base/dispatch.c, rand/rand.c, and asm: Support `rdseed' for quick noise.

[catacomb] / base / dispatch-x86ish.S

/// -*- mode: asm; asm-comment-char: ?/ -*-
///
/// CPU dispatch support for x86
///
/// (c) 2019 Straylight/Edgeware
///

///----- Licensing notice ---------------------------------------------------
///
/// This file is part of Catacomb.
///
/// Catacomb is free software: you can redistribute it and/or modify it
/// under the terms of the GNU Library General Public License as published
/// by the Free Software Foundation; either version 2 of the License, or
/// (at your option) any later version.
///
/// Catacomb is distributed in the hope that it will be useful, but
/// WITHOUT ANY WARRANTY; without even the implied warranty of
/// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
/// Library General Public License for more details.
///
/// You should have received a copy of the GNU Library General Public
/// License along with Catacomb.  If not, write to the Free Software
/// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
/// USA.

///--------------------------------------------------------------------------
/// Preliminaries.

#include "config.h"
#include "asm-common.h"

	EFLAGS_ID = 1 << 21

	.text

///--------------------------------------------------------------------------
/// Probing for CPUID.

FUNC(dispatch_x86ish_cpuid)
	// Enter with a pointer to 16 bytes of storage for the output A, B,
	// C, D values in the first argument, and input A and C values in the
	// second and third.  Fill the output buffer with `cpuid' results and
	// return zero if we can; otherwise fill with zero and return -1.

#if CPUFAM_X86
	pushreg	ebx
	pushreg	edi
	mov	edi, [SP + 12]
	mov	eax, [SP + 16]
	mov	ecx, [SP + 20]
#  define OUT edi
#endif
#if CPUFAM_AMD64 && ABI_SYSV
	pushreg	rbx
	mov	eax, esi
	mov	ecx, edx
#  define OUT rdi
#endif
#if CPUFAM_AMD64 && ABI_WIN
	pushreg	rbx
	mov	r9, rcx
	mov	eax, edx
	mov	ecx, r8d
#  define OUT r9
#endif
  endprologue

	// First, check that this is even a thing, using the complicated
	// dance with the flags register.
	pushf
	pop	DX			// current flags in d

	or	DX, EFLAGS_ID		// force the id bit on and check it
	push	DX
	popf
	pushf
	pop	DX
	test	edx, EFLAGS_ID
	jz	8f

	and	DX, ~EFLAGS_ID		// force the id bit off and check it
	push	DX
	popf
	pushf
	pop	DX
	test	edx, EFLAGS_ID
	jnz	8f

	// OK, that seemed to work.
	cpuid

	mov	[OUT + 0], eax
	mov	[OUT + 4], ebx
	mov	[OUT + 8], ecx
	mov	[OUT + 12], edx
	xor	eax, eax

	// We're done.
9:
#if CPUFAM_X86
	popreg	edi
	popreg	ebx
#endif
#if CPUFAM_AMD64
	popreg	rbx
#endif
	ret

	// Failed.
8:	xor	eax, eax
	mov	[OUT + 0], eax
	mov	[OUT + 4], eax
	mov	[OUT + 8], eax
	mov	[OUT + 12], eax
	mov	eax, -1
	jmp	9b
ENDFUNC

///--------------------------------------------------------------------------
/// Probing for XMM register availability.

FUNC(dispatch_x86ish_xmmregisters_p)
	// Enter with no arguments.  Return nonzero if the XMM registers are
	// usable.

	pushreg	BP
	setfp
	stalloc	512
	and	SP, ~15
  endprologue

	// Save the floating point and SIMD registers, and try to clobber
	// xmm0.
	lea	DX, [SP + 160]
	fxsave	[SP]
	mov	eax, [DX]
	xor	dword ptr [DX], 0xaaaa5555
	fxrstor	[SP]

	// Save them again, and read back the low word of xmm0.  Undo the
	// clobbering and restore.
	fxsave	[SP]
	mov	ecx, [DX]
	mov	[DX], eax
	fxrstor	[SP]

	// The register are live if we read different things.
	xor	eax, ecx

	// Done.
	dropfp
	popreg	BP
	ret
ENDFUNC

///--------------------------------------------------------------------------
/// Checking `rdrand'.

FUNC(dispatch_x86ish_rdrand)
	// Enter with two arguments: a code OP requesting either `rdrand' (0)
	// or `rdseed' (1), and a pointer X_OUT to a 32-bit word.  Try to
	// generate a random word using the requested instruction'.  If
	// successful, set *X_OUT to the generated word, and return zero;
	// otherwise, return -1.

#if CPUFAM_X86
#  define OP eax
#  define X_OUT edx
#  define COUNT ecx
	mov	OP, [SP + 4]
	mov	X_OUT, [SP + 8]
#endif
#if CPUFAM_AMD64 && ABI_SYSV
#  define OP edi
#  define X_OUT rsi
#  define COUNT ecx
#endif
#if CPUFAM_AMD64 && ABI_WIN
#  define OP rcx
#  define X_OUT rdx
#  define COUNT r8d
#endif
  endprologue

	cmp	OP, 0
	mov	COUNT, 16		// fairly persistent
	jne	1f

0:	rdrand	eax
	jc	9f
	dec	COUNT
	jnz	0b
	jmp	8f

1:	rdseed	eax
	jc	9f
	dec	COUNT
	jnz	1b
	jmp	8f

	// Failed to come up with a random value.
8:	mov	eax, -1
	ret

	// Success.
9:	mov	[X_OUT], eax
	xor	eax, eax
	ret

#undef X_OUT
#undef COUNT

ENDFUNC

///----- That's all, folks --------------------------------------------------