gdb: move the type cast into gdbarch_tdep

I built GDB for all targets on a x86-64/GNU-Linux system, and
then (accidentally) passed GDB a RISC-V binary, and asked GDB to "run"
the binary on the native target.  I got this error:

  (gdb) show architecture
  The target architecture is set to "auto" (currently "i386").
  (gdb) file /tmp/hello.rv32.exe
  Reading symbols from /tmp/hello.rv32.exe...
  (gdb) show architecture
  The target architecture is set to "auto" (currently "riscv:rv32").
  (gdb) run
  Starting program: /tmp/hello.rv32.exe
  ../../src/gdb/i387-tdep.c:596: internal-error: i387_supply_fxsave: Assertion `tdep->st0_regnum >= I386_ST0_REGNUM' failed.

What's going on here is this; initially the architecture is i386, this
is based on the default architecture, which is set based on the native
target.  After loading the RISC-V executable the architecture of the
current inferior is updated based on the architecture of the
executable.

When we "run", GDB does a fork & exec, with the inferior being
controlled through ptrace.  GDB sees an initial stop from the inferior
as soon as the inferior comes to life.  In response to this stop GDB
ends up calling save_stop_reason (linux-nat.c), which ends up trying
to read register from the inferior, to do this we end up calling
target_ops::fetch_registers, which, for the x86-64 native target,
calls amd64_linux_nat_target::fetch_registers.

After this I eventually end up in i387_supply_fxsave, different x86
based targets will end in different functions to fetch registers, but
it doesn't really matter which function we end up in, the problem is
this line, which is repeated in many places:

  i386_gdbarch_tdep *tdep = (i386_gdbarch_tdep *) gdbarch_tdep (arch);

The problem here is that the ARCH in this line comes from the current
inferior, which, as we discussed above, will be a RISC-V gdbarch, the
tdep field will actually be of type riscv_gdbarch_tdep, not
i386_gdbarch_tdep.  After this cast we are relying on undefined
behaviour, in my case I happen to trigger an assert, but this might
not always be the case.

The thing I tried that exposed this problem was of course, trying to
start an executable of the wrong architecture on a native target.  I
don't think that the correct solution for this problem is to detect,
at the point of cast, that the gdbarch_tdep object is of the wrong
type, but, I did wonder, is there a way that we could protect
ourselves from incorrectly casting the gdbarch_tdep object?

I think that there is something we can do here, and this commit is the
first step in that direction, though no actual check is added by this
commit.

This commit can be split into two parts:

 (1) In gdbarch.h and arch-utils.c.  In these files I have modified
 gdbarch_tdep (the function) so that it now takes a template argument,
 like this:

    template<typename TDepType>
    static inline TDepType *
    gdbarch_tdep (struct gdbarch *gdbarch)
    {
      struct gdbarch_tdep *tdep = gdbarch_tdep_1 (gdbarch);
      return static_cast<TDepType *> (tdep);
    }

  After this change we are no better protected, but the cast is now
  done within the gdbarch_tdep function rather than at the call sites,
  this leads to the second, much larger change in this commit,

  (2) Everywhere gdbarch_tdep is called, we make changes like this:

    -  i386_gdbarch_tdep *tdep = (i386_gdbarch_tdep *) gdbarch_tdep (arch);
    +  i386_gdbarch_tdep *tdep = gdbarch_tdep<i386_gdbarch_tdep> (arch);

There should be no functional change after this commit.

In the next commit I will build on this change to add an assertion in
gdbarch_tdep that checks we are casting to the correct type.

1 files changed, 19 insertions, 19 deletions

diff --git a/gdb/m68k-tdep.c b/gdb/m68k-tdep.c
index 568bde66f93..9e59f5904c3 100644
--- a/gdb/m68k-tdep.c
+++ b/gdb/m68k-tdep.c
@@ -70,7 +70,7 @@ typedef BP_MANIPULATION (m68k_break_insn) m68k_breakpoint;
 static struct type *
 m68k_ps_type (struct gdbarch *gdbarch)
 {
-  m68k_gdbarch_tdep *tdep = (m68k_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  m68k_gdbarch_tdep *tdep = gdbarch_tdep<m68k_gdbarch_tdep> (gdbarch);
 
