ctf: fix PR debug/112878

PR debug/112878: ICE: in ctf_add_slice, at ctfc.cc:499 with
_BitInt > 255 in a struct and -gctf1

The CTF generation in GCC does not have a mechanism to roll-back an
already added type.  In this testcase presented in the PR, we hit a
representation limit in CTF slices (for a member of a struct) and ICE,
after the type for struct (CTF_K_STRUCT) has already been added to the
container.

To exit gracefully instead, we now check for both the offset and size of
the bitfield to be explicitly <= 255.  If the check fails, we emit the
member with type CTF_K_UNKNOWN.  Note that, the value 255 stems from the
existing binutils libctf checks which were motivated to guard against
malformed inputs.

Although it is not accurate to say that this is a CTF representation
limit, mark the code with TBD_CTF_REPRESENTATION_LIMIT for now so that
this can be taken care of with the next format version bump, when
libctf's checks for the slice data can be lifted as well.

gcc/ChangeLog:
	PR debug/112878
	* dwarf2ctf.cc (gen_ctf_sou_type): Check for conditions before
	call to ctf_add_slice.  Use CTF_K_UNKNOWN type if fail.

gcc/testsuite/ChangeLog:
	PR debug/112878
	* gcc.dg/debug/ctf/ctf-bitfields-5.c: New test.

1 files changed, 10 insertions, 5 deletions

diff --git a/gcc/dwarf2ctf.cc b/gcc/dwarf2ctf.cc
index 77d6bf8..dc59569 100644
--- a/gcc/dwarf2ctf.cc
+++ b/gcc/dwarf2ctf.cc
@@ -606,11 +606,16 @@ gen_ctf_sou_type (ctf_container_ref ctfc, dw_die_ref sou, uint32_t kind)
 	      if (attr)
 		bitpos += AT_unsigned (attr);
 
-	      field_type_id = ctf_add_slice (ctfc, CTF_ADD_NONROOT,
-					     field_type_id,
-					     bitpos - field_location,
-					     bitsize,
-					     c);
+	      /* This is not precisely a TBD_CTF_REPRESENTATION_LIMIT, but
+		 surely something to look at for the next format version bump
+		 for CTF.  */
+	      if (bitsize <= 255 && (bitpos - field_location) <= 255)
+		field_type_id = ctf_add_slice (ctfc, CTF_ADD_NONROOT,
+					       field_type_id,
+					       bitpos - field_location,
+					       bitsize, c);
+	      else
+		field_type_id = gen_ctf_unknown_type (ctfc);
 	    }
 
 	  /* Add the field type to the struct or union type.  */