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, 25 insertions, 25 deletions

diff --git a/gdb/mips-tdep.c b/gdb/mips-tdep.c
index 071319c..9827026 100644
--- a/gdb/mips-tdep.c
+++ b/gdb/mips-tdep.c
@@ -227,7 +227,7 @@ static const char mips_disassembler_options_n64[] = "gpr-names=64";
 const struct mips_regnum *
 mips_regnum (struct gdbarch *gdbarch)
 {
-  mips_gdbarch_tdep *tdep = (mips_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  mips_gdbarch_tdep *tdep = gdbarch_tdep<mips_gdbarch_tdep> (gdbarch);
   return tdep->regnum;
 }
 
@@ -252,7 +252,7 @@ mips_float_register_p (struct gdbarch *gdbarch, int regnum)
 static bool
 mips_eabi (gdbarch *arch)
 {
-  mips_gdbarch_tdep *tdep = (mips_gdbarch_tdep *) gdbarch_tdep (arch);
+  mips_gdbarch_tdep *tdep = gdbarch_tdep<mips_gdbarch_tdep> (arch);
   return (tdep->mips_abi == MIPS_ABI_EABI32 \
 	  || tdep->mips_abi == MIPS_ABI_EABI64);
 }
@@ -260,21 +260,21 @@ mips_eabi (gdbarch *arch)
 static int
 mips_last_fp_arg_regnum (gdbarch *arch)
 {
-  mips_gdbarch_tdep *tdep = (mips_gdbarch_tdep *) gdbarch_tdep (arch);
+  mips_gdbarch_tdep *tdep = gdbarch_tdep<mips_gdbarch_tdep> (arch);
   return tdep->mips_last_fp_arg_regnum;
 }
 
 static int
 mips_last_arg_regnum (gdbarch *arch)
 {
-  mips_gdbarch_tdep *tdep = (mips_gdbarch_tdep *) gdbarch_tdep (arch);
+  mips_gdbarch_tdep *tdep = gdbarch_tdep<mips_gdbarch_tdep> (arch);
   return tdep->mips_last_arg_regnum;
 }
 
 static enum mips_fpu_type
 mips_get_fpu_type (gdbarch *arch)
 {
-  mips_gdbarch_tdep *tdep = (mips_gdbarch_tdep *) gdbarch_tdep (arch);
+  mips_gdbarch_tdep *tdep = gdbarch_tdep<mips_gdbarch_tdep> (arch);
   return tdep->mips_fpu_type;
 }
 
@@ -282,14 +282,14 @@ mips_get_fpu_type (gdbarch *arch)
 enum mips_abi
 mips_abi (struct gdbarch *gdbarch)
 {
-  mips_gdbarch_tdep *tdep = (mips_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  mips_gdbarch_tdep *tdep = gdbarch_tdep<mips_gdbarch_tdep> (gdbarch);
   return tdep->mips_abi;
 }
 
 int
 mips_isa_regsize (struct gdbarch *gdbarch)
 {
-  mips_gdbarch_tdep *tdep = (mips_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  mips_gdbarch_tdep *tdep = gdbarch_tdep<mips_gdbarch_tdep> (gdbarch);
 
   /* If we know how big the registers are, use that size.  */
   if (tdep->register_size_valid_p)
@@ -335,7 +335,7 @@ mips_abi_regsize (struct gdbarch *gdbarch)
 static int
 is_mips16_isa (struct gdbarch *gdbarch)
 {
-  mips_gdbarch_tdep *tdep = (mips_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  mips_gdbarch_tdep *tdep = gdbarch_tdep<mips_gdbarch_tdep> (gdbarch);
   return tdep->mips_isa == ISA_MIPS16;
 }
 
@@ -344,7 +344,7 @@ is_mips16_isa (struct gdbarch *gdbarch)
 static int
 is_micromips_isa (struct gdbarch *gdbarch)
 {
-  mips_gdbarch_tdep *tdep = (mips_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  mips_gdbarch_tdep *tdep = gdbarch_tdep<mips_gdbarch_tdep> (gdbarch);
   return tdep->mips_isa == ISA_MICROMIPS;
 }
 
