[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 #3 from William Cohen <wcohen at redhat dot com> ---
Created attachment 15085
  --> https://sourceware.org/bugzilla/attachment.cgi?id=15085&action=edit
Partial implementation for the kallsyms_* indirect calls in runtime/sym.c

This patch addresses the indirect calls in the runtime/sym.c.  This is not
complete.  Did a search for the runtime doing additional lookups and indirect
calls.  Below is a list of the other variables used for indirect calls and
where the indirect calls are implemented.

  kallsyms_copy_to_kernel_nofault
    magic macro in runtime/linux/loc2c-runtime.h
  kallsyms_task_user_regset_view
    magic macro in runtime/linux/loc2c-runtime.h
  kallsyms_uprobe_register
    magic macro in linux/uprobes-inode.c
  kallsyms_uprobe_unregister
    magic macro in linux/uprobes-inode.c
  kallsyms_uprobe_get_swbp_addr
    magic macro in linux/uprobes-inode.c
  kallsyms_get_mm_exe_file
    task_finder_vma.c (looks workable)
  kallsyms_task_work_add
    magic macro stp_task_work.c
  kallsyms_task_work_cancel
    magic macro stp_task_work.c
  kallsyms_udelay_simple
    magic macro linux/runtime.h
  stack_trace_save_regs_fn
    stack.c
  kallsyms_wake_up_state
    magic macro stp_utrace.c
  kallsyms_signal_wake_up_state
    magic macro stp_utrace.c
  kallsyms_signal_wake_up
    magic macro stp_utrace.c
  kallsyms___lock_task_sighand
    magic macro stp_utrace.c

Some of these are implemented with a "magic macro" that just replaces the
function name with the indirect calls using the variable.  They don't deal with
the function arguments.  There might be changes in the arguments between
different versions of the kernel and this might simplify code generations. The
macros avoid those details by just changing the function name.  However, if
doing the wrappers link this initial patch would need to include the arguments
and deal with any changes (like kallsysms_lookup_name) in the arguments.

Another concern is that the IBT wrapper is going to slow things down operation.
 This might be noticeable for kallsyms_copy_to_kernel_nofault.

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