[Bug runtime/30777] Systemtap modules unable to run on systemtap supporting Intel CET IBT

["wcohen at redhat dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=30777

--- Comment #1 from William Cohen <wcohen at redhat dot com> ---
When comparing the output of objdump of the
/usr/lib/debug/lib/modules/6.4.10-200.fc38.x86_64/vmlinux and the dmesg "Code
:" it appears that the ENDBR64 and the 
call to __fentry__ get overwrite with a multibyte nop:

from the objdump -d /usr/lib/debug/lib/modules/6.4.10-200.fc38.x86_64/vmlinux

ffffffff81206980 <kallsyms_lookup_name>:
kallsyms_lookup_name():
/usr/src/debug/kernel-6.4.10/linux-6.4.10-200.fc38.x86_64/kernel/kallsyms.c:271
ffffffff81206980:       f3 0f 1e fa             endbr64
ffffffff81206984:       e8 27 dc e7 ff          call   ffffffff810845b0
<__fentry__>
ffffffff81206989:       53                      push   %rbx
ffffffff8120698a:       48 83 ec 10             sub    $0x10,%rsp

From the dmesg output:

Code: 79 0a 48 f7 d0 48 03 05 d6 41 5b 01 c3 cc cc cc cc 66 0f 1f 84 00 00 00
00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 <66> 0f 1f 00 0f 1f 44 00
00 53 48 83 ec 10 65 48 8b 04 25 28 00 00

Working through to match up objdump and dmesg output:

<66> 0f 1f 00 0f 1f 44 00 00  nopw   0x0(%rax,%rax,1)  # *doesn't match
original code*
53                            push   %rbx  
48 83 ec 10                   sub    %0x10,$rsp
65 48 8b 04 25 28 00          mov    %gs:0x28,%rax

Something has changed the entry for kallsyms_lookup_name.  Internal kernel
calls to the function still work because those are not using indirect calls
(call *%reg).

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