[uml-devel] [PATCH v2 0/3] um: Add support for extended processor state

[Eli Cooper <elicooper@gmx.com>]

This series adds support for the extended processor state (XSTATE) for
x86_64 UML, especially the YMM registers used by AVX/AVX2 instructions.

Modern userspace programs built with AVX can now run inside x86_64 UML
without YMM registers getting corrupted.

Tested with a tiny selftest program below, which of course requires the
following patch I sent earlier today to run correctly.
  um: fix FPU register double-restore after sigreturn

Also tested with a latest Arch Linux image on a CPU with AVX2 support.
Without YMM support in UML, a lot of programs crash unexpectedly,
or result in bad results (e.g., calculating SHA256 in OpenSSL).


Changes since v1:
 - Refactor functions with oversized stack frame
 - Add a tiny selftest program to the cover letter

Eli Cooper (3):
  um: extend _fpstate to _xstate
  um: add extended processor state save/restore support
  um: fix ptrace PTRACE_GETFPREGS and PTRACE_SETFPREG support

 arch/um/include/shared/registers.h    |  2 ++
 arch/um/kernel/process.c              |  2 +-
 arch/um/os-Linux/signal.c             | 28 ++++++++++++-----
 arch/x86/um/os-Linux/registers.c      | 49 ++++++++++++++++++++++++++++--
 arch/x86/um/ptrace_32.c               |  5 +--
 arch/x86/um/ptrace_64.c               | 16 +++++-----
 arch/x86/um/shared/sysdep/ptrace_64.h |  4 +--
 arch/x86/um/signal.c                  | 57 +++++++++++++++++++++++------------
 arch/x86/um/user-offsets.c            |  2 +-
 9 files changed, 121 insertions(+), 44 deletions(-)

---
/* test if context switches preserve YMM registers, should exit with code 0 */
#include <stdint.h>
#include <unistd.h>
#include <signal.h>
#include <immintrin.h>

int flag;
void sighandler(int signum)
{
	if (flag)
		exit(0);
	alarm(1);
	flag = 1;
	__m256i m0 = _mm256_set_epi64x(0, 0, 0, 0);
}

int main()
{
	register uint32_t a asm("eax") = 0;
	signal(SIGALRM, sighandler);
	alarm(1);

	__m256i m0 = _mm256_set_epi64x(1L << 32, 0, 0, 0);
	do {
		asm("vextracti128 $1,%ymm0,%xmm1");
		asm("vpextrd $3,%xmm1,%eax");
	} while (a == 1);

	return 1;
}


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