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, 21 insertions, 21 deletions

diff --git a/gdb/s390-tdep.c b/gdb/s390-tdep.c
index 14b03a1..2aeb3a1 100644
--- a/gdb/s390-tdep.c
+++ b/gdb/s390-tdep.c
@@ -1045,7 +1045,7 @@ s390_skip_prologue (struct gdbarch *gdbarch, CORE_ADDR pc)
 static int
 s390_register_call_saved (struct gdbarch *gdbarch, int regnum)
 {
-  s390_gdbarch_tdep *tdep = (s390_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  s390_gdbarch_tdep *tdep = gdbarch_tdep<s390_gdbarch_tdep> (gdbarch);
 
   switch (tdep->abi)
     {
@@ -1076,7 +1076,7 @@ s390_guess_tracepoint_registers (struct gdbarch *gdbarch,
 				 struct regcache *regcache,
 				 CORE_ADDR addr)
 {
-  s390_gdbarch_tdep *tdep = (s390_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  s390_gdbarch_tdep *tdep = gdbarch_tdep<s390_gdbarch_tdep> (gdbarch);
   int sz = register_size (gdbarch, S390_PSWA_REGNUM);
   gdb_byte *reg = (gdb_byte *) alloca (sz);
   ULONGEST pswm, pswa;
@@ -1172,7 +1172,7 @@ enum { s390_dwarf_reg_r0l = ARRAY_SIZE (s390_dwarf_regmap) - 16 };
 static int
 s390_dwarf_reg_to_regnum (struct gdbarch *gdbarch, int reg)
 {
-  s390_gdbarch_tdep *tdep = (s390_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  s390_gdbarch_tdep *tdep = gdbarch_tdep<s390_gdbarch_tdep> (gdbarch);
   int gdb_reg = -1;
 
   /* In a 32-on-64 debug scenario, debug info refers to the full
@@ -1231,7 +1231,7 @@ static struct value *
 s390_value_from_register (struct gdbarch *gdbarch, struct type *type,
 			  int regnum, struct frame_id frame_id)
 {
-  s390_gdbarch_tdep *tdep = (s390_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  s390_gdbarch_tdep *tdep = gdbarch_tdep<s390_gdbarch_tdep> (gdbarch);
   struct value *value = default_value_from_register (gdbarch, type,
 						     regnum, frame_id);
   check_typedef (type);
@@ -1250,7 +1250,7 @@ s390_value_from_register (struct gdbarch *gdbarch, struct type *type,
 static const char *
 s390_pseudo_register_name (struct gdbarch *gdbarch, int regnum)
 {
-  s390_gdbarch_tdep *tdep = (s390_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  s390_gdbarch_tdep *tdep = gdbarch_tdep<s390_gdbarch_tdep> (gdbarch);
 
   if (regnum == tdep->pc_regnum)
     return "pc";
@@ -1284,7 +1284,7 @@ s390_pseudo_register_name (struct gdbarch *gdbarch, int regnum)
 static struct type *
 s390_pseudo_register_type (struct gdbarch *gdbarch, int regnum)
 {
-  s390_gdbarch_tdep *tdep = (s390_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  s390_gdbarch_tdep *tdep = gdbarch_tdep<s390_gdbarch_tdep> (gdbarch);
 
   if (regnum == tdep->pc_regnum)
     return builtin_type (gdbarch)->builtin_func_ptr;
@@ -1308,7 +1308,7 @@ static enum register_status
 s390_pseudo_register_read (struct gdbarch *gdbarch, readable_regcache *regcache,
 			   int regnum, gdb_byte *buf)
 {
-  s390_gdbarch_tdep *tdep = (s390_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  s390_gdbarch_tdep *tdep = gdbarch_tdep<s390_gdbarch_tdep> (gdbarch);
   enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
   int regsize = register_size (gdbarch, regnum);
   ULONGEST val;
@@ -1383,7 +1383,7 @@ static void
 s390_pseudo_register_write (struct gdbarch *gdbarch, struct regcache *regcache,
 			    int regnum, const gdb_byte *buf)
 {
-  s390_gdbarch_tdep *tdep = (s390_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  s390_gdbarch_tdep *tdep = gdbarch_tdep<s390_gdbarch_tdep> (gdbarch);
   enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
   int regsize = register_size (gdbarch, regnum);
   ULONGEST val, psw;
@@ -1442,7 +1442,7 @@ static int
 s390_pseudo_register_reggroup_p (struct gdbarch *gdbarch, int regnum,
 				 const struct reggroup *group)
 {
-  s390_gdbarch_tdep *tdep = (s390_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  s390_gdbarch_tdep *tdep = gdbarch_tdep<s390_gdbarch_tdep> (gdbarch);
 