@@ -636,7 +636,7 @@ static const char * const mips_linux_reg_names[NUM_MIPS_PROCESSOR_REGS] = {
 static const char *
 mips_register_name (struct gdbarch *gdbarch, int regno)
 {
-  mips_gdbarch_tdep *tdep = (mips_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  mips_gdbarch_tdep *tdep = gdbarch_tdep<mips_gdbarch_tdep> (gdbarch);
   /* GPR names for all ABIs other than n32/n64.  */
   static const char *mips_gpr_names[] = {
     "zero", "at", "v0", "v1", "a0", "a1", "a2", "a3",
@@ -777,7 +777,7 @@ mips_pseudo_register_read (struct gdbarch *gdbarch, readable_regcache *regcache,
   else if (register_size (gdbarch, rawnum) >
 	   register_size (gdbarch, cookednum))
     {
-      mips_gdbarch_tdep *tdep = (mips_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+      mips_gdbarch_tdep *tdep = gdbarch_tdep<mips_gdbarch_tdep> (gdbarch);
 
       if (tdep->mips64_transfers_32bit_regs_p)
 	return regcache->raw_read_part (rawnum, 0, 4, buf);
@@ -810,7 +810,7 @@ mips_pseudo_register_write (struct gdbarch *gdbarch,
   else if (register_size (gdbarch, rawnum) >
 	   register_size (gdbarch, cookednum))
     {
-      mips_gdbarch_tdep *tdep = (mips_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+      mips_gdbarch_tdep *tdep = gdbarch_tdep<mips_gdbarch_tdep> (gdbarch);
 
       if (tdep->mips64_transfers_32bit_regs_p)
 	regcache->raw_write_part (rawnum, 0, 4, buf);
@@ -855,7 +855,7 @@ mips_ax_pseudo_register_push_stack (struct gdbarch *gdbarch,
       if (register_size (gdbarch, rawnum) > register_size (gdbarch, reg))
 	{
 	  mips_gdbarch_tdep *tdep
-	    = (mips_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+	    = gdbarch_tdep<mips_gdbarch_tdep> (gdbarch);
 
 	  if (!tdep->mips64_transfers_32bit_regs_p
 	      || gdbarch_byte_order (gdbarch) != BFD_ENDIAN_BIG)
@@ -1059,7 +1059,7 @@ mips_register_type (struct gdbarch *gdbarch, int regnum)
   else
     {
       int rawnum = regnum - gdbarch_num_regs (gdbarch);
-      mips_gdbarch_tdep *tdep = (mips_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+      mips_gdbarch_tdep *tdep = gdbarch_tdep<mips_gdbarch_tdep> (gdbarch);
 
       /* The cooked or ABI registers.  These are sized according to
 	 the ABI (with a few complications).  */
@@ -1191,7 +1191,7 @@ show_mask_address (struct ui_file *file, int from_tty,
       else
 	{
 	  mips_gdbarch_tdep *tdep
-	    = (mips_gdbarch_tdep *) gdbarch_tdep (target_gdbarch ());
+	    = gdbarch_tdep<mips_gdbarch_tdep> (target_gdbarch ());
 
 	  if (mips_mask_address_p (tdep))
 	    additional_text = _(" (currently \"on\")");
@@ -1727,7 +1727,7 @@ mips32_next_pc (struct regcache *regcache, CORE_ADDR pc)
 	    case 12:            /* SYSCALL */
 	      {
 		mips_gdbarch_tdep *tdep
-		  = (mips_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+		  = gdbarch_tdep<mips_gdbarch_tdep> (gdbarch);
 
 		if (tdep->syscall_next_pc != NULL)
 		  pc = tdep->syscall_next_pc (get_current_frame ());
@@ -1938,7 +1938,7 @@ micromips_next_pc (struct regcache *regcache, CORE_ADDR pc)
 		case 0x22d: /* SYSCALL:  000000 1000101101 111100 */
 		  {
 		    mips_gdbarch_tdep *tdep
-		      = (mips_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+		      = gdbarch_tdep<mips_gdbarch_tdep> (gdbarch);
 
