Implement link-time optimization safe explicit_bzero()?

[Manuel López-Ibáñez]

On 12/02/16 06:21, Sebastian Huber wrote:
>> If I were to tackle this problem, I would try first to implement a
>> __builtin_explicit_bzero() directly in GCC such that GCC will know exactly how
>> to handle it. This would be faster, safer and more portable than any trick you
>> may get working now (since LTO keeps improving), and it will provide the basis
>> for a gnu libc implementation.
>
> Ok, since I am not a compiler expert, I need an example for this.  My first try was to search for the memset_s() builtin. However, this doesn't seem to exist.  Is memset_s() supported at all by GCC currently?

See https://gcc.gnu.org/git/?p=gcc.git;a=blob_plain;f=gcc/builtins.def;hb=HEAD

memset_s is not there, so I guess it is not provided as a builtin, but 
implemented by the C library. Probably it is not LTO-safe either.

But there is:

DEF_EXT_LIB_BUILTIN (BUILT_IN_BZERO, "bzero", BT_FN_VOID_PTR_SIZE, 
ATTR_NOTHROW_LEAF_LIST)

No need to be a compiler expert to hack on GCC. And I'm sure you are more 
qualified than I am.

In any case, these questions are more appropriate for gcc@ and gcc-patches@. 
Few devs read gcc-help@

>> Of course, there is the question of whether explicit_bzero() or similar
>> functions are a solution at all to any problem
>> (https://sourceware.org/ml/libc-alpha/2016-01/msg00208.html)
>
> Would a builtin not fix this issue? I am not sure if I understood this post at all.

Sorry, wrong link. Correct one: 
https://gcc.gnu.org/ml/gcc-help/2014-10/msg00061.html

Cheers,

Manuel.