[Bug external/31520] [gdb/external] Handle kernel.yama.ptrace_scope != 0

["vries at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=31520

--- Comment #1 from Tom de Vries <vries at gcc dot gnu.org> ---
So, this is the problem:
...
$ sleep 60 & gdb -q -p $(pidof sleep)
[4] 1786
Attaching to process 1786
ptrace: Operation not permitted.
(gdb) 
...

And this is the solution using sudo:
...
$ sleep 60 & sudo gdb -q -p $(pidof sleep)
[1] 1986
Attaching to process 1986
Reading symbols from /usr/bin/sleep...
(No debugging symbols found in /usr/bin/sleep)
Reading symbols from /lib64/libc.so.6...
(No debugging symbols found in /lib64/libc.so.6)
Reading symbols from /lib64/ld-linux-x86-64.so.2...
(No debugging symbols found in /lib64/ld-linux-x86-64.so.2)
0x00007f2fd01d70ca in clock_nanosleep@GLIBC_2.2.5 () from /lib64/libc.so.6
Missing separate debuginfos, use: zypper install
coreutils-debuginfo-8.32-150400.7.5.x86_64
(gdb) shell whoami
root
(gdb) 
...

And this is a solution using ptrace capabilities:
...
# sleep 60 & ./sudo-allow-ptrace.sh gdb -q -p $(pidof sleep)
[1] 1925
+ sudo -E capsh '--caps=cap_setpcap,cap_setuid,cap_setgid+ep
cap_sys_ptrace+eip' --keep=1 --user=vries --addamb=cap_sys_ptrace --shell=gdb
-- -q -p 1925
Attaching to process 1925
Reading symbols from /usr/bin/sleep...
(No debugging symbols found in /usr/bin/sleep)
Reading symbols from /lib64/libc.so.6...
(No debugging symbols found in /lib64/libc.so.6)
Reading symbols from /lib64/ld-linux-x86-64.so.2...
(No debugging symbols found in /lib64/ld-linux-x86-64.so.2)
0x00007feb59fed0ca in clock_nanosleep@GLIBC_2.2.5 () from /lib64/libc.so.6
(gdb) shell whoami
vries
(gdb) 
...
where ./sudo-allow-ptrace.sh is:
...
#!/bin/sh

shell="$1"
shift

set -x

sudo \
    -E capsh \
    --caps="cap_setpcap,cap_setuid,cap_setgid+ep cap_sys_ptrace+eip" \
    --keep=1 \
    --user="$USER" \
    --addamb="cap_sys_ptrace" \
    --shell=$shell -- \
    "$@"
...

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