Re: [PATCH 1/2] Linux/x86: Update cancel_jmp_buf to match __jmp_buf_tag [BZ #22563]

[Joseph Myers <joseph at codesourcery dot com>]

On Thu, 7 Dec 2017, H.J. Lu wrote:

> On x86, padding in struct __jmp_buf_tag is used for shadow stack pointer
> to support shadow stack in Intel Control-flow Enforcemen Technology.
> Since the cancel_jmp_buf array is passed to setjmp and longjmp by
> casting it to pointer to struct __jmp_buf_tag, it should be as large
> as struct __jmp_buf_tag.  This patch adds pthread.h, pthreaddef.h and
> pthreadP.h for Linux/x86 to define a new cancel_jmp_buf to match
> struct __jmp_buf_tag.

Duplicating the installed pthread.h is a bad idea (in general, we should 
avoid having architecture-specific variants of installed headers as much 
as possible, and, especially, define APIs in architecture-independent 
headers and limit architecture-specific variants to as few constants or 
structures as possible, those going in bits/ headers that at least people 
expect to have multiple variants).

Thus, we should aim to eliminate the hppa-specific variant of pthread.h by 
creating a bits/ header that has the minimum information required to 
encapsulate the hppa variations (or putting such information in an 
existing bits/ header, if appropriate), and likewise for whatever the 
differences are in your x86 variant.  We should certainly not create a new 
x86 variant of the whole of pthread.h.

-- 
Joseph S. Myers
joseph@codesourcery.com