[PATCH 2/8] Function for reading the Aarch64 SVE vector length.

[Alan Hayward <alan.hayward@arm.com>]

Add a method for reading the SVE vector length using ptrace. This returns
0 for systems without SVE support.

Note the defines taken from Linux kernel headers in aarch64-sve-linux-ptrace.h.
See the covering email for details about this.

There are multiple ways of expressing the vector length. Thankfully these are
all wll defined. I've added convertors for going from one to the other.
Hopefully this will help to prevent future confusion.

2018-05-11  Alan Hayward  <alan.hayward@arm.com>

gdb/
	* Makefile.in: Add new header.
	* gdb/arch/aarch64.h (sve_vg_from_vl): New macro.
	(sve_vl_from_vg): Likewise.
	(sve_vq_from_vl): Likewise.
	(sve_vl_from_vq): Likewise.
	(sve_vq_from_vg): Likewise.
	(sve_vg_from_vq): Likewise.
	* configure.nat: Add new c file.
	* nat/aarch64-sve-linux-ptrace.c: New file.
	* nat/aarch64-sve-linux-ptrace.h: New file.

gdbserver/
	* configure.srv: Add new c/h file.
---
 gdb/Makefile.in                    |  1 +
 gdb/arch/aarch64.h                 | 17 +++++++++
 gdb/configure.nat                  |  2 +-
 gdb/gdbserver/configure.srv        |  1 +
 gdb/nat/aarch64-sve-linux-ptrace.c | 52 +++++++++++++++++++++++++++
 gdb/nat/aarch64-sve-linux-ptrace.h | 73 ++++++++++++++++++++++++++++++++++++++
 6 files changed, 145 insertions(+), 1 deletion(-)
 create mode 100644 gdb/nat/aarch64-sve-linux-ptrace.c
 create mode 100644 gdb/nat/aarch64-sve-linux-ptrace.h

diff --git a/gdb/Makefile.in b/gdb/Makefile.in
index 87d74a7703..64042d1bd1 100644
--- a/gdb/Makefile.in
+++ b/gdb/Makefile.in
@@ -1478,6 +1478,7 @@ HFILES_NO_SRCDIR = \
 	mi/mi-parse.h \
 	nat/aarch64-linux.h \
 	nat/aarch64-linux-hw-point.h \
+	nat/aarch64-sve-linux-ptrace.h \
 	nat/amd64-linux-siginfo.h \
 	nat/gdb_ptrace.h \
 	nat/gdb_thread_db.h \
diff --git a/gdb/arch/aarch64.h b/gdb/arch/aarch64.h
index 1846e04163..af0b157c51 100644
--- a/gdb/arch/aarch64.h
+++ b/gdb/arch/aarch64.h
@@ -48,6 +48,23 @@ enum aarch64_regnum
 #define AARCH64_V_REGS_NUM 32
 #define AARCH64_NUM_REGS AARCH64_FPCR_REGNUM + 1
 
+/* There are a number of ways of expressing the current SVE vector size:
+
+   VL : Vector Length.
+	The number of bytes in an SVE Z register.
+   VQ : Vector Quotient.
+	The number of 128bit chunks in an SVE Z register.
+   VG : Vector Gradient.
+	The number of 64bit chunks in an SVE Z register.  */
+
+#define sve_vg_from_vl(vl)	((vl) / 8)
+#define sve_vl_from_vg(vg)	((vg) * 8)
+#define sve_vq_from_vl(vl)	((vl) / 0x10)
+#define sve_vl_from_vq(vq)	((vq) * 0x10)
+#define sve_vq_from_vg(vg)	(sve_vq_from_vl (sve_vl_from_vg (vg)))
+#define sve_vg_from_vq(vq)	(sve_vg_from_vl (sve_vl_from_vq (vq)))
+
+
 /* Maximum supported VQ value.  Increase if required.  */
 #define AARCH64_MAX_SVE_VQ  16
 