   if (!tdep->m68k_ps_type)
     {
@@ -99,7 +99,7 @@ m68k_ps_type (struct gdbarch *gdbarch)
 static struct type *
 m68881_ext_type (struct gdbarch *gdbarch)
 {
-  m68k_gdbarch_tdep *tdep = (m68k_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  m68k_gdbarch_tdep *tdep = gdbarch_tdep<m68k_gdbarch_tdep> (gdbarch);
 
   if (!tdep->m68881_ext_type)
     tdep->m68881_ext_type
@@ -120,7 +120,7 @@ m68881_ext_type (struct gdbarch *gdbarch)
 static struct type *
 m68k_register_type (struct gdbarch *gdbarch, int regnum)
 {
-  m68k_gdbarch_tdep *tdep = (m68k_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  m68k_gdbarch_tdep *tdep = gdbarch_tdep<m68k_gdbarch_tdep> (gdbarch);
 
   if (tdep->fpregs_present)
     {
@@ -171,7 +171,7 @@ static const char * const m68k_register_names[] = {
 static const char *
 m68k_register_name (struct gdbarch *gdbarch, int regnum)
 {
-  m68k_gdbarch_tdep *tdep = (m68k_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  m68k_gdbarch_tdep *tdep = gdbarch_tdep<m68k_gdbarch_tdep> (gdbarch);
 
   if (regnum < 0 || regnum >= ARRAY_SIZE (m68k_register_names))
     internal_error (__FILE__, __LINE__,
@@ -191,7 +191,7 @@ static int
 m68k_convert_register_p (struct gdbarch *gdbarch,
 			 int regnum, struct type *type)
 {
-  m68k_gdbarch_tdep *tdep = (m68k_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  m68k_gdbarch_tdep *tdep = gdbarch_tdep<m68k_gdbarch_tdep> (gdbarch);
 
   if (!tdep->fpregs_present)
     return 0;
@@ -300,7 +300,7 @@ m68k_extract_return_value (struct type *type, struct regcache *regcache,
   if (type->code () == TYPE_CODE_PTR && len == 4)
     {
       struct gdbarch *gdbarch = regcache->arch ();
-      m68k_gdbarch_tdep *tdep = (m68k_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+      m68k_gdbarch_tdep *tdep = gdbarch_tdep<m68k_gdbarch_tdep> (gdbarch);
       regcache->raw_read (tdep->pointer_result_regnum, valbuf);
     }
   else if (len <= 4)
@@ -325,7 +325,7 @@ m68k_svr4_extract_return_value (struct type *type, struct regcache *regcache,
 {
   gdb_byte buf[M68K_MAX_REGISTER_SIZE];
   struct gdbarch *gdbarch = regcache->arch ();
-  m68k_gdbarch_tdep *tdep = (m68k_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  m68k_gdbarch_tdep *tdep = gdbarch_tdep<m68k_gdbarch_tdep> (gdbarch);
 
   if (tdep->float_return && type->code () == TYPE_CODE_FLT)
     {
@@ -348,7 +348,7 @@ m68k_store_return_value (struct type *type, struct regcache *regcache,
   if (type->code () == TYPE_CODE_PTR && len == 4)
     {
       struct gdbarch *gdbarch = regcache->arch ();
-      m68k_gdbarch_tdep *tdep = (m68k_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+      m68k_gdbarch_tdep *tdep = gdbarch_tdep<m68k_gdbarch_tdep> (gdbarch);
       regcache->raw_write (tdep->pointer_result_regnum, valbuf);
       /* gdb historically also set D0 in the SVR4 case.  */
       if (tdep->pointer_result_regnum != M68K_D0_REGNUM)
@@ -371,7 +371,7 @@ m68k_svr4_store_return_value (struct type *type, struct regcache *regcache,
 			      const gdb_byte *valbuf)
 {
   struct gdbarch *gdbarch = regcache->arch ();
-  m68k_gdbarch_tdep *tdep = (m68k_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  m68k_gdbarch_tdep *tdep = gdbarch_tdep<m68k_gdbarch_tdep> (gdbarch);
 
   if (tdep->float_return && type->code () == TYPE_CODE_FLT)
     {
@@ -391,7 +391,7 @@ m68k_svr4_store_return_value (struct type *type, struct regcache *regcache,
 static int
 m68k_reg_struct_return_p (struct gdbarch *gdbarch, struct type *type)
 {
-  m68k_gdbarch_tdep *tdep = (m68k_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  m68k_gdbarch_tdep *tdep = gdbarch_tdep<m68k_gdbarch_tdep> (gdbarch);
   enum type_code code = type->code ();
   int len = TYPE_LENGTH (type);
 