   /* We usually save/restore the whole PSW, which includes PC and CC.
      However, some older gdbservers may not support saving/restoring
@@ -1470,7 +1470,7 @@ static int
 s390_ax_pseudo_register_collect (struct gdbarch *gdbarch,
 				 struct agent_expr *ax, int regnum)
 {
-  s390_gdbarch_tdep *tdep = (s390_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  s390_gdbarch_tdep *tdep = gdbarch_tdep<s390_gdbarch_tdep> (gdbarch);
   if (regnum == tdep->pc_regnum)
     {
       ax_reg_mask (ax, S390_PSWA_REGNUM);
@@ -1504,7 +1504,7 @@ static int
 s390_ax_pseudo_register_push_stack (struct gdbarch *gdbarch,
 				    struct agent_expr *ax, int regnum)
 {
-  s390_gdbarch_tdep *tdep = (s390_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  s390_gdbarch_tdep *tdep = gdbarch_tdep<s390_gdbarch_tdep> (gdbarch);
   if (regnum == tdep->pc_regnum)
     {
       ax_reg (ax, S390_PSWA_REGNUM);
@@ -1905,7 +1905,7 @@ s390_push_dummy_call (struct gdbarch *gdbarch, struct value *function,
 		      function_call_return_method return_method,
 		      CORE_ADDR struct_addr)
 {
-  s390_gdbarch_tdep *tdep = (s390_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  s390_gdbarch_tdep *tdep = gdbarch_tdep<s390_gdbarch_tdep> (gdbarch);
   int word_size = gdbarch_ptr_bit (gdbarch) / 8;
   enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
   int i;
@@ -2084,7 +2084,7 @@ s390_return_value (struct gdbarch *gdbarch, struct value *function,
       break;
     case TYPE_CODE_ARRAY:
       {
-	s390_gdbarch_tdep *tdep = (s390_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+	s390_gdbarch_tdep *tdep = gdbarch_tdep<s390_gdbarch_tdep> (gdbarch);
 	rvc = (tdep->vector_abi == S390_VECTOR_ABI_128
 	       && TYPE_LENGTH (type) <= 16 && type->is_vector ())
 	  ? RETURN_VALUE_REGISTER_CONVENTION
@@ -2168,7 +2168,7 @@ s390_stack_frame_destroyed_p (struct gdbarch *gdbarch, CORE_ADDR pc)
 static CORE_ADDR
 s390_unwind_pc (struct gdbarch *gdbarch, struct frame_info *next_frame)
 {
-  s390_gdbarch_tdep *tdep = (s390_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  s390_gdbarch_tdep *tdep = gdbarch_tdep<s390_gdbarch_tdep> (gdbarch);
   ULONGEST pc;
   pc = frame_unwind_register_unsigned (next_frame, tdep->pc_regnum);
   return gdbarch_addr_bits_remove (gdbarch, pc);
@@ -2190,7 +2190,7 @@ static struct value *
 s390_unwind_pseudo_register (struct frame_info *this_frame, int regnum)
 {
   struct gdbarch *gdbarch = get_frame_arch (this_frame);
-  s390_gdbarch_tdep *tdep = (s390_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  s390_gdbarch_tdep *tdep = gdbarch_tdep<s390_gdbarch_tdep> (gdbarch);
   struct type *type = register_type (gdbarch, regnum);
 
   /* Unwind PC via PSW address.  */
@@ -2775,7 +2775,7 @@ static CORE_ADDR
 s390_record_address_mask (struct gdbarch *gdbarch, struct regcache *regcache,
 			  CORE_ADDR val)
 {
-  s390_gdbarch_tdep *tdep = (s390_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  s390_gdbarch_tdep *tdep = gdbarch_tdep<s390_gdbarch_tdep> (gdbarch);
   ULONGEST pswm, pswa;
   int am;
   if (tdep->abi == ABI_LINUX_S390)
@@ -2842,7 +2842,7 @@ s390_record_calc_disp_vsce (struct gdbarch *gdbarch, struct regcache *regcache,
 			    uint8_t vx, uint8_t el, uint8_t es, uint16_t bd,
 			    int8_t dh, CORE_ADDR *res)
 {
-  s390_gdbarch_tdep *tdep = (s390_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  s390_gdbarch_tdep *tdep = gdbarch_tdep<s390_gdbarch_tdep> (gdbarch);
   enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
   ULONGEST x;
   gdb_byte buf[16];
@@ -2885,7 +2885,7 @@ static int s390_popcnt (unsigned int x) {
 static int
 s390_record_gpr_g (struct gdbarch *gdbarch, struct regcache *regcache, int i)
 {
-  s390_gdbarch_tdep *tdep = (s390_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  s390_gdbarch_tdep *tdep = gdbarch_tdep<s390_gdbarch_tdep> (gdbarch);
   if (record_full_arch_list_add_reg (regcache, S390_R0_REGNUM + i))
     return -1;
   if (tdep->abi == ABI_LINUX_S390)
@@ -2899,7 +2899,7 @@ s390_record_gpr_g (struct gdbarch *gdbarch, struct regcache *regcache, int i)
 static int
 s390_record_gpr_h (struct gdbarch *gdbarch, struct regcache *regcache, int i)
 {
-  s390_gdbarch_tdep *tdep = (s390_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  s390_gdbarch_tdep *tdep = gdbarch_tdep<s390_gdbarch_tdep> (gdbarch);
   if (tdep->abi == ABI_LINUX_S390)
     {
       if (record_full_arch_list_add_reg (regcache, S390_R0_UPPER_REGNUM + i))
@@ -2939,7 +2939,7 @@ static int
 s390_process_record (struct gdbarch *gdbarch, struct regcache *regcache,
 		     CORE_ADDR addr)
 {
-  s390_gdbarch_tdep *tdep = (s390_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  s390_gdbarch_tdep *tdep = gdbarch_tdep<s390_gdbarch_tdep> (gdbarch);
   uint16_t insn[3] = {0};
   /* Instruction as bytes.  */
   uint8_t ibyte[6];
@@ -7178,7 +7178,7 @@ s390_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
        arches = gdbarch_list_lookup_by_info (arches->next, &info))
     {
       s390_gdbarch_tdep *tmp
-	= (s390_gdbarch_tdep *) gdbarch_tdep (arches->gdbarch);
+	= gdbarch_tdep<s390_gdbarch_tdep> (arches->gdbarch);
 
       if (!tmp)
 	continue;