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, 13 insertions, 13 deletions

diff --git a/gdb/riscv-tdep.c b/gdb/riscv-tdep.c
index 69f2123..2d41be9 100644
--- a/gdb/riscv-tdep.c
+++ b/gdb/riscv-tdep.c
@@ -733,7 +733,7 @@ show_riscv_debug_variable (struct ui_file *file, int from_tty,
 int
 riscv_isa_xlen (struct gdbarch *gdbarch)
 {
-  riscv_gdbarch_tdep *tdep = (riscv_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  riscv_gdbarch_tdep *tdep = gdbarch_tdep<riscv_gdbarch_tdep> (gdbarch);
   return tdep->isa_features.xlen;
 }
 
@@ -742,7 +742,7 @@ riscv_isa_xlen (struct gdbarch *gdbarch)
 int
 riscv_abi_xlen (struct gdbarch *gdbarch)
 {
-  riscv_gdbarch_tdep *tdep = (riscv_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  riscv_gdbarch_tdep *tdep = gdbarch_tdep<riscv_gdbarch_tdep> (gdbarch);
   return tdep->abi_features.xlen;
 }
 
@@ -751,7 +751,7 @@ riscv_abi_xlen (struct gdbarch *gdbarch)
 int
 riscv_isa_flen (struct gdbarch *gdbarch)
 {
-  riscv_gdbarch_tdep *tdep = (riscv_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  riscv_gdbarch_tdep *tdep = gdbarch_tdep<riscv_gdbarch_tdep> (gdbarch);
   return tdep->isa_features.flen;
 }
 
@@ -760,7 +760,7 @@ riscv_isa_flen (struct gdbarch *gdbarch)
 int
 riscv_abi_flen (struct gdbarch *gdbarch)
 {
-  riscv_gdbarch_tdep *tdep = (riscv_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  riscv_gdbarch_tdep *tdep = gdbarch_tdep<riscv_gdbarch_tdep> (gdbarch);
   return tdep->abi_features.flen;
 }
 
@@ -769,7 +769,7 @@ riscv_abi_flen (struct gdbarch *gdbarch)
 bool
 riscv_abi_embedded (struct gdbarch *gdbarch)
 {
-  riscv_gdbarch_tdep *tdep = (riscv_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  riscv_gdbarch_tdep *tdep = gdbarch_tdep<riscv_gdbarch_tdep> (gdbarch);
   return tdep->abi_features.embedded;
 }
 
@@ -786,7 +786,7 @@ riscv_has_fp_regs (struct gdbarch *gdbarch)
 static bool
 riscv_has_fp_abi (struct gdbarch *gdbarch)
 {
-  riscv_gdbarch_tdep *tdep = (riscv_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  riscv_gdbarch_tdep *tdep = gdbarch_tdep<riscv_gdbarch_tdep> (gdbarch);
   return tdep->abi_features.flen > 0;
 }
 
@@ -910,7 +910,7 @@ riscv_register_name (struct gdbarch *gdbarch, int regnum)
      will show up in 'info register all'.  Unless, we identify the
      duplicate copies of these registers (in riscv_tdesc_unknown_reg) and
      then hide the registers here by giving them no name.  */
-  riscv_gdbarch_tdep *tdep = (riscv_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  riscv_gdbarch_tdep *tdep = gdbarch_tdep<riscv_gdbarch_tdep> (gdbarch);
   if (tdep->duplicate_fflags_regnum == regnum)
     return NULL;
   if (tdep->duplicate_frm_regnum == regnum)
@@ -938,7 +938,7 @@ riscv_register_name (struct gdbarch *gdbarch, int regnum)
 static struct type *
 riscv_fpreg_d_type (struct gdbarch *gdbarch)
 {
-  riscv_gdbarch_tdep *tdep = (riscv_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  riscv_gdbarch_tdep *tdep = gdbarch_tdep<riscv_gdbarch_tdep> (gdbarch);
 
   if (tdep->riscv_fpreg_d_type == nullptr)
     {
@@ -1260,7 +1260,7 @@ riscv_is_regnum_a_named_csr (int regnum)
 static bool
 riscv_is_unknown_csr (struct gdbarch *gdbarch, int regnum)
 {
-  riscv_gdbarch_tdep *tdep = (riscv_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+  riscv_gdbarch_tdep *tdep = gdbarch_tdep<riscv_gdbarch_tdep> (gdbarch);
   return (regnum >= tdep->unknown_csrs_first_regnum
 	  && regnum < (tdep->unknown_csrs_first_regnum
 		       + tdep->unknown_csrs_count));
@@ -3600,7 +3600,7 @@ riscv_tdesc_unknown_reg (struct gdbarch *gdbarch, tdesc_feature *feature,
      record their register numbers here.  */
   if (strcmp (tdesc_feature_name (feature), riscv_freg_feature.name ()) == 0)
     {
-      riscv_gdbarch_tdep *tdep = (riscv_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+      riscv_gdbarch_tdep *tdep = gdbarch_tdep<riscv_gdbarch_tdep> (gdbarch);
       int *regnum_ptr = nullptr;
 
       if (strcmp (reg_name, "fflags") == 0)
@@ -3631,7 +3631,7 @@ riscv_tdesc_unknown_reg (struct gdbarch *gdbarch, tdesc_feature *feature,
      about register groups in riscv_register_reggroup_p.  */
   if (strcmp (tdesc_feature_name (feature), riscv_csr_feature.name ()) == 0)
     {
-      riscv_gdbarch_tdep *tdep = (riscv_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+      riscv_gdbarch_tdep *tdep = gdbarch_tdep<riscv_gdbarch_tdep> (gdbarch);
       if (tdep->unknown_csrs_first_regnum == -1)
 	tdep->unknown_csrs_first_regnum = possible_regnum;
       gdb_assert (tdep->unknown_csrs_first_regnum
@@ -3733,7 +3733,7 @@ riscv_gdbarch_init (struct gdbarch_info info,
 	 we are looking for.  If it doesn't then we can't reuse this
 	 gdbarch.  */
       riscv_gdbarch_tdep *other_tdep
-	= (riscv_gdbarch_tdep *) gdbarch_tdep (arches->gdbarch);
+	= gdbarch_tdep<riscv_gdbarch_tdep> (arches->gdbarch);
 
       if (other_tdep->isa_features != features
 	  || other_tdep->abi_features != abi_features)
@@ -3858,7 +3858,7 @@ riscv_next_pc (struct regcache *regcache, CORE_ADDR pc)
 {
   struct gdbarch *gdbarch = regcache->arch ();
   const riscv_gdbarch_tdep *tdep
-    = (riscv_gdbarch_tdep *) gdbarch_tdep (gdbarch);
+    = gdbarch_tdep<riscv_gdbarch_tdep> (gdbarch);
   struct riscv_insn insn;
   CORE_ADDR next_pc;