@@ -469,7 +469,7 @@ m68k_svr4_return_value (struct gdbarch *gdbarch, struct value *function,
 			gdb_byte *readbuf, const gdb_byte *writebuf)
 {
   enum type_code code = type->code ();
-  m68k_gdbarch_tdep *tdep = (m68k_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  m68k_gdbarch_tdep *tdep = gdbarch_tdep<m68k_gdbarch_tdep> (gdbarch);
 
   /* Aggregates with a single member are always returned like their
      sole element.  */
@@ -541,7 +541,7 @@ m68k_push_dummy_call (struct gdbarch *gdbarch, struct value *function,
 		      function_call_return_method return_method,
 		      CORE_ADDR struct_addr)
 {
-  m68k_gdbarch_tdep *tdep = (m68k_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  m68k_gdbarch_tdep *tdep = gdbarch_tdep<m68k_gdbarch_tdep> (gdbarch);
   enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
   gdb_byte buf[4];
   int i;
@@ -596,7 +596,7 @@ m68k_push_dummy_call (struct gdbarch *gdbarch, struct value *function,
 static int
 m68k_dwarf_reg_to_regnum (struct gdbarch *gdbarch, int num)
 {
-  m68k_gdbarch_tdep *tdep = (m68k_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  m68k_gdbarch_tdep *tdep = gdbarch_tdep<m68k_gdbarch_tdep> (gdbarch);
 
   if (num < 8)
     /* d0..7 */
@@ -766,7 +766,7 @@ m68k_analyze_register_saves (struct gdbarch *gdbarch, CORE_ADDR pc,
 			     struct m68k_frame_cache *cache)
 {
   enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
-  m68k_gdbarch_tdep *tdep = (m68k_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  m68k_gdbarch_tdep *tdep = gdbarch_tdep<m68k_gdbarch_tdep> (gdbarch);
 
   if (cache->locals >= 0)
     {
@@ -1058,7 +1058,7 @@ m68k_get_longjmp_target (struct frame_info *frame, CORE_ADDR *pc)
   gdb_byte *buf;
   CORE_ADDR sp, jb_addr;
   struct gdbarch *gdbarch = get_frame_arch (frame);
-  m68k_gdbarch_tdep *tdep = (m68k_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  m68k_gdbarch_tdep *tdep = gdbarch_tdep<m68k_gdbarch_tdep> (gdbarch);
   enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
 
   if (tdep->jb_pc < 0)
@@ -1104,7 +1104,7 @@ m68k_return_in_first_hidden_param_p (struct gdbarch *gdbarch,
 void
 m68k_svr4_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
 {
-  m68k_gdbarch_tdep *tdep = (m68k_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  m68k_gdbarch_tdep *tdep = gdbarch_tdep<m68k_gdbarch_tdep> (gdbarch);
 
   /* SVR4 uses a different calling convention.  */
   set_gdbarch_return_value (gdbarch, m68k_svr4_return_value);
@@ -1122,7 +1122,7 @@ m68k_svr4_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
 static void
 m68k_embedded_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
 {
-  m68k_gdbarch_tdep *tdep = (m68k_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  m68k_gdbarch_tdep *tdep = gdbarch_tdep<m68k_gdbarch_tdep> (gdbarch);
 
   m68k_svr4_init_abi (info, gdbarch);
   tdep->pointer_result_regnum = M68K_D0_REGNUM;
@@ -1237,7 +1237,7 @@ m68k_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
        best_arch = gdbarch_list_lookup_by_info (best_arch->next, &info))
     {
       m68k_gdbarch_tdep *tdep
-	= (m68k_gdbarch_tdep *) gdbarch_tdep (best_arch->gdbarch);
+	= gdbarch_tdep<m68k_gdbarch_tdep> (best_arch->gdbarch);
 
       if (flavour != tdep->flavour)
 	continue;
@@ -1339,7 +1339,7 @@ m68k_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
 static void
 m68k_dump_tdep (struct gdbarch *gdbarch, struct ui_file *file)
 {
-  m68k_gdbarch_tdep *tdep = (m68k_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  m68k_gdbarch_tdep *tdep = gdbarch_tdep<m68k_gdbarch_tdep> (gdbarch);
 
   if (tdep == NULL)
     return;