aarch64: Add SME runtime support

The runtime support routines for the call ABI of the Scalable Matrix
Extension (SME) are mostly in libgcc. Since libc.so cannot depend on
libgcc_s.so have an implementation of __arm_za_disable in libc for
libc internal use in longjmp and similar APIs.

__libc_arm_za_disable follows the same PCS rules as __arm_za_disable,
but it's a hidden symbol so it does not need variant PCS marking.

Using __libc_fatal instead of abort because it can print a message and
works in ld.so too. But for now we don't need SME routines in ld.so.

To check the SME HWCAP in asm, we need the _dl_hwcap2 member offset in
_rtld_global_ro in the shared libc.so, while in libc.a the _dl_hwcap2
object is accessed.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

sysdeps/aarch64/Makefile

@@ -48,7 +48,9 @@ endif
 endif
 
 ifeq ($(subdir),csu)
-gen-as-const-headers += tlsdesc.sym
+gen-as-const-headers += \
+  tlsdesc.sym \
+  rtld-global-offsets.sym
 endif
 
 ifeq ($(subdir),gmon)
@@ -62,8 +64,10 @@ endif
 
 ifeq ($(subdir),misc)
 sysdep_headers += sys/ifunc.h
-sysdep_routines += __mtag_tag_zero_region \
-		   __mtag_tag_region
+sysdep_routines += \
+  __mtag_tag_zero_region \
+  __mtag_tag_region \
+  __arm_za_disable
 endif
 
 ifeq ($(subdir),malloc)

sysdeps/aarch64/__arm_za_disable.S

@@ -0,0 +1,112 @@
+/* Libc internal support routine for SME.
+   Copyright (C) 2023 Free Software Foundation, Inc.
+
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library.  If not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <sysdep.h>
+#include <rtld-global-offsets.h>
+
+#define HWCAP2_SME_BIT 23
+
+/* Disable ZA.  Call ABI:
+   - Private ZA, streaming-compatible.
+   - x0-x13, x19-x29, sp and fp regs are call preserved.
+   - On return tpidr2_el0 = 0, ZA = 0.
+   - Takes no argument.
+   - Does not return a value.
+   - Can abort on failure (then registers are not preserved).  */
+
+ENTRY (__libc_arm_za_disable)
+
+	/* Check if SME is available.  */
+#ifdef SHARED
+	/* In libc.so.  */
+	adrp	x14, :got:_rtld_global_ro
+	ldr	x14, [x14, :got_lo12:_rtld_global_ro]
+	ldr	x14, [x14, GLRO_DL_HWCAP2_OFFSET]
+#else
+	/* In libc.a, may be PIC.  */
+	adrp	x14, _dl_hwcap2
+	ldr	x14, [x14, :lo12:_dl_hwcap2]
+#endif
+	tbz	x14, HWCAP2_SME_BIT, L(end)
+
+	.inst	0xd53bd0ae  /* mrs	x14, tpidr2_el0  */
+	cbz	x14, L(end)
+
+	/* Check reserved bytes, abort on unknown extensions.  */
+	ldrh	w15, [x14, 10]
+	ldr	w16, [x14, 12]
+	orr	w15, w15, w16
+	cbnz	w15, L(fail)
+
+	ldr	x16, [x14]
+	cbz	x16, L(end)
+	ldrh	w17, [x14, 8]
+	cbz	w17, L(end)
+
+	/* x14: tpidr2, x15: 0,
+	   x16: za_save_buffer, x17: num_za_save_slices.  */
+
+L(save_loop):
+	.inst	0xe1206200  /* str	za[w15, 0], [x16]  */
+	.inst	0xe1206201  /* str	za[w15, 1], [x16, 1, mul vl] */
+	.inst	0xe1206202  /* str	za[w15, 2], [x16, 2, mul vl] */
+	.inst	0xe1206203  /* str	za[w15, 3], [x16, 3, mul vl] */
+	.inst	0xe1206204  /* str	za[w15, 4], [x16, 4, mul vl] */
+	.inst	0xe1206205  /* str	za[w15, 5], [x16, 5, mul vl] */
+	.inst	0xe1206206  /* str	za[w15, 6], [x16, 6, mul vl] */
+	.inst	0xe1206207  /* str	za[w15, 7], [x16, 7, mul vl] */
+	.inst	0xe1206208  /* str	za[w15, 8], [x16, 8, mul vl] */
+	.inst	0xe1206209  /* str	za[w15, 9], [x16, 9, mul vl] */
+	.inst	0xe120620a  /* str	za[w15, 10], [x16, 10, mul vl] */
+	.inst	0xe120620b  /* str	za[w15, 11], [x16, 11, mul vl] */
+	.inst	0xe120620c  /* str	za[w15, 12], [x16, 12, mul vl] */
+	.inst	0xe120620d  /* str	za[w15, 13], [x16, 13, mul vl] */
+	.inst	0xe120620e  /* str	za[w15, 14], [x16, 14, mul vl] */
+	.inst	0xe120620f  /* str	za[w15, 15], [x16, 15, mul vl] */
+	add	w15, w15, 16
+	.inst	0x04305a10  /* addsvl	x16, x16, 16  */
+	cmp	w17, w15
+	bhi	L(save_loop)
+	.inst	0xd51bd0bf  /* msr	tpidr2_el0, xzr  */
+	.inst	0xd503447f  /* smstop	za  */
+L(end):
+	ret
+L(fail):
+#if HAVE_AARCH64_PAC_RET
+	PACIASP
+	cfi_window_save
+#endif
+	stp	x29, x30, [sp, -32]!
+	cfi_adjust_cfa_offset (32)
+	cfi_rel_offset (x29, 0)
+	cfi_rel_offset (x30, 8)
+	mov	x29, sp
+	.inst	0x04e0e3f0  /* cntd	x16  */
+	str	x16, [sp, 16]
+	cfi_rel_offset (46, 16)
+	.inst	0xd503467f  /* smstop  */
+	adrp	x0, L(msg)
+	add	x0, x0, :lo12:L(msg)
+	bl	HIDDEN_JUMPTARGET (__libc_fatal)
+END (__libc_arm_za_disable)
+
+	.section        .rodata
+	.align  3
+L(msg):
+	.string "FATAL: __libc_arm_za_disable failed.\n"

sysdeps/aarch64/rtld-global-offsets.sym

@@ -0,0 +1,10 @@
+#define SHARED 1
+
+#include <ldsodefs.h>
+
+#define GLRO_offsetof(name) offsetof (struct rtld_global_ro, _##name)
+
+-- Offsets of _rtld_global_ro in libc.so
+
+GLRO_DL_HWCAP_OFFSET	GLRO_offsetof (dl_hwcap)
+GLRO_DL_HWCAP2_OFFSET	GLRO_offsetof (dl_hwcap2)