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, 27 insertions, 27 deletions

diff --git a/gdb/xtensa-tdep.c b/gdb/xtensa-tdep.c
index b655883..f881870 100644
--- a/gdb/xtensa-tdep.c
+++ b/gdb/xtensa-tdep.c
@@ -116,7 +116,7 @@ static unsigned int xtensa_debug_level = 0;
 static int
 windowing_enabled (struct gdbarch *gdbarch, unsigned int ps)
 {
-  xtensa_gdbarch_tdep *tdep = (xtensa_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  xtensa_gdbarch_tdep *tdep = gdbarch_tdep<xtensa_gdbarch_tdep> (gdbarch);
 
   /* If we know CALL0 ABI is set explicitly,  say it is Call0.  */
   if (tdep->call_abi == CallAbiCall0Only)
@@ -130,7 +130,7 @@ windowing_enabled (struct gdbarch *gdbarch, unsigned int ps)
 static int
 arreg_number (struct gdbarch *gdbarch, int a_regnum, ULONGEST wb)
 {
-  xtensa_gdbarch_tdep *tdep = (xtensa_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  xtensa_gdbarch_tdep *tdep = gdbarch_tdep<xtensa_gdbarch_tdep> (gdbarch);
   int arreg;
 
   arreg = a_regnum - tdep->a0_base;
@@ -145,7 +145,7 @@ arreg_number (struct gdbarch *gdbarch, int a_regnum, ULONGEST wb)
 static int
 areg_number (struct gdbarch *gdbarch, int ar_regnum, unsigned int wb)
 {
-  xtensa_gdbarch_tdep *tdep = (xtensa_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  xtensa_gdbarch_tdep *tdep = gdbarch_tdep<xtensa_gdbarch_tdep> (gdbarch);
   int areg;
 
   areg = ar_regnum - tdep->ar_base;
@@ -226,7 +226,7 @@ static int
 xtensa_find_register_by_name (struct gdbarch *gdbarch, const char *name)
 {
   int i;
-  xtensa_gdbarch_tdep *tdep = (xtensa_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  xtensa_gdbarch_tdep *tdep = gdbarch_tdep<xtensa_gdbarch_tdep> (gdbarch);
 
   for (i = 0; i < gdbarch_num_cooked_regs (gdbarch); i++)
     if (strcasecmp (tdep->regmap[i].name, name) == 0)
@@ -239,7 +239,7 @@ xtensa_find_register_by_name (struct gdbarch *gdbarch, const char *name)
 static const char *
 xtensa_register_name (struct gdbarch *gdbarch, int regnum)
 {
-  xtensa_gdbarch_tdep *tdep = (xtensa_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  xtensa_gdbarch_tdep *tdep = gdbarch_tdep<xtensa_gdbarch_tdep> (gdbarch);
 
   /* Return the name stored in the register map.  */
   if (regnum >= 0 && regnum < gdbarch_num_cooked_regs (gdbarch))
@@ -254,7 +254,7 @@ xtensa_register_name (struct gdbarch *gdbarch, int regnum)
 static struct type *
 xtensa_register_type (struct gdbarch *gdbarch, int regnum)
 {
-  xtensa_gdbarch_tdep *tdep = (xtensa_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  xtensa_gdbarch_tdep *tdep = gdbarch_tdep<xtensa_gdbarch_tdep> (gdbarch);
 
   /* Return signed integer for ARx and Ax registers.  */
   if ((regnum >= tdep->ar_base
@@ -339,7 +339,7 @@ static int
 xtensa_reg_to_regnum (struct gdbarch *gdbarch, int regnum)
 {
   int i;
-  xtensa_gdbarch_tdep *tdep = (xtensa_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  xtensa_gdbarch_tdep *tdep = gdbarch_tdep<xtensa_gdbarch_tdep> (gdbarch);
 
   if (regnum >= 0 && regnum < 16)
     return tdep->a0_base + regnum;
@@ -542,7 +542,7 @@ xtensa_pseudo_register_read (struct gdbarch *gdbarch,
 {
   DEBUGTRACE ("xtensa_pseudo_register_read (... regnum = %d (%s) ...)\n",
 	      regnum, xtensa_register_name (gdbarch, regnum));
-  xtensa_gdbarch_tdep *tdep = (xtensa_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  xtensa_gdbarch_tdep *tdep = gdbarch_tdep<xtensa_gdbarch_tdep> (gdbarch);
 
   /* Read aliases a0..a15, if this is a Windowed ABI.  */
   if (tdep->isa_use_windowed_registers
@@ -634,7 +634,7 @@ xtensa_pseudo_register_write (struct gdbarch *gdbarch,
 {
   DEBUGTRACE ("xtensa_pseudo_register_write (... regnum = %d (%s) ...)\n",
 	      regnum, xtensa_register_name (gdbarch, regnum));
-  xtensa_gdbarch_tdep *tdep = (xtensa_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  xtensa_gdbarch_tdep *tdep = gdbarch_tdep<xtensa_gdbarch_tdep> (gdbarch);
 
