[Bug runtime/31074] On aarch64 the systemtap.base/set_kernel.stp triggers "Unable to handle kernel paging request"

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

https://sourceware.org/bugzilla/show_bug.cgi?id=31074

William Cohen <wcohen at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED

--- Comment #2 from William Cohen <wcohen at redhat dot com> ---
Yes, it looked like the value might NULL + offset for field.  Added "-g
-save-temps" to EXTRA_CFLAGS of the make file of the save /tmp/stap* to get a
better idea of what the compiler is generating for code and where things are
located.

for the get_buffer:
        adrp    x3, .LANCHOR0
        add     x3, x3, :lo12:.LANCHOR0
        add     x3, x3, 568
        mov     x2, 512
        mov     x0, x3
        mov     w1, 0
.LVL175:
        .loc 23 1963 178 discriminator 1 view .LVU775
        bl      memset

get_tracepoint (static tracepoint_table)

.LVL489:
        .loc 27 127 36 view .LVU2068
        adrp    x1, .LANCHOR0
        add     x1, x1, :lo12:.LANCHOR0
        add     x1, x1, 1080
        ldr     x19, [x1, x0, lsl 3]

One thought that crossed my mind is that the memset code is pretty optimized
using cacheline zeroing for specific memset(x, 0, size) operations and might be
overrunning the end the static buffer into the static tracepoint_table as
buffer is not aligned to cache boundaries.  However, reducing the size of the
get_buffer memset clearing didn't eliminate the problem.

Thinking probably should add some diagnostics to the stp_tracepoint.c to get a
better understanding how tracepoint_table entries are getting corrupted.

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