Re: [PATCH v3 1/8] config: Allow memory tagging to be enabled when configuring glibc

[Siddhesh Poyarekar <siddhesh@gotplt.org>]

On 11/23/20 9:12 PM, Richard Earnshaw via Libc-alpha wrote:
> 
> This patch adds the configuration machinery to allow memory tagging to be
> enabled from the command line via the configure option --enable-memory-tagging.
> 
> The current default is off, though in time we may change that once the API
> is more stable.
> ---
>   INSTALL             | 14 ++++++++++++++
>   config.h.in         |  3 +++
>   config.make.in      |  2 ++
>   configure           | 17 +++++++++++++++++
>   configure.ac        | 10 ++++++++++
>   manual/install.texi | 13 +++++++++++++
>   6 files changed, 59 insertions(+)
> 
> diff --git a/INSTALL b/INSTALL
> index 2b00f80df5..f2476df6c0 100644
> --- a/INSTALL
> +++ b/INSTALL
> @@ -142,6 +142,20 @@ if 'CFLAGS' is specified it must enable optimization.  For example:
>       non-CET processors.  '--enable-cet' has been tested for i686,
>       x86_64 and x32 on CET processors.
>  
> +'--enable-memory-tagging'
> +     Enable memory tagging support on architectures that support it.
> +     When the GNU C Library is built with this option then the resulting
> +     library will be able to control the use of tagged memory when
> +     hardware support is present by use of the tunable
> +     'glibc.memtag.enable'.  This includes the generation of tagged
> +     memory when using the 'malloc' APIs.
> +
> +     At present only AArch64 platforms with MTE provide this
> +     functionality, although the library will still operate (without
> +     memory tagging) on older versions of the architecture.
> +
> +     The default is to disable support for memory tagging.
> +
>  '--disable-profile'
>       Don't build libraries with profiling information.  You may want to
>       use this option if you don't plan to do profiling.
> diff --git a/config.h.in b/config.h.in
> index b823c8e080..2f4c626c19 100644
> --- a/config.h.in
> +++ b/config.h.in
> @@ -160,6 +160,9 @@
>  /* Define if __stack_chk_guard canary should be randomized at program startup.  */
>  #undef ENABLE_STACKGUARD_RANDOMIZE
>  
> +/* Define if memory tagging support should be enabled.  */
> +#undef _LIBC_MTAG
> +
>  /* Package description.  */
>  #undef PKGVERSION
>  
> diff --git a/config.make.in b/config.make.in
> index 1ac9417245..7ae27564fd 100644
> --- a/config.make.in
> +++ b/config.make.in
> @@ -84,6 +84,8 @@ mach-interface-list = @mach_interface_list@
>  
>  experimental-malloc = @experimental_malloc@
>  
> +memory-tagging = @memory_tagging@
> +
>  nss-crypt = @libc_cv_nss_crypt@
>  static-nss-crypt = @libc_cv_static_nss_crypt@
>  
> diff --git a/configure b/configure
> index 4795e721e5..d22654739f 100755
> --- a/configure
> +++ b/configure
> @@ -676,6 +676,7 @@ build_nscd
>  libc_cv_static_nss_crypt
>  libc_cv_nss_crypt
>  build_crypt
> +memory_tagging
>  experimental_malloc
>  enable_werror
>  all_warnings
> @@ -781,6 +782,7 @@ enable_all_warnings
>  enable_werror
>  enable_multi_arch
>  enable_experimental_malloc
> +enable_memory_tagging
>  enable_crypt
>  enable_nss_crypt
>  enable_systemtap
> @@ -1450,6 +1452,8 @@ Optional Features:
>                            architectures
>    --disable-experimental-malloc
>                            disable experimental malloc features
> +  --enable-memory-tagging enable memory tagging if supported by the
> +                          architecture [default=no]

I wonder if that phrasing implies that the flag is disabled if memory 
tagging is not supported by the architecture.  The description in 
INSTALL (Enable memory tagging support on architectures that support it) 
seems a bit more precise.

Siddhesh