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

["Richard Earnshaw (lists)" <Richard.Earnshaw@arm.com>]

On 25/11/2020 15:05, Siddhesh Poyarekar wrote:
> 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

I'd be happy to change that to "Enable memory tagging on supported
architectures [default=no]".

R.