Re: [PATCH, libmpx, i386, PR driver/65444] Pass '-z bndplt' when building dynamic objects with MPX

[Ilya Enkovich <enkovich dot gnu at gmail dot com>]

On 05 Apr 19:44, Sandra Loosemore wrote:
> On 04/03/2015 01:34 PM, Joseph Myers wrote:
> >On Tue, 31 Mar 2015, Ilya Enkovich wrote:
> >
> >>+library.  It also passes '-z bndplt' to a linker in case it supports this
> >>+option (which is checked on libmpx configuration).  Note that old versions
> >>+of linker may ignore option.  Gold linker doesn't support '-z bndplt'
> >>+option.  With no '-z bndplt' support in linker all calls to dynamic libraries
> >>+lose passed bounds reducing overall protection level.  It's highly
> >>+recommended to use linker with '-z bndplt' support.  In case such linker
> >>+is not available it is adviced to always use @option{-static-libmpxwrappers}
> >>+for better protection level or use @option{-static} to completely avoid
> >>+external calls to dynamic libraries.  MPX-based instrumentation
> >
> >Use @samp{-z bndplt} rather than '' quoting (but Sandra may have further
> >advice on the substance of this documentation).
> 
> To tell the truth, I can't figure out what this means from a user
> perspective.  How does a user know whether the linker option is
> being ignored, or if they have a new enough linker?  If the linker
> available at configuration time doesn't support the option, does
> that mean the option will never be passed and users will never know
> that there are gaping holes in the pointer bounds checking?
> 
> My suggestion would be to pass the option unconditionally and make
> the documentation say something like

This option was rejected.

> 
> It also passes @option{-z bndplt} to the linker.  LD version xxx or
> later is required to use this feature.  If no linker support for
> @option{-z bndplt} is available, you should link with
> @option{-static-libmpxwrappers} or @option{-static} instead;
> otherwise calls to dynamic libraries lose bounds checking
> protection.
> 
> ... where you need to fill in "version xxx" appropriately.
> 
> -Sandra
> 

Thank you for comments.  Here is a doc update I'm going to install if nobody objects.

Ilya
--
2015-04-06  Ilya Enkovich  <ilya.enkovich@intel.com>

	* doc/invoke.texi (-fcheck-pointer-bounds): Fix
	formatting.


diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index c058710..72b9578 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -5858,12 +5858,12 @@ a runtime library to enable MPX in hardware and handle bounds
 violation signals.  By default when @option{-fcheck-pointer-bounds}
 and @option{-mmpx} options are used to link a program, the GCC driver
 links against the @file{libmpx} runtime library and @file{libmpxwrappers}
-library.  It also passes '-z bndplt' to a linker in case it supports this
-option (which is checked on libmpx configuration).  Note that old versions
-of linker may ignore option.  Gold linker doesn't support '-z bndplt'
-option.  With no '-z bndplt' support in linker all calls to dynamic libraries
-lose passed bounds reducing overall protection level.  It's highly
-recommended to use linker with '-z bndplt' support.  In case such linker
+library.  It also passes @option{-z bndplt} to a linker in case it supports
+this option (which is checked on libmpx configuration).  LD supports it starting
+from version 2.25.  Gold linker doesn't support @option{-z bndplt}
+option.  With no @option{-z bndplt} support in a linker all calls to dynamic
+libraries lose passed bounds reducing overall protection level.  It's highly
+recommended to use linker with @option{-z bndplt} support.  In case such linker
 is not available it is adviced to always use @option{-static-libmpxwrappers}
 for better protection level or use @option{-static} to completely avoid
 external calls to dynamic libraries.  MPX-based instrumentation