complains about a missing hunk in
>> lto-plugin/Makefile.in:
>> 
>> diff --git a/lto-plugin/Makefile.in b/lto-plugin/Makefile.in
>> index cb568e1e09f..f6f5b020ff5 100644
>> --- a/lto-plugin/Makefile.in
>> +++ b/lto-plugin/Makefile.in
>> @@ -298,6 +298,7 @@ datadir = @datadir@
>> datarootdir = @datarootdir@
>> docdir = @docdir@
>> dvidir = @dvidir@
>> +enable_host_bind_now = @enable_host_bind_now@
>> exec_prefix = @exec_prefix@
>> gcc_build_dir = @gcc_build_dir@
>> get_gcc_base_ver = @get_gcc_base_ver@
>> 
>> 
>> I am somewhat puzzled why the line is not missing in any of the other
>> Makefile.in files.  Can you please check whether that is the only thing
>> that is missing (assuming it is actually missing)?
> 
> Arg, once again, I'm sorry.  I don't know how this happened.  It would
> be trivial to fix it but since
> 
> commit 4a48a38fa99f067b8f3a3d1a5dc7a1e602db351f
> Author: Eric Botcazou <ebotcazou@adacore.com>
> Date:   Wed Jun 21 18:19:36 2023 +0200
> 
>    ada: Fix build of GNAT tools
> 
> the build with Ada included fails with --enable-host-pie.  So that needs
> to be fixed first.
> 
> Eric, I'm not asking you to fix that, but I'm curious, what did the
> commit above fix?  The patch looks correct; I'm just puzzled why I
> hadn't seen any build failures.

I am also curious as to why we do not need some logic to do a similar job
in gcc-interface/Make-lang.in:

ifeq ($(STAGE1),True)
  ADA_INCLUDES=$(COMMON_ADA_INCLUDES)
  adalib=$(dir $(shell $(CC) -print-libgcc-file-name))adalib
  GNATLIB=$(adalib)/$(if $(wildcard $(adalib)/libgnat.a), libgnat.a,libgnat.so) $(STAGE1_LIBS)
else

^^^ I would expect us to need to switch to libgnat_pic.a when we are building a PIE exe.

Iain

> The --enable-host-pie patch has been a nightmare :(.
> 
> Marek