gdb: change regcache interface to use array_view

Change most of regcache (and base classes) to use array_view when
possible, instead of raw pointers.  By propagating the use of array_view
further, it enables having some runtime checks to make sure the what we
read from or write to regcaches has the expected length (such as the one
in the `copy(array_view, array_view)` function.  It also integrates well
when connecting with other APIs already using gdb::array_view.

Add some overloads of the methods using raw pointers to avoid having to
change all call sites at once (which is both a lot of work and risky).

I tried to do this change in small increments, but since many of these
functions use each other, it ended up simpler to do it in one shot than
having a lot of intermediary / transient changes.

This change extends into gdbserver as well, because there is some part
of the regcache interface that is shared.

Changing the reg_buffer_common interface to use array_view caused some
build failures in nat/aarch64-scalable-linux-ptrace.c.  That file
currently "takes advantage" of the fact that
reg_buffer_common::{raw_supply,raw_collect} operates on `void *`, which
IMO is dangerous.  It uses raw_supply/raw_collect directly on
uint64_t's, which I guess is fine because it is expected that native
code will have the same endianness as the debugged process.  To
accomodate that, add some overloads of raw_collect and raw_supply that
work on uint64_t.

This file also uses raw_collect and raw_supply on `char` pointers.
Change it to use `gdb_byte` pointers instead.  Add overloads of
raw_collect and raw_supply that work on `gdb_byte *` and make an
array_view on the fly using the register's size.  Those call sites could
be converted to use array_view with not much work, in which case these
overloads could be removed, but I didn't want to do it in this patch, to
avoid starting to dig in arch-specific code.

During development, I inadvertently changed reg_buffer::raw_compare's
behavior to not accept an offset equal to the register size.  This
behavior (effectively comparing 0 bytes, returning true) change was
caught by the AArch64 SME core tests.  Add a selftest to make sure that
this raw_compare behavior is preserved in the future.

Change-Id: I9005f04114543ddff738949e12d85a31855304c2
Reviewed-By: John Baldwin <jhb@FreeBSD.org>

2 files changed, 30 insertions, 23 deletions

diff --git a/gdbserver/regcache.cc b/gdbserver/regcache.cc
index 823ea1f..c5d3670 100644
--- a/gdbserver/regcache.cc
+++ b/gdbserver/regcache.cc
@@ -315,27 +315,32 @@ regcache_register_size (const reg_buffer_common *regcache, int n)
     (gdb::checked_static_cast<const struct regcache *> (regcache)->tdesc, n);
 }
 
-static unsigned char *
+static gdb::array_view<gdb_byte>
 register_data (const struct regcache *regcache, int n)
 {
-  return (regcache->registers
-	  + find_register_by_number (regcache->tdesc, n).offset / 8);
+  const gdb::reg &reg = find_register_by_number (regcache->tdesc, n);
+  return gdb::make_array_view (regcache->registers + reg.offset / 8,
+			       reg.size / 8);
 }
 
 void
-supply_register (struct regcache *regcache, int n, const void *buf)
+supply_register (struct regcache *regcache, int n, const void *vbuf)
 {
-  return regcache->raw_supply (n, buf);
+  const gdb::reg &reg = find_register_by_number (regcache->tdesc, n);
+  const gdb_byte *buf = static_cast<const gdb_byte *> (vbuf);
+  return regcache->raw_supply (n, gdb::make_array_view (buf, reg.size / 8));
 }
 
 /* See gdbsupport/common-regcache.h.  */
 
 void
-regcache::raw_supply (int n, const void *buf)
+regcache::raw_supply (int n, gdb::array_view<const gdb_byte> src)
 {
-  if (buf)
+  auto dst = register_data (this, n);
+
+  if (src.data () != nullptr)
     {
-      memcpy (register_data (this, n), buf, register_size (tdesc, n));
+      copy (src, dst);
 #ifndef IN_PROCESS_AGENT
       if (register_status != NULL)
 	register_status[n] = REG_VALID;
@@ -343,7 +348,7 @@ regcache::raw_supply (int n, const void *buf)
     }
   else
     {
-      memset (register_data (this, n), 0, register_size (tdesc, n));
+      memset (dst.data (), 0, dst.size ());
 #ifndef IN_PROCESS_AGENT
       if (register_status != NULL)
 	register_status[n] = REG_UNAVAILABLE;
@@ -356,8 +361,8 @@ regcache::raw_supply (int n, const void *buf)
 void
 supply_register_zeroed (struct regcache *regcache, int n)
 {
-  memset (register_data (regcache, n), 0,
-	  register_size (regcache->tdesc, n));
+  auto dst = register_data (regcache, n);
+  memset (dst.data (), 0, dst.size ());
 #ifndef IN_PROCESS_AGENT
   if (regcache->register_status != NULL)
     regcache->register_status[n] = REG_VALID;
@@ -426,17 +431,20 @@ supply_register_by_name (struct regcache *regcache,
 #endif
 
 void
-collect_register (struct regcache *regcache, int n, void *buf)
+collect_register (struct regcache *regcache, int n, void *vbuf)
 {
-  regcache->raw_collect (n, buf);
+  const gdb::reg &reg = find_register_by_number (regcache->tdesc, n);
+  gdb_byte *buf = static_cast<gdb_byte *> (vbuf);
+  regcache->raw_collect (n, gdb::make_array_view (buf, reg.size / 8));
 }
 
 /* See gdbsupport/common-regcache.h.  */
 
 void
-regcache::raw_collect (int n, void *buf) const
+regcache::raw_collect (int n, gdb::array_view<gdb_byte> dst) const
 {
-  memcpy (buf, register_data (this, n), register_size (tdesc, n));
+  auto src = register_data (this, n);
+  copy (src, dst);
 }
 
 enum register_status
@@ -476,8 +484,7 @@ regcache_raw_get_unsigned_by_name (struct regcache *regcache,
 void
 collect_register_as_string (struct regcache *regcache, int n, char *buf)
 {
-  bin2hex (register_data (regcache, n), buf,
-	   register_size (regcache->tdesc, n));
+  bin2hex (register_data (regcache, n), buf);
 }
 
 void
@@ -524,9 +531,9 @@ regcache::raw_compare (int regnum, const void *buf, int offset) const
 {
   gdb_assert (buf != NULL);
 
-  const unsigned char *regbuf = register_data (this, regnum);
-  int size = register_size (tdesc, regnum);
-  gdb_assert (size >= offset);
+  gdb::array_view<const gdb_byte> regbuf = register_data (this, regnum);
+  gdb_assert (offset < regbuf.size ());
+  regbuf = regbuf.slice (offset);
 
-  return (memcmp (buf, regbuf + offset, size - offset) == 0);
+  return memcmp (buf, regbuf.data (), regbuf.size ()) == 0;
 }
diff --git a/gdbserver/regcache.h b/gdbserver/regcache.h
index 4700c03..02791a0 100644
--- a/gdbserver/regcache.h
+++ b/gdbserver/regcache.h
@@ -50,10 +50,10 @@ struct regcache : public reg_buffer_common
   enum register_status get_register_status (int regnum) const override;
 
   /* See gdbsupport/common-regcache.h.  */
-  void raw_supply (int regnum, const void *buf) override;
+  void raw_supply (int regnum, gdb::array_view<const gdb_byte> src) override;
 
   /* See gdbsupport/common-regcache.h.  */
-  void raw_collect (int regnum, void *buf) const override;
+  void raw_collect (int regnum, gdb::array_view<gdb_byte> dst) const override;
 
   /* See gdbsupport/common-regcache.h.  */
   bool raw_compare (int regnum, const void *buf, int offset) const override;