gdb/gdbserver: share x86/linux tdesc caching

This commit builds on the previous series of commits to share the
target description caching code between GDB and gdbserver for
x86/Linux targets.

The objective of this commit is to move the four functions (2 each of)
i386_linux_read_description and amd64_linux_read_description into
gdb/nat/x86-linux-tdesc.c and combine them so we have just a single
copy of each.  Then both GDB and gdbserver will link against these
shared functions.

It is worth reading the description of the previous commit to see why
this merging is not as simple as it seems: on the gdbserver side we
actually have two users of these functions, gdbserver itself, and the
in process agent (IPA).

However, the previous commit streamlined the gdbserver code, and so
now it is simple to move the two functions along with all their
support functions from the gdbserver directory into the gdb/nat/
directory, and then GDB is fine to call these functions.

One small curiosity with this patch is the function
x86_linux_post_init_tdesc.  On the gdbserver side the two functions
amd64_linux_read_description and i386_linux_read_description have some
functionality that is not present on the GDB side, that is some
additional configuration that is performed as each target description
is created to setup the expedited registers.

To support this I've added the function x86_linux_post_init_tdesc.
This function is called from the two *_linux_read_description
functions, but is implemented separately for GDB and gdbserver.

This does mean adding back some non-shared code when this whole series
has been about sharing code, but now the only non-shared bit is the
single line that is actually different between GDB and gdbserver, all
the rest, which is identical, is now shared.

I did need to add a new rule to the gdbserver Makefile, this is to
allow the nat/x86-linux-tdesc.c file to be compiled for the IPA.

Approved-By: John Baldwin <jhb@FreeBSD.org>

4 files changed, 343 insertions, 61 deletions

diff --git a/gdb/amd64-linux-tdep.c b/gdb/amd64-linux-tdep.c
index 7e0900d..e149034 100644
--- a/gdb/amd64-linux-tdep.c
+++ b/gdb/amd64-linux-tdep.c
@@ -1579,37 +1579,6 @@ amd64_linux_record_signal (struct gdbarch *gdbarch,
   return 0;
 }
 
-const target_desc *
-amd64_linux_read_description (uint64_t xcr0_features_bit, bool is_x32)
-{
-  static target_desc *amd64_linux_tdescs \
-    [2/*AVX*/][2/*MPX*/][2/*AVX512*/][2/*PKRU*/] = {};
-  static target_desc *x32_linux_tdescs \
-    [2/*AVX*/][2/*AVX512*/][2/*PKRU*/] = {};
-
-  target_desc **tdesc;
-
-  if (is_x32)
-    {
-      tdesc = &x32_linux_tdescs[(xcr0_features_bit & X86_XSTATE_AVX) ? 1 : 0 ]
-	[(xcr0_features_bit & X86_XSTATE_AVX512) ? 1 : 0]
-	[(xcr0_features_bit & X86_XSTATE_PKRU) ? 1 : 0];
-    }
-  else
-    {
-      tdesc = &amd64_linux_tdescs[(xcr0_features_bit & X86_XSTATE_AVX) ? 1 : 0]
-	[(xcr0_features_bit & X86_XSTATE_MPX) ? 1 : 0]
-	[(xcr0_features_bit & X86_XSTATE_AVX512) ? 1 : 0]
-	[(xcr0_features_bit & X86_XSTATE_PKRU) ? 1 : 0];
-    }
-
-  if (*tdesc == NULL)
-    *tdesc = amd64_create_target_description (xcr0_features_bit, is_x32,
-					      true, true);
-
-  return *tdesc;
-}
-
 /* Get Linux/x86 target description from core dump.  */
 
 static const struct target_desc *
diff --git a/gdb/i386-linux-tdep.c b/gdb/i386-linux-tdep.c
index f5f7a36..ed14422 100644
--- a/gdb/i386-linux-tdep.c
+++ b/gdb/i386-linux-tdep.c
@@ -681,29 +681,12 @@ i386_linux_core_read_x86_xsave_layout (struct gdbarch *gdbarch,
 					  layout) != 0;
 }
 
-/* See i386-linux-tdep.h.  */
+/* See nat/x86-linux-tdesc.h.  */
 
-const struct target_desc *
-i386_linux_read_description (uint64_t xcr0)
+void
+x86_linux_post_init_tdesc (target_desc *tdesc, bool is_64bit)
 {
-  if (xcr0 == 0)
-    return NULL;
-
-  static struct target_desc *i386_linux_tdescs \
-    [2/*X87*/][2/*SSE*/][2/*AVX*/][2/*MPX*/][2/*AVX512*/][2/*PKRU*/] = {};
-  struct target_desc **tdesc;
-
-  tdesc = &i386_linux_tdescs[(xcr0 & X86_XSTATE_X87) ? 1 : 0]
-    [(xcr0 & X86_XSTATE_SSE) ? 1 : 0]
-    [(xcr0 & X86_XSTATE_AVX) ? 1 : 0]
-    [(xcr0 & X86_XSTATE_MPX) ? 1 : 0]
-    [(xcr0 & X86_XSTATE_AVX512) ? 1 : 0]
-    [(xcr0 & X86_XSTATE_PKRU) ? 1 : 0];
-
-  if (*tdesc == NULL)
-    *tdesc = i386_create_target_description (xcr0, true, false);
-
-  return *tdesc;
+  /* Nothing.  */
 }
 
