SB-C::REPACK-XREF breaks on an aref with an invalid index

[Attila Lendvai]

it happens only sometimes, probably depends on the actual code/symbols loaded.

SBCL is HEAD as of today: 98ae2f63f69fea4a72325734b8013eab71d22b57 (plus a couple of irrelevant changes)

SAVE-LISP-AND-DIE calls SB-C::REPACK-XREF, it breaks into the debugger with an error, i started a swank server, and in this state i can even reproduce it from a slime repl by calling it by hand with:

(SB-C::REPACK-XREF :COMPACT-NAME-COUNT 256 :VERBOSE NIL)

the actual access is this line (inside the lambda returned by index->name):

(aref vector (+ index 1 (- common-count)))

either VECTOR is not what it should be, or it's accessed with the wrong assumptions. maybe using typed structures, or explicit accessor functions would help avoiding this, or at least debugging such errors.

Invalid index 257 for (SIMPLE-VECTOR 2), should be a non-negative integer below 2.
   [Condition of type SB-INT:INVALID-ARRAY-INDEX-ERROR]

Restarts:
 2: RETRY Retry SLIME REPL evaluation request.
 1: *ABORT Return to SLIME's top level.
 0: ABORT abort thread (#<THREAD "repl-thread" RUNNING {1004D8FFA3}>)

Backtrace:
  0: ((SB-IMPL::OPTIMIZED-DATA-VECTOR-REF T) #<unavailable argument> #<unavailable argument>)
  1: ((LAMBDA (SB-INT:INDEX) :IN SB-C::INDEX->NAME) 256)
      Locals:
        SB-C::COMMON-COUNT = 0
        SB-INT:INDEX = 256
        VECTOR = #(#(9 3 1 128 18) SWANK-REPL::OPEN-STREAMS)
  2: (SB-C::MAP-PACKED-XREF-DATA #<CLOSURE (LAMBDA (SB-C::KIND SB-C::NAME NUMBER) :IN SB-C::REPACK-XREF) {1003FD02AB}> #(#(9 3 1 128 18) SWANK-REPL::OPEN-STREAMS))
      Locals:
        DECODER = #<CLOSURE (LAMBDA (INTEGER) :IN SB-C::INDEX-AND-NUMBER-DECODER) {1003FD02FB}>
        FUNCTION = #<CLOSURE (LAMBDA (SB-C::KIND SB-C::NAME NUMBER) :IN SB-C::REPACK-XREF) {1003FD02AB}>
        FUNCTION#1 = #<CLOSURE (LAMBDA (SB-C::KIND SB-C::NAME NUMBER) :IN SB-C::REPACK-XREF) {1003FD02AB}>
        INDEX = 256
        KIND = :CALLS
        KIND-NUMBER = 1
        LOOKUP = #<CLOSURE (LAMBDA (SB-INT:INDEX) :IN SB-C::INDEX->NAME) {1003FD02DB}>
        #:LOOP-REPEAT-28 = 0
        NUMBER = 4
        OFFSET = 5
        PACKED = #(9 3 1 128 18)
        RECORD-COUNT = 1
        XREF-DATA = #(#(9 3 1 128 18) SWANK-REPL::OPEN-STREAMS)
  3: ((LAMBDA (SB-C::NAME SB-C::FUN) :IN SB-C::REPACK-XREF) #<unused argument> #<FUNCTION SWANK-REPL::INITIALIZE-STREAMS-FOR-CONNECTION>)
      Locals:
        SB-C::ALL-UNPACKED = NIL
        SB-C::COUNTS = NIL
        SB-C::COUNTS-BY-NAME = #<HASH-TABLE :TEST EQUAL :COUNT 0 {1003F75B93}>
        SB-C::FUN = #<FUNCTION SWANK-REPL::INITIALIZE-STREAMS-FOR-CONNECTION>
        SB-C::OLD-SIZE = 21
        SB-C::SEEN = #<HASH-TABLE :TEST EQUAL :COUNT 0 {1003FD01E3}>
        SB-C::UNPACKED = NIL
        SB-C::XREFS = #(#(9 3 1 128 18) SWANK-REPL::OPEN-STREAMS)
  4: (SB-C::CALL-WITH-EACH-GLOBALDB-NAME #<CLOSURE (LAMBDA (SB-C::NAME) :IN SB-C::MAP-SIMPLE-FUNS) {1003F75CAB}>)
  5: (SB-C::REPACK-XREF :COMPACT-NAME-COUNT 256 :VERBOSE NIL)
      Locals:
        #:.DEFAULTING-TEMP. = 256
        #:.DEFAULTING-TEMP.#1 = NIL
        ALL-UNPACKED = NIL
        COMPACT-NAME-COUNT = 256
        COUNTS = NIL
        COUNTS-BY-NAME = #<HASH-TABLE :TEST EQUAL :COUNT 0 {1003F75B93}>
        NEW-SIZE = 0
        OLD-SIZE = 21