   /* Renumber register, if aliases a0..a15 on Windowed ABI.  */
   if (tdep->isa_use_windowed_registers
@@ -767,7 +767,7 @@ xtensa_register_reggroup_p (struct gdbarch *gdbarch,
 			    int regnum,
 			    const struct reggroup *group)
 {
-  xtensa_gdbarch_tdep *tdep = (xtensa_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  xtensa_gdbarch_tdep *tdep = gdbarch_tdep<xtensa_gdbarch_tdep> (gdbarch);
   xtensa_register_t* reg = &tdep->regmap[regnum];
   xtensa_register_type_t type = reg->type;
   xtensa_register_group_t rg = reg->group;
@@ -821,7 +821,7 @@ xtensa_supply_gregset (const struct regset *regset,
 {
   const xtensa_elf_gregset_t *regs = (const xtensa_elf_gregset_t *) gregs;
   struct gdbarch *gdbarch = rc->arch ();
-  xtensa_gdbarch_tdep *tdep = (xtensa_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  xtensa_gdbarch_tdep *tdep = gdbarch_tdep<xtensa_gdbarch_tdep> (gdbarch);
   int i;
 
   DEBUGTRACE ("xtensa_supply_gregset (..., regnum==%d, ...)\n", regnum);
@@ -1050,7 +1050,7 @@ static struct frame_id
 xtensa_dummy_id (struct gdbarch *gdbarch, struct frame_info *this_frame)
 {
   CORE_ADDR pc, fp;
-  xtensa_gdbarch_tdep *tdep = (xtensa_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  xtensa_gdbarch_tdep *tdep = gdbarch_tdep<xtensa_gdbarch_tdep> (gdbarch);
 
   /* THIS-FRAME is a dummy frame.  Return a frame ID of that frame.  */
 
@@ -1105,7 +1105,7 @@ xtensa_scan_prologue (struct gdbarch *gdbarch, CORE_ADDR current_pc)
 {
 #define RETURN_FP goto done
 
-  xtensa_gdbarch_tdep *tdep = (xtensa_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  xtensa_gdbarch_tdep *tdep = gdbarch_tdep<xtensa_gdbarch_tdep> (gdbarch);
   unsigned int fp_regnum = tdep->a0_base + 1;
   CORE_ADDR start_addr;
   xtensa_isa isa;
@@ -1255,7 +1255,7 @@ xtensa_frame_cache (struct frame_info *this_frame, void **this_cache)
   if (windowed)
     {
       LONGEST op1;
-      xtensa_gdbarch_tdep *tdep = (xtensa_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+      xtensa_gdbarch_tdep *tdep = gdbarch_tdep<xtensa_gdbarch_tdep> (gdbarch);
 
       /* Get WINDOWBASE, WINDOWSTART, and PS registers.  */
       wb = get_frame_register_unsigned (this_frame, 
@@ -1417,7 +1417,7 @@ xtensa_frame_prev_register (struct frame_info *this_frame,
   struct xtensa_frame_cache *cache;
   ULONGEST saved_reg = 0;
   int done = 1;
-  xtensa_gdbarch_tdep *tdep = (xtensa_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  xtensa_gdbarch_tdep *tdep = gdbarch_tdep<xtensa_gdbarch_tdep> (gdbarch);
 
   if (*this_cache == NULL)
     *this_cache = xtensa_frame_cache (this_frame, this_cache);
@@ -1546,7 +1546,7 @@ xtensa_extract_return_value (struct type *type,
 
   gdb_assert(len > 0);
 
-  xtensa_gdbarch_tdep *tdep = (xtensa_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  xtensa_gdbarch_tdep *tdep = gdbarch_tdep<xtensa_gdbarch_tdep> (gdbarch);
   if (tdep->call_abi != CallAbiCall0Only)
     {
       /* First, we have to find the caller window in the register file.  */
@@ -1602,7 +1602,7 @@ xtensa_store_return_value (struct type *type,
 
   DEBUGTRACE ("xtensa_store_return_value (...)\n");
 
-  xtensa_gdbarch_tdep *tdep = (xtensa_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  xtensa_gdbarch_tdep *tdep = gdbarch_tdep<xtensa_gdbarch_tdep> (gdbarch);
   if (tdep->call_abi != CallAbiCall0Only)
     {
       regcache_raw_read_unsigned 
@@ -1686,7 +1686,7 @@ xtensa_push_dummy_call (struct gdbarch *gdbarch,
 			CORE_ADDR struct_addr)
 {
   enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
-  xtensa_gdbarch_tdep *tdep = (xtensa_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  xtensa_gdbarch_tdep *tdep = gdbarch_tdep<xtensa_gdbarch_tdep> (gdbarch);
   int size, onstack_size;
   gdb_byte *buf = (gdb_byte *) alloca (16);
   CORE_ADDR ra, ps;
@@ -1935,7 +1935,7 @@ xtensa_push_dummy_call (struct gdbarch *gdbarch,
 static int
 xtensa_breakpoint_kind_from_pc (struct gdbarch *gdbarch, CORE_ADDR *pcptr)
 {
-  xtensa_gdbarch_tdep *tdep = (xtensa_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  xtensa_gdbarch_tdep *tdep = gdbarch_tdep<xtensa_gdbarch_tdep> (gdbarch);
 