 /* Get Linux/x86 target description from core dump.  */
@@ -716,7 +699,10 @@ i386_linux_core_read_description (struct gdbarch *gdbarch,
   /* Linux/i386.  */
   x86_xsave_layout layout;
   uint64_t xcr0 = i386_linux_core_read_xsave_info (abfd, layout);
-  const struct target_desc *tdesc = i386_linux_read_description (xcr0);
+
+  const struct target_desc *tdesc;
+  if (xcr0 != 0)
+    tdesc = i386_linux_read_description (xcr0);
 
   if (tdesc != NULL)
     return tdesc;
diff --git a/gdb/nat/x86-linux-tdesc.c b/gdb/nat/x86-linux-tdesc.c
index be7014d..c438dfa 100644
--- a/gdb/nat/x86-linux-tdesc.c
+++ b/gdb/nat/x86-linux-tdesc.c
@@ -38,6 +38,8 @@
 #include <sys/user.h>
 #include <sys/user.h>
 
+#ifndef IN_PROCESS_AGENT
+
 /* See nat/x86-linux-tdesc.h.  */
 
 const target_desc *
@@ -122,3 +124,288 @@ x86_linux_tdesc_for_tid (int tid, enum tribool *have_ptrace_getregset,
 
   gdb_assert_not_reached ("failed to return tdesc");
 }
+
+#endif /* !IN_PROCESS_AGENT */
+
+
+
+/* A structure used to describe a single cpu feature that might, or might
+   not, be checked for when creating a target description for one of i386,
+   amd64, or x32.  */
+
+struct x86_tdesc_feature {
+  /* The cpu feature mask.  This is a mask against an xcr0 value.  */
+  uint64_t feature;
+
+  /* Is this feature checked when creating an i386 target description.  */
+  bool is_i386;
+
+  /* Is this feature checked when creating an amd64 target description.  */
+  bool is_amd64;
+
+  /* Is this feature checked when creating an x32 target description.  */
+  bool is_x32;
+};
+
+/* A constant table that describes all of the cpu features that are
+   checked when building a target description for i386, amd64, or x32.  */
+
+static constexpr x86_tdesc_feature x86_linux_all_tdesc_features[] = {
+  /* Feature,           i386,	amd64,	x32.  */
+  { X86_XSTATE_PKRU,	true,	true, 	true },
+  { X86_XSTATE_AVX512,	true,	true, 	true },
+  { X86_XSTATE_AVX,	true,	true, 	true },
+  { X86_XSTATE_MPX,	true,	true, 	false },
+  { X86_XSTATE_SSE,	true,	false, 	false },
+  { X86_XSTATE_X87,	true,	false, 	false }
+};
+
+/* Return a compile time constant which is a mask of all the cpu features
+   that are checked for when building an i386 target description.  */
+
+static constexpr uint64_t
+x86_linux_i386_tdesc_feature_mask ()
+{
+  uint64_t mask = 0;
+
+  for (const auto &entry : x86_linux_all_tdesc_features)
+    if (entry.is_i386)
+      mask |= entry.feature;
+
+  return mask;
+}
+
+/* Return a compile time constant which is a mask of all the cpu features
+   that are checked for when building an amd64 target description.  */
+
+static constexpr uint64_t
+x86_linux_amd64_tdesc_feature_mask ()
+{
+  uint64_t mask = 0;
+
+  for (const auto &entry : x86_linux_all_tdesc_features)
+    if (entry.is_amd64)
+      mask |= entry.feature;
+
+  return mask;
+}
+
+/* Return a compile time constant which is a mask of all the cpu features
+   that are checked for when building an x32 target description.  */
+
+static constexpr uint64_t
+x86_linux_x32_tdesc_feature_mask ()
+{
+  uint64_t mask = 0;
+
+  for (const auto &entry : x86_linux_all_tdesc_features)
+    if (entry.is_x32)
+      mask |= entry.feature;
+
+  return mask;
+}
+
+/* Return a compile time constant which is a count of the number of cpu
+   features that are checked for when building an i386 target description.  */
+
+static constexpr int
+x86_linux_i386_tdesc_count ()
+{
+  uint64_t count = 0;
+
+  for (const auto &entry : x86_linux_all_tdesc_features)
+    if (entry.is_i386)
+      ++count;
+
+  gdb_assert (count > 0);
+
+  return (1 << count);
+}
+
+/* Return a compile time constant which is a count of the number of cpu
+   features that are checked for when building an amd64 target description.  */
+
+static constexpr int
+x86_linux_amd64_tdesc_count ()
+{
+  uint64_t count = 0;
+
+  for (const auto &entry : x86_linux_all_tdesc_features)
+    if (entry.is_amd64)
+      ++count;
+
+  gdb_assert (count > 0);
+
+  return (1 << count);
+}
+
+/* Return a compile time constant which is a count of the number of cpu
