[Bug gdb/22647] New: Tab completion hangs with a gcc7 LTO elf

["halbert at halwitz dot org" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=22647

            Bug ID: 22647
           Summary: Tab completion hangs with a gcc7 LTO elf
           Product: gdb
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: gdb
          Assignee: unassigned at sourceware dot org
          Reporter: halbert at halwitz dot org
  Target Milestone: ---

Created attachment 10701
  --> https://sourceware.org/bugzilla/attachment.cgi?id=10701&action=edit
gdb-hang-gcc721.elf and gdb-ok-gcc631.elf

I have a an arm-none-eabi-gcc 7.2.1 .elf that causes gdb to hang when doing tab
completion.

Problem appears with various gdb's I tried:

1. arm-none-eabi-gdb 8.0.50-8.0.50.20171128-git. This gdb came with the GNU
Tools for Arm Embedded Processors 7-2017-q4-major release.
2. arm-none-eabi-gdb 7.2.1 20170904 (previous 2017 q2 ARM tools release)
3. gdb 7.11.1 (non-ARM) Ubuntu 7.11.1-0ubuntu1~16.5

A good and a bad .elf are attached in a .zip.

To reproduce, do:
$ gdb gdb-hang-gcc721.elf
(gdb) break mp_cal<tab>

When you press <tab>, gdb will start consuming 100% CPU. I waited for several
minutes with no effect. The process must be `kill -9`d to get rid of it. ^C
does not work.

I tried `set max-completions 5`, which works, and `50`, which still hangs.

The good .elf looks like this:
$ gdb gdb-ok-gcc631.elf
(gdb) break mp_cal<tab>l_

which completes with `l_` immediately (the symbol is still incomplete).

You can test this ARM .elf with x64 gdb; you don't need to use an ARM-specific
gdb.

Both .elf's are from the same large source tree. One was compiled with -flto
with arm-none-eabi-gcc 6.3.1, the other with -flto on7.2.1. If I turn off
-flto, the problem does not occur, so it's some issue with what -flto is
causing to be generated in the elf. Nevertheless, gdb shouldn't hang even if
the .elf is bad.

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