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.

2 files changed, 27 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.  */
diff --git a/gcc/testsuite/gcc.dg/debug/ctf/ctf-bitfields-5.c b/gcc/testsuite/gcc.dg/debug/ctf/ctf-bitfields-5.c
new file mode 100644
index 0000000..fee8228
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/debug/ctf/ctf-bitfields-5.c
@@ -0,0 +1,17 @@
+/* Bitfield where the bit offset is > 255 is not allowed in CTF.
+
+   PR debug/112878.
+   This testcase is to ensure graceful handling. No slices are expected.  */
+
+/* { dg-do compile { target bitint } } */
+/* { dg-options "-O0 -gctf -dA" } */
+
+/* No slices are expected, but a struct with one member is expected.
+   CTF_K_UNKNOWN is also expected.  */
+/* { dg-final { scan-assembler-times "cts_type" 0 } } */
+/* { dg-final { scan-assembler-times "\[\t \]0x1a000001\[\t \]+\[^\n\]*ctt_info" 1 } } */
+/* { dg-final { scan-assembler-times "ascii \"unknown.0\"\[\t \]+\[^\n\]*ctf_string" 1 } } */
+
+struct {
+  _BitInt(282) a : 280;
+} b;