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.`systemtap` scripts using guru mode now compile more quickly
The `systemtap` guru mode liveness analysis uses the `dyninst` library to parse binaries. Newer kernels enable mitigation code with `CONFIG_RETPOLINE=y`, replacing traditional RET instructions, with jumps to a thunk. As a consequence, binary analysis took a much longer time due to the liveness analysis needing to examine all additional edges of the control flow graph introduced by the jumps to the thunk.
With this update, `systemtap` disables liveness analysis when the kernel code is using thunks and, as a result, `systemtap` scripts using guru mode compile more quickly.
There is a workaround in systemtap that avoids this issue:
commit 71f89cccaf464c250c4497b7ec2a8e245b6704c4 (HEAD -> master, origin/master, origin/HEAD)
Author: Frank Ch. Eigler <fche>
Date: Wed Apr 19 11:23:16 2023 -0400
BZ2180328: disable pass-2 dyninst liveness analysis on CONFIG_RETPOLINE kernels
As a stopgap measure, ameliorate the dramatic dyninst analysis time
required to liveness-check $var assignments in kernels compiled with
retpolines. Just skip the effort (with a warning).
See also: https://github.com/dyninst/dyninst/issues/1305 .
This should be fixed by the rebase of systemtap. The reproducer runs in a reasonable amount of time using a systemtap that includes that patch:
$ sudo time stap -v -g fork.stp -c "./ssh.exp bz1028643 bbb" -o fork.stp.log
Pass 1: parsed user script and 504 library scripts using 358256virt/153728res/16940shr/138804data kb, in 250usr/30sys/292real ms.
WARNING: liveness analysis skipped on CONFIG_RETPOLINE kernel /usr/lib/debug/lib/modules/4.18.0-486.el8.x86_64/vmlinux: identifier '$return' at fork.stp:23:9
source: $return = -1
^
Pass 2: analyzed script: 1 probe, 2 functions, 0 embeds, 0 globals using 424420virt/221316res/18092shr/204968data kb, in 960usr/80sys/1039real ms.
Pass 3: using cached /root/.systemtap/cache/d0/stap_d0695e7c49ad338c333097e4c14796f6_1447.c
Pass 4: using cached /root/.systemtap/cache/d0/stap_d0695e7c49ad338c333097e4c14796f6_1447.ko
Pass 5: starting run.
spawn ssh -o ConnectTimeout=10 bz1028643@localhost pwd
Connection closed by ::1 port 22
Pass 5: run completed in 10usr/20sys/347real ms.
1.35user 0.15system 0:01.82elapsed 82%CPU (0avgtext+0avgdata 489836maxresident)k
0inputs+2776outputs (0major+58601minor)pagefaults 0swaps
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory (systemtap bug fix and enhancement update), and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.
https://access.redhat.com/errata/RHBA-2023:6952
There is a workaround in systemtap that avoids this issue: commit 71f89cccaf464c250c4497b7ec2a8e245b6704c4 (HEAD -> master, origin/master, origin/HEAD) Author: Frank Ch. Eigler <fche> Date: Wed Apr 19 11:23:16 2023 -0400 BZ2180328: disable pass-2 dyninst liveness analysis on CONFIG_RETPOLINE kernels As a stopgap measure, ameliorate the dramatic dyninst analysis time required to liveness-check $var assignments in kernels compiled with retpolines. Just skip the effort (with a warning). See also: https://github.com/dyninst/dyninst/issues/1305 . This should be fixed by the rebase of systemtap. The reproducer runs in a reasonable amount of time using a systemtap that includes that patch: $ sudo time stap -v -g fork.stp -c "./ssh.exp bz1028643 bbb" -o fork.stp.log Pass 1: parsed user script and 504 library scripts using 358256virt/153728res/16940shr/138804data kb, in 250usr/30sys/292real ms. WARNING: liveness analysis skipped on CONFIG_RETPOLINE kernel /usr/lib/debug/lib/modules/4.18.0-486.el8.x86_64/vmlinux: identifier '$return' at fork.stp:23:9 source: $return = -1 ^ Pass 2: analyzed script: 1 probe, 2 functions, 0 embeds, 0 globals using 424420virt/221316res/18092shr/204968data kb, in 960usr/80sys/1039real ms. Pass 3: using cached /root/.systemtap/cache/d0/stap_d0695e7c49ad338c333097e4c14796f6_1447.c Pass 4: using cached /root/.systemtap/cache/d0/stap_d0695e7c49ad338c333097e4c14796f6_1447.ko Pass 5: starting run. spawn ssh -o ConnectTimeout=10 bz1028643@localhost pwd Connection closed by ::1 port 22 Pass 5: run completed in 10usr/20sys/347real ms. 1.35user 0.15system 0:01.82elapsed 82%CPU (0avgtext+0avgdata 489836maxresident)k 0inputs+2776outputs (0major+58601minor)pagefaults 0swaps