[Bug gdb/21946] New: Python API search_memory remote targets bug

["dominik.b.czarnota+bugzilla at gmail dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=21946

            Bug ID: 21946
           Summary: Python API search_memory remote targets bug
           Product: gdb
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: gdb
          Assignee: unassigned at sourceware dot org
          Reporter: dominik.b.czarnota+bugzilla at gmail dot com
  Target Milestone: ---

Hey,

There is a bug with `gdb.selected_inferior().search_memory(startaddr, size,
searchfor)` returning wrong results in some cases for remote targets.

To reproduce:

1. In first console launch `gdbserver localhost:4444 /bin/ls`

2. In second console fire:

```
$ gdb /bin/ls
Reading symbols from /bin/ls...(no debugging symbols found)...done.
(gdb) target remote localhost:4444
Remote debugging using localhost:4444
Reading /lib64/ld-linux-x86-64.so.2 from remote target...
warning: File transfers from remote targets can be slow. Use "set sysroot" to
access files locally instead.
Reading /lib64/ld-linux-x86-64.so.2 from remote target...
Reading symbols from target:/lib64/ld-linux-x86-64.so.2...(no debugging symbols
found)...done.
0x00007ff8582a6cc0 in _start () from target:/lib64/ld-linux-x86-64.so.2
(gdb) info proc mappings
process 11537
Mapped address spaces:

          Start Addr           End Addr       Size     Offset objfile
            0x400000           0x41f000    0x1f000        0x0 /usr/bin/ls
            0x61e000           0x620000     0x2000    0x1e000 /usr/bin/ls
            0x620000           0x621000     0x1000        0x0 [heap]
      0x7ff8582a6000     0x7ff8582c9000    0x23000        0x0
/usr/lib/ld-2.25.so
      0x7ff8584c4000     0x7ff8584c7000     0x3000        0x0 [vvar]
      0x7ff8584c7000     0x7ff8584c9000     0x2000        0x0 [vdso]
      0x7ff8584c9000     0x7ff8584cb000     0x2000    0x23000
/usr/lib/ld-2.25.so
      0x7ff8584cb000     0x7ff8584cc000     0x1000        0x0 
      0x7ffffffdd000     0x7ffffffff000    0x22000        0x0 [stack]
  0xffffffffff600000 0xffffffffff601000     0x1000        0x0 [vsyscall]
(gdb) #grab stack startaddr & size
(gdb) py import gdb; print("0x%x" %
gdb.selected_inferior().search_memory(0x7ffffffdd000, 0x22000, "bin/"))
0x7f23050a3390
(gdb) # the address is invalid?
(gdb) x/s 0x7f23050a3390
0x7f23050a3390: <error: Cannot access memory at address 0x7f23050a3390>
(gdb) x/xg 0x7f23050a3390
0x7f23050a3390: Cannot access memory at address 0x7f23050a3390
(gdb) set remote search-memory-packet off
(gdb) py import gdb; print("0x%x" %
gdb.selected_inferior().search_memory(0x7ffffffdd000, 0x22000, "bin/"))
0x7fffffffdaba
(gdb) x/s 0x7fffffffdaba
0x7fffffffdaba: "bin/ls"
(gdb) 
```

Basically it seems that when the `remote search-memory-packet` parameter is
enabled, the search results are wrong.

I am not aware what does this option introduce, but it seems it is a good
workaround.

My GDB/Python version can be seen below:
```
pwndbg> version
Gdb: GNU gdb (GDB) 8.0
Python: 3.6.2 (default, Jul 20 2017, 03:52:27)  [GCC 7.1.1 20170630]
Pwndbg: 1.0.0 build: f481201
```

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