This tiny program:

#define _GNU_SOURCE
#include <signal.h>
#include <asm/sigcontext.h>

fails to compile with many errors like this:

In file included from test_ucontext.c:5:
/usr/include/asm/sigcontext.h:40:8: error: redefinition of ‘struct _fpx_sw_bytes’
   40 | struct _fpx_sw_bytes {
      |        ^~~~~~~~~~~~~
In file included from /usr/include/signal.h:291,
                 from test_ucontext.c:2:
/usr/include/bits/sigcontext.h:31:8: note: originally defined here
   31 | struct _fpx_sw_bytes
      |        ^~~~~~~~~~~~~

Glibc's bits/sycontext.h is very similar to the kernel's asm/sigcontext.h, except that glibc's is a bit out of date and uses "__glibc_reserved1" instead of "padding".

Could glibc be switched to use sigcontext.h from the kernel headers?  This awful hack does indeed compile:

#define _GNU_SOURCE
#define _BITS_SIGCONTEXT_H 1
#include <asm/sigcontext.h>
#include <signal.h>

NB: this is a bit related to PR 21457 and, in particular, to commit  251287734e89.  The latter made <asm/ucontext.h> start working.