Re: [PATCH] Revert Intel CET changes to __jmp_buf_tag (Bug 22743)

[Florian Weimer <fweimer at redhat dot com>]

On 01/25/2018 06:33 AM, H.J. Lu wrote:

> Please don't revert my patch.  Please try this patch:
>
> https://sourceware.org/git/?p=glibc.git;a=commit;h=4b7fc470a6740808b41502d7431f91805e272d26
>
> instead.  I will clean it up and submit it tomorrow.

I don't see how adding a symbol version to pthread_create helps to solve 
the general case.  Callers of pthread_register_cancel and pthread_create 
are often compiled at different times.  Not everyone does a mass rebuild 
each time they switch to a new glibc version.

I still think you are over-engineering this.  The pad array has still an 
unused member (the last one).  Just change sigsetjmp to store the shadow 
pointer in that location, then the old and new setjmp will work with the 
current stack layout.  As far as I can tell, there are only 64 signals, 
so you don't even have to change the location of the signal mask.

Furthermore, nothing in the toolchain prevents people from compiling 
CET-marked binaries with older glibc headers, so you can't use CET 
markup to determine the size of the stack allocation anyway.

Thanks,
Florian