   if (tdep->isa_use_density_instructions)
     return 2;
@@ -2182,7 +2182,7 @@ call0_track_op (struct gdbarch *gdbarch, xtensa_c0reg_t dst[], xtensa_c0reg_t sr
 {
   enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
   unsigned litbase, litaddr, litval;
-  xtensa_gdbarch_tdep *tdep = (xtensa_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  xtensa_gdbarch_tdep *tdep = gdbarch_tdep<xtensa_gdbarch_tdep> (gdbarch);
 
   switch (opclass)
     {
@@ -2557,7 +2557,7 @@ call0_frame_cache (struct frame_info *this_frame,
   CORE_ADDR body_pc=UINT_MAX;	/* PC, where prologue analysis stopped.  */
   CORE_ADDR sp, fp, ra;
   int fp_regnum = C0_SP, c0_hasfp = 0, c0_frmsz = 0, prev_sp = 0, to_stk;
-  xtensa_gdbarch_tdep *tdep = (xtensa_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  xtensa_gdbarch_tdep *tdep = gdbarch_tdep<xtensa_gdbarch_tdep> (gdbarch);
  
   sp = get_frame_register_unsigned
     (this_frame, tdep->a0_base + 1);
@@ -2710,7 +2710,7 @@ static int a11_was_saved;
 static void
 execute_l32e (struct gdbarch *gdbarch, int at, int as, int offset, CORE_ADDR wb)
 {
-  xtensa_gdbarch_tdep *tdep = (xtensa_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  xtensa_gdbarch_tdep *tdep = gdbarch_tdep<xtensa_gdbarch_tdep> (gdbarch);
   int atreg = arreg_number (gdbarch, tdep->a0_base + at, wb);
   int asreg = arreg_number (gdbarch, tdep->a0_base + as, wb);
   CORE_ADDR addr = xtensa_read_register (asreg) + offset;
@@ -2740,7 +2740,7 @@ execute_l32e (struct gdbarch *gdbarch, int at, int as, int offset, CORE_ADDR wb)
 static void
 execute_s32e (struct gdbarch *gdbarch, int at, int as, int offset, CORE_ADDR wb)
 {
-  xtensa_gdbarch_tdep *tdep = (xtensa_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  xtensa_gdbarch_tdep *tdep = gdbarch_tdep<xtensa_gdbarch_tdep> (gdbarch);
   int atreg = arreg_number (gdbarch, tdep->a0_base + at, wb);
   int asreg = arreg_number (gdbarch, tdep->a0_base + as, wb);
   CORE_ADDR addr = xtensa_read_register (asreg) + offset;
@@ -2774,7 +2774,7 @@ execute_code (struct gdbarch *gdbarch, CORE_ADDR current_pc, CORE_ADDR wb)
   xtensa_opcode opc;
   int insn_num = 0;
   void (*func) (struct gdbarch *, int, int, int, CORE_ADDR);
-  xtensa_gdbarch_tdep *tdep = (xtensa_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  xtensa_gdbarch_tdep *tdep = gdbarch_tdep<xtensa_gdbarch_tdep> (gdbarch);
 
   uint32_t at, as, offset;
 
@@ -2905,7 +2905,7 @@ xtensa_window_interrupt_frame_cache (struct frame_info *this_frame,
   CORE_ADDR ps, wb, ws, ra;
   int epc1_regnum, i, regnum;
   xtensa_exception_handler_t eh_type;
-  xtensa_gdbarch_tdep *tdep = (xtensa_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  xtensa_gdbarch_tdep *tdep = gdbarch_tdep<xtensa_gdbarch_tdep> (gdbarch);
 
   /* Read PS, WB, and WS from the hardware. Note that PS register
      must be present, if Windowed ABI is supported.  */
@@ -3019,7 +3019,7 @@ xtensa_skip_prologue (struct gdbarch *gdbarch, CORE_ADDR start_pc)
 
       CORE_ADDR end_func;
 
-      xtensa_gdbarch_tdep *tdep = (xtensa_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+      xtensa_gdbarch_tdep *tdep = gdbarch_tdep<xtensa_gdbarch_tdep> (gdbarch);
       if ((tdep->call_abi == CallAbiCall0Only)
 	  && call0_ret (start_pc, prologue_sal.end))
 	return start_pc;
@@ -3041,7 +3041,7 @@ xtensa_skip_prologue (struct gdbarch *gdbarch, CORE_ADDR start_pc)
 static void
 xtensa_verify_config (struct gdbarch *gdbarch)
 {
-  xtensa_gdbarch_tdep *tdep = (xtensa_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  xtensa_gdbarch_tdep *tdep = gdbarch_tdep<xtensa_gdbarch_tdep> (gdbarch);
   string_file log;
 
   /* Verify that we got a reasonable number of AREGS.  */