diff --git a/gdb/configure.nat b/gdb/configure.nat
index 6b0f44fede..d7d79adaca 100644
--- a/gdb/configure.nat
+++ b/gdb/configure.nat
@@ -228,7 +228,7 @@ case ${gdb_host} in
 	    aarch64)
 		#  Host: AArch64 based machine running GNU/Linux
 		NATDEPFILES="${NATDEPFILES} aarch64-linux-nat.o \
-		aarch32-linux-nat.o aarch64-linux-hw-point.o aarch64-linux.o"
+		aarch32-linux-nat.o aarch64-linux-hw-point.o aarch64-linux.o aarch64-sve-linux-ptrace.o"
 		;;
 	    arm)
 		# Host: ARM based machine running GNU/Linux
diff --git a/gdb/gdbserver/configure.srv b/gdb/gdbserver/configure.srv
index ffeefb9b92..8bf0dcc650 100644
--- a/gdb/gdbserver/configure.srv
+++ b/gdb/gdbserver/configure.srv
@@ -54,6 +54,7 @@ case "${target}" in
 			srv_tgtobj="$srv_tgtobj arch/aarch64-insn.o"
 			srv_tgtobj="$srv_tgtobj arch/aarch64.o"
 			srv_tgtobj="$srv_tgtobj linux-aarch64-tdesc.o"
+			srv_tgtobj="$srv_tgtobj aarch64-sve-linux-ptrace.o"
 			srv_tgtobj="${srv_tgtobj} $srv_linux_obj"
 			srv_linux_regsets=yes
 			srv_linux_thread_db=yes
diff --git a/gdb/nat/aarch64-sve-linux-ptrace.c b/gdb/nat/aarch64-sve-linux-ptrace.c
new file mode 100644
index 0000000000..9381786fda
--- /dev/null
+++ b/gdb/nat/aarch64-sve-linux-ptrace.c
@@ -0,0 +1,52 @@
+/* Common target dependent for AArch64 systems.
+
+   Copyright (C) 2017 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program 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 General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <sys/utsname.h>
+#include <sys/uio.h>
+#include "common-defs.h"
+#include "elf/external.h"
+#include "elf/common.h"
+#include "aarch64-sve-linux-ptrace.h"
+#include "arch/aarch64.h"
+
+/* Read VQ for the given tid using ptrace.  If SVE is not supported then zero
+   is returned (on a system that supports SVE, then VQ cannot be zeo).  */
+
+unsigned long
+aarch64_sve_get_vq (int tid)
+{
+  struct iovec iovec;
+  struct user_sve_header header;
+
+  iovec.iov_len = sizeof (header);
+  iovec.iov_base = &header;
+
+  /* Ptrace gives the vector length in bytes.  Convert it to VQ, the number of
+     128bit chunks in a Z register.  We use VQ because 128bits is the minimum
+     a Z register can increase in size.  */
+
+  if (ptrace (PTRACE_GETREGSET, tid, NT_ARM_SVE, &iovec) < 0)
+    /* SVE is not supported.  */
+    return 0;
+
+  long vq = sve_vq_from_vl (header.vl);
+  gdb_assert (sve_vl_valid (header.vl));
+
+  return vq;
+}
diff --git a/gdb/nat/aarch64-sve-linux-ptrace.h b/gdb/nat/aarch64-sve-linux-ptrace.h
new file mode 100644
index 0000000000..b318150ac1
--- /dev/null
+++ b/gdb/nat/aarch64-sve-linux-ptrace.h
@@ -0,0 +1,73 @@
+/* Common target dependent for AArch64 systems.
+
+   Copyright (C) 2017 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program 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 General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#ifndef AARCH64_SVE_LINUX_PTRACE_H
+#define AARCH64_SVE_LINUX_PTRACE_H
+
+/* Where indicated, this file contains defines and macros lifted directly from
+   the Linux kernel headers, with no modification.
+   Refer to Linux kernel documentation for details.  */
+
+#include <asm/sigcontext.h>
+#include <sys/utsname.h>
+#include <sys/ptrace.h>
+#include <asm/ptrace.h>
+
+/* Read VQ for the given tid using ptrace.  If SVE is not supported then zero
+   is returned (on a system that supports SVE, then VQ cannot be zeo).  */
+
+extern unsigned long aarch64_sve_get_vq (int tid);
+
+/* Structures and defines taken from sigcontext.h.  */
+
+#ifndef SVE_SIG_ZREGS_SIZE
+
+#define SVE_VQ_BYTES		16	/* number of bytes per quadword */
+
+#define SVE_VQ_MIN		1
+#define SVE_VQ_MAX		512
+
+#define SVE_VL_MIN		(SVE_VQ_MIN * SVE_VQ_BYTES)
+#define SVE_VL_MAX		(SVE_VQ_MAX * SVE_VQ_BYTES)
+
+#define SVE_NUM_ZREGS		32
+#define SVE_NUM_PREGS		16
+
+#define sve_vl_valid(vl) \
+	((vl) % SVE_VQ_BYTES == 0 && (vl) >= SVE_VL_MIN && (vl) <= SVE_VL_MAX)
+
+#endif /* SVE_SIG_ZREGS_SIZE.  */
+
+
+/* Structures and defines taken from ptrace.h.  */
+
+#ifndef SVE_PT_SVE_ZREG_SIZE
+
+struct user_sve_header {
+	__u32 size; /* total meaningful regset content in bytes */
+	__u32 max_size; /* maxmium possible size for this thread */
+	__u16 vl; /* current vector length */
+	__u16 max_vl; /* maximum possible vector length */
+	__u16 flags;
+	__u16 __reserved;
+};
+
+#endif /* SVE_PT_SVE_ZREG_SIZE.  */
+
+#endif /* aarch64-sve-linux-ptrace.h */
-- 
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