[Bug libctf/30226] New: CTF deduplication is incompatible with -femit-struct-debug-detailed=base

[nick.alcock at oracle dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=30226

            Bug ID: 30226
           Summary: CTF deduplication is incompatible with
                    -femit-struct-debug-detailed=base
           Product: binutils
           Version: 2.36
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libctf
          Assignee: unassigned at sourceware dot org
          Reporter: nick.alcock at oracle dot com
  Target Milestone: ---

Minimal reproducer:

[ibhagat@ibhagatpc final2]$ cat t.i
# 8 ""
typedef struct
{
  union
    {
      int addr4;
      int addr6[4];
    } u_ipaddr;
} KS_IPADDR;

KS_IPADDR KsSockOp_KsSockOp_op;
[ibhagat@ibhagatpc final2]$ rm -rf t.o; gcc -gctf -g -g -O2
-femit-struct-debug-detailed=base -o t.o -c t.i; ld -r -o temp_t.o t.o;
CTF error: /home/ibhagat/data1/gcc-temp/stacktrace/ctf/dbgrid/final2/ (0):
while emitting deduplicated forward, error emitting target type from input type
1
CTF error: deduplicating link type emission failed for
/home/ibhagat/data1/gcc-temp/stacktrace/ctf/dbgrid/final2/
ld: warning: CTF linking failed; output will have no CTF section: Type name
must not be empty.

This is because this option causes the emission of a typedef pointing to a
forward with no name, which is a bizarre artifact that is impossible to write
in plain C and which libctf prohibits the creation of:

    0x1: (kind 9) struct
    0x2: (kind 10) KS_IPADDR -> 0x1: (kind 9) struct

The deduplicator does its job and tries to emit this thing into the output, and
fails because it makes no sense. This is a good thing because had it worked the
result would have been wrong: all those empty structs would have been
considered identical and merged together, but in fact they should only be
considered identical to other struct KS_IPADDRs.

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