 		    if (tdep->syscall_next_pc != NULL)
 		      pc = tdep->syscall_next_pc (get_current_frame ());
@@ -3901,7 +3901,7 @@ mips_stub_frame_base_sniffer (struct frame_info *this_frame)
 static CORE_ADDR
 mips_addr_bits_remove (struct gdbarch *gdbarch, CORE_ADDR addr)
 {
-  mips_gdbarch_tdep *tdep = (mips_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  mips_gdbarch_tdep *tdep = gdbarch_tdep<mips_gdbarch_tdep> (gdbarch);
 
   if (mips_mask_address_p (tdep) && (((ULONGEST) addr) >> 32 == 0xffffffffUL))
     /* This hack is a work-around for existing boards using PMON, the
@@ -4804,7 +4804,7 @@ mips_eabi_return_value (struct gdbarch *gdbarch, struct value *function,
 			struct type *type, struct regcache *regcache,
 			gdb_byte *readbuf, const gdb_byte *writebuf)
 {
-  mips_gdbarch_tdep *tdep = (mips_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  mips_gdbarch_tdep *tdep = gdbarch_tdep<mips_gdbarch_tdep> (gdbarch);
   int fp_return_type = 0;
   int offset, regnum, xfer;
 
@@ -5195,7 +5195,7 @@ mips_n32n64_return_value (struct gdbarch *gdbarch, struct value *function,
 			  struct type *type, struct regcache *regcache,
 			  gdb_byte *readbuf, const gdb_byte *writebuf)
 {
-  mips_gdbarch_tdep *tdep = (mips_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  mips_gdbarch_tdep *tdep = gdbarch_tdep<mips_gdbarch_tdep> (gdbarch);
 
   /* From MIPSpro N32 ABI Handbook, Document Number: 007-2816-004
 
@@ -5704,7 +5704,7 @@ mips_o32_return_value (struct gdbarch *gdbarch, struct value *function,
 {
   CORE_ADDR func_addr = function ? find_function_addr (function, NULL) : 0;
   int mips16 = mips_pc_is_mips16 (gdbarch, func_addr);
-  mips_gdbarch_tdep *tdep = (mips_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  mips_gdbarch_tdep *tdep = gdbarch_tdep<mips_gdbarch_tdep> (gdbarch);
   enum mips_fval_reg fval_reg;
 
   fval_reg = readbuf ? mips16 ? mips_fval_gpr : mips_fval_fpr : mips_fval_both;
@@ -8101,7 +8101,7 @@ mips_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
   else if (arches != NULL)
     {
       mips_gdbarch_tdep *tdep
-	= (mips_gdbarch_tdep *) gdbarch_tdep (arches->gdbarch);
+	= gdbarch_tdep<mips_gdbarch_tdep> (arches->gdbarch);
       elf_flags = tdep->elf_flags;
     }
   else
@@ -8142,7 +8142,7 @@ mips_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
   if (found_abi == MIPS_ABI_UNKNOWN && info.abfd == NULL && arches != NULL)
     {
       mips_gdbarch_tdep *tdep
-	= (mips_gdbarch_tdep *) gdbarch_tdep (arches->gdbarch);
+	= gdbarch_tdep<mips_gdbarch_tdep> (arches->gdbarch);
       found_abi = tdep->found_abi;
     }
 
@@ -8459,7 +8459,7 @@ mips_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
        arches = gdbarch_list_lookup_by_info (arches->next, &info))
     {
       mips_gdbarch_tdep *tdep
-        = (mips_gdbarch_tdep *) gdbarch_tdep (arches->gdbarch);
+	= gdbarch_tdep<mips_gdbarch_tdep> (arches->gdbarch);
 
       /* MIPS needs to be pedantic about which ABI and the compressed
 	 ISA variation the object is using.  */
@@ -8917,7 +8917,7 @@ mips_fpu_type_str (enum mips_fpu_type fpu_type)
 static void
 mips_dump_tdep (struct gdbarch *gdbarch, struct ui_file *file)
 {
-  mips_gdbarch_tdep *tdep = (mips_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  mips_gdbarch_tdep *tdep = gdbarch_tdep<mips_gdbarch_tdep> (gdbarch);
   if (tdep != NULL)
     {
       int ef_mips_arch;