+   features that are checked for when building an x32 target description.  */
+
+static constexpr int
+x86_linux_x32_tdesc_count ()
+{
+  uint64_t count = 0;
+
+  for (const auto &entry : x86_linux_all_tdesc_features)
+    if (entry.is_x32)
+      ++count;
+
+  gdb_assert (count > 0);
+
+  return (1 << count);
+}
+
+#ifdef IN_PROCESS_AGENT
+
+/* See linux-x86-tdesc.h.  */
+
+int
+x86_linux_amd64_ipa_tdesc_count ()
+{
+  return x86_linux_amd64_tdesc_count ();
+}
+
+/* See linux-x86-tdesc.h.  */
+
+int
+x86_linux_x32_ipa_tdesc_count ()
+{
+  return x86_linux_x32_tdesc_count ();
+}
+
+/* See linux-x86-tdesc.h.  */
+
+int
+x86_linux_i386_ipa_tdesc_count ()
+{
+  return x86_linux_i386_tdesc_count ();
+}
+
+#endif /* IN_PROCESS_AGENT */
+
+/* Convert an xcr0 value into an integer.  The integer will be passed to
+   the in-process-agent where it will then be passed to
+   x86_linux_tdesc_idx_to_xcr0 to get back the xcr0 value.  */
+
+int
+x86_linux_xcr0_to_tdesc_idx (uint64_t xcr0)
+{
+  /* The following table shows which features are checked for when creating
+     the target descriptions (see nat/x86-linux-tdesc.c), the feature order
+     represents the bit order within the generated index number.
+
+     i386  | x87 sse mpx avx avx512 pkru
+     amd64 |         mpx avx avx512 pkru
+     i32   |             avx avx512 pkru
+
+     The features are ordered so that for each mode (i386, amd64, i32) the
+     generated index will form a continuous range.  */
+
+  int idx = 0;
+
+  for (int i = 0; i < ARRAY_SIZE (x86_linux_all_tdesc_features); ++i)
+    {
+      if ((xcr0 & x86_linux_all_tdesc_features[i].feature) != 0)
+	idx |= (1 << i);
+    }
+
+  return idx;
+}
+
+
+#ifdef IN_PROCESS_AGENT
+
+/* Convert an index number (as returned from x86_linux_xcr0_to_tdesc_idx)
+   into an xcr0 value which can then be used to create a target
+   description.  */
+
+uint64_t
+x86_linux_tdesc_idx_to_xcr0 (int idx)
+{
+  uint64_t xcr0 = 0;
+
+  for (int i = 0; i < ARRAY_SIZE (x86_linux_all_tdesc_features); ++i)
+    {
+      if ((idx & (1 << i)) != 0)
+	xcr0 |= x86_linux_all_tdesc_features[i].feature;
+    }
+
+  return xcr0;
+}
+
+#endif /* IN_PROCESS_AGENT */
+
+#if defined __i386__ || !defined IN_PROCESS_AGENT
+
+/* A cache of all possible i386 target descriptions.  */
+
+static struct target_desc *i386_tdescs[x86_linux_i386_tdesc_count ()] = { };
+
+/* See nat/x86-linux-tdesc.h.  */
+
+const struct target_desc *
+i386_linux_read_description (uint64_t xcr0)
+{
+  xcr0 &= x86_linux_i386_tdesc_feature_mask ();
+  int idx = x86_linux_xcr0_to_tdesc_idx (xcr0);
+
+  gdb_assert (idx >= 0 && idx < x86_linux_i386_tdesc_count ());
+
+  target_desc **tdesc = &i386_tdescs[idx];
+
+  if (*tdesc == nullptr)
+    {
+      *tdesc = i386_create_target_description (xcr0, true, false);
+
+      x86_linux_post_init_tdesc (*tdesc, false);
+    }
+
+  return *tdesc;
+}
+#endif
+
+#ifdef __x86_64__
+
+/* A cache of all possible amd64 target descriptions.  */
+
+static target_desc *amd64_tdescs[x86_linux_amd64_tdesc_count ()] = { };
+
+/* A cache of all possible x32 target descriptions.  */
+
+static target_desc *x32_tdescs[x86_linux_x32_tdesc_count ()] = { };
+
+/* See nat/x86-linux-tdesc.h.  */
+
+const struct target_desc *
+amd64_linux_read_description (uint64_t xcr0, bool is_x32)
+{
+  if (is_x32)
+    xcr0 &= x86_linux_x32_tdesc_feature_mask ();
+  else
+    xcr0 &= x86_linux_amd64_tdesc_feature_mask ();
+
+  int idx = x86_linux_xcr0_to_tdesc_idx (xcr0);
+
+  if (is_x32)
+    gdb_assert (idx >= 0 && idx < x86_linux_x32_tdesc_count ());
+  else
+    gdb_assert (idx >= 0 && idx < x86_linux_amd64_tdesc_count ());
+
+  target_desc **tdesc = nullptr;
+
+  if (is_x32)
+    tdesc = &x32_tdescs[idx];
+  else
+    tdesc = &amd64_tdescs[idx];
+
+  if (*tdesc == nullptr)
+    {
+      *tdesc = amd64_create_target_description (xcr0, is_x32, true, true);
+
+      x86_linux_post_init_tdesc (*tdesc, true);
+    }
+  return *tdesc;
+}
+
+#endif
diff --git a/gdb/nat/x86-linux-tdesc.h b/gdb/nat/x86-linux-tdesc.h
index 3727a8b..648fe0e 100644
--- a/gdb/nat/x86-linux-tdesc.h
+++ b/gdb/nat/x86-linux-tdesc.h
@@ -24,6 +24,8 @@
 
