[Bug symtab/18392] New: ../../gdb/dwarf2loc.c:834: internal-error: chain_candidate: Assertion `result->callers + result->callees < result->length' failed

[Bug symtab/18392] New: ../../gdb/dwarf2loc.c:834: internal-error: chain_candidate: Assertion `result->callers + result->callees < result->length' failed

[schwab@linux-m68k.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18392

            Bug ID: 18392
           Summary: ../../gdb/dwarf2loc.c:834: internal-error:
                    chain_candidate: Assertion `result->callers +
                    result->callees < result->length' failed
           Product: gdb
           Version: 7.9
            Status: NEW
          Severity: normal
          Priority: P2
         Component: symtab
          Assignee: unassigned at sourceware dot org
          Reporter: schwab@linux-m68k.org
                CC: jan.kratochvil at redhat dot com
  Target Milestone: ---

This assertion happend while debugging cc1.  The condition doesn't make sense,
since result is initialized with length == callers == callees.

DW_OP_GNU_entry_value resolving has found function "eliminate_regs_1(rtx_def*,
machine_mode, rtx_def*, bool, bool)" at 0x9d0e40 can call itself via tail calls
may_use_invariant=<optimized out>, for_costs=true)
    at ../../gcc/gcc/reload1.c:2917
tailcall: initial: 0x9d12de(eliminate_regs_1(rtx_def*, machine_mode, rtx_def*,
bool, bool))
tailcall: compare: 0x9d1108(eliminate_regs_1(rtx_def*, machine_mode, rtx_def*,
bool, bool)) 0x9d12de(eliminate_regs_1(rtx_def*, machine_mode, rtx_def*, bool,
bool))
tailcall: reduced: | 0x9d12de(eliminate_regs_1(rtx_def*, machine_mode,
rtx_def*, bool, bool))
../../gdb/dwarf2loc.c:830: internal-error: chain_candidate: Assertion
`result->callers + result->callees < result->length' failed.

(top-gdb) p *result
$11 = {callers = 0, callees = 1, length = 1, call_site = {0x278c230}}

-- 
You are receiving this mail because:
You are on the CC list for the bug.

[Bug symtab/18392] ../../gdb/dwarf2loc.c:834: internal-error: chain_candidate: Assertion `result->callers + result->callees < result->length' failed

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18392

--- Comment #1 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jan Kratochvil <jkratoch@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=e0619de699ae6e86d8b93fa96a7668aef2e9636a

commit e0619de699ae6e86d8b93fa96a7668aef2e9636a
Author: Jan Kratochvil <jan.kratochvil@redhat.com>
Date:   Mon Jun 1 14:02:34 2015 +0200

    PR symtab/18392

    Initially there is some chain (let's say the longest one
    but that doe snot matter).  Consequently its elements from the middle are
    being removed and there remains only some few unambiguous top and bottom
ones.

    The original idea why the comparison should be sharp ("<") was that if
there
    are multiple chains like (0xaddr show jmp instruction address):
            main(0x100) -> a(0x200) -> d(0x400)
            main(0x100) -> a(0x200) -> c(0x300) -> d(0x400)
    then - such situation cannot exist - if two jmp instructions in "a" have
the
    same address they must also jump to the same address (*).

    (*) jump to a computed address would be never considered for the DWARF
        tail-call records.

    So there could be:
            main(0x100) -> a(0x200) -> d(0x400)
            main(0x100) -> a(0x270) -> c(0x300) -> d(0x400)
    But then "a" frame itself is ambiguous and it must not be displayed.

    I did not realize that there can be self-tail-call:
            main(0x100) -> a(0x200) -> d(0x400)
            main(0x100) -> a(0x280) -> a(0x200) -> d(0x400)
    which intersects to:
            main(0x100) -> <???>? -> a(0x200) -> d(0x400)
    And so if the first chain was chosen the
            main(0x100) -> a(0x200) -> d(0x400)
    then the final intersection has callers+callees==length.

    > for example, if CALLERS is 3 and
    > CALLEES is 2, what does the chain look like?

    main(0x100) -> x(0x150) -> y(0x200) -> <???>? -> a(0x200) -> d(0x400)

    And if LENGTH is 7 then:
            call_site[0] = main(0x100)
            call_site[1] = x(0x150)
            call_site[2] = y(0x200)
            call_site[3] = garbage
            call_site[4] = garbage
            call_site[5] = a(0x200)
            call_site[6] = d(0x400)

    gdb/ChangeLog
    2015-06-01  Andreas Schwab  <schwab@linux-m68k.org>
            Jan Kratochvil  <jan.kratochvil@redhat.com>

        PR symtab/18392
        * dwarf2-frame-tailcall.c (pretended_chain_levels): Correct
        assertion.
        * dwarf2loc.c (chain_candidate): Likewise.

    gdb/testsuite/ChangeLog
    2015-06-01  Jan Kratochvil  <jan.kratochvil@redhat.com>

        PR symtab/18392
        * gdb.arch/amd64-tailcall-self.S: New file.
        * gdb.arch/amd64-tailcall-self.c: New file.
        * gdb.arch/amd64-tailcall-self.exp: New file.

-- 
You are receiving this mail because:
You are on the CC list for the bug.

[Bug symtab/18392] ../../gdb/dwarf2loc.c:834: internal-error: chain_candidate: Assertion `result->callers + result->callees < result->length' failed

[jan.kratochvil at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=18392

Jan Kratochvil <jan.kratochvil at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED
           Assignee|unassigned at sourceware dot org   |schwab@linux-m68k.org

--- Comment #2 from Jan Kratochvil <jan.kratochvil at redhat dot com> ---
Checked in.

-- 
You are receiving this mail because:
You are on the CC list for the bug.