 struct target_desc;
 
+#ifndef IN_PROCESS_AGENT
+
 /* Return the target description for Linux thread TID.
 
    When *HAVE_PTRACE_GETREGSET is TRIBOOL_UNKNOWN then the current value of
@@ -57,19 +59,57 @@ x86_linux_tdesc_for_tid (int tid, enum tribool *have_ptrace_getregset,
 			 gdb::function_view<void (uint64_t)> xcr0_init_cb,
 			 const char *error_msg, uint64_t *xcr0_storage);
 
+#endif /* !IN_PROCESS_AGENT */
+
 #ifdef __x86_64__
 
-/* Return the right amd64-linux target descriptions according to
-   XCR0_FEATURES_BIT and IS_X32.  This is implemented separately in both
-   GDB and gdbserver.  */
+/* Return the AMD64 target descriptions corresponding to XCR0 and IS_X32.  */
 
-extern const target_desc *amd64_linux_read_description
-	(uint64_t xcr0_features_bit, bool is_x32);
+extern const target_desc *amd64_linux_read_description (uint64_t xcr0,
+							bool is_x32);
 
-#endif
+#endif /* __x86_64__ */
+
+/* Return the i386 target description corresponding to XCR0.  */
 
-/* Return the target description according to XCR0.  This is implemented
-   separately in both GDB and gdbserver.  */
 extern const struct target_desc *i386_linux_read_description (uint64_t xcr0);
 
+/* This function is called from amd64_linux_read_description and
+   i386_linux_read_description after a new target description has been
+   created, TDESC is the new target description, IS_64BIT will be true
+   when called from amd64_linux_read_description, otherwise IS_64BIT will
+   be false.  If the *_linux_read_description functions found a cached
+   target description then this function will not be called.
+
+   Both GDB and gdbserver have their own implementations of this
+   function.  */
+
+extern void x86_linux_post_init_tdesc (target_desc *tdesc, bool is_64bit);
+
+/* Convert an xcr0 value into an integer.  The integer will be passed to
+   the in-process-agent where it will then be passed to
+   x86_linux_tdesc_idx_to_xcr0 to get back the xcr0 value.  */
+
+extern int x86_linux_xcr0_to_tdesc_idx (uint64_t xcr0);
+
+
+#ifdef IN_PROCESS_AGENT
+
+/* Convert an index number (as returned from x86_linux_xcr0_to_tdesc_idx)
+   into an xcr0 value which can then be used to create a target
+   description.  */
+
+extern uint64_t x86_linux_tdesc_idx_to_xcr0 (int idx);
+
+/* Within the in-process-agent we need to pre-initialise all of the target
+   descriptions, to do this we need to know how many target descriptions
+   there are for each different target type.  These functions return the
+   target description count for the relevant target.  */
+
+extern int x86_linux_amd64_ipa_tdesc_count ();
+extern int x86_linux_x32_ipa_tdesc_count ();
+extern int x86_linux_i386_ipa_tdesc_count ();
+
+#endif /* IN_PROCESS_AGENT */
+
 #endif /* NAT_X86_LINUX_TDESC_H */