The SystemTap team announces release 4.4 Enhancements to this release include: significant performance and stability improvements to user-space probing, implicit thread-local storage variables can now be accessed on x86_64, ppc and s390, support for processing floating point values, significantly improved concurrency for scripts using global variables via shortened critical sections, new syntax for defining aliases with both a prologue and epilogue, new @probewrite predicate and syscall arguments are writable again
= Where to get it https://sourceware.org/systemtap/ - our project page https://sourceware.org/systemtap/ftp/releases/ https://koji.fedoraproject.org/koji/packageinfo?packageID=615 git tag release-4.4 (commit 988f439af39a) There have been over 135 commits since the last release. There have been 25+ bugs fixed / features added since the last release. = SystemTap frontend (stap) changes - New syntax for defining aliases with both a prologue and an epilogue: 'probe ALIAS = PROBE { <prologue> }, { <epilogue> }' - New @probewrite predicate. @probewrite(var) returns 1 if var has been written to in the probe handler body and 0 otherwise. The check can only be used with probes that have an epilogue or prologue. - Implicit thread local storage variables can now be accessed on x86_64, ppc, and s390. = SystemTap backend changes - Various performance and stability improvements to user-space probing. This includes replacing spinlocks with RCU locks in vma map and utrace task's hash table lookups which reduces CPU time a lot when there are a lot of target processes and vma tracker or task finder is enabled. Also increased the default hash table sizes to reduce hash conflicts. Special thanks to Yichun Zhang and Sultan Alsawaf for these contributions. - The locks required to protect concurrent access to global variables has been optimized with a "pushdown" algorithm, so that they span the smallest possible critical region. Formerly, and with --compatible=4.3, locks always spanned the entire probe handler. Lock pushdown means much greater potential concurrency between probes running on different CPUs. - Systemtap now supports kernel-lockdown configurations that disable debugfs, by instead using procfs to carry relayfs transport files. = SystemTap tapset changes - Systemtap now supports extracting 64-bit floating point and stored in long type. Also basic floating point arithmetic and comparison functions are provided in a tapset. More automated syntax coming soon. e.g.: probe process.function("foo") { fp = user_long(& $fp_variable) println (fp_to_string (fp_add (string_to_fp("3.14"), fp))) } - Make syscall arguments writable again in non-DWARF probes on kernels that use syscall wrappers to pass arguments via pt_regs (currently x86_64 4.17+ and aarch64 4.19+). For example, the following probe adds rwx user permissions to any directory made by the process specified by stap -c: probe nd_syscall.mkdir { if (pid() == target()) mode |= 0700 } = SystemTap sample scripts - All 180+ examples can be found at https://sourceware.org/systemtap/examples/ - New sample scripts: floatingpoint.stp Extract a floating point value from a process and print the results of various simple floating point operations - The following sample scripts have been enabled to run on the stapbpf backend: general/sizeof.stp memory/overcommit.stp = Examples of tested kernel versions 2.6.32 (RHEL6 x86_64) 3.10.0 (RHEL7 x86_64) 4.15.0 (Ubuntu 18.04 x86_64) 4.18.0 (RHEL8 x86_64, aarch64, ppc64le, s390x) 5.3.8 (Fedora 30 i686) 5.8.16 (Fedora 32 x86_64) 5.8.18 (Fedora 33 x86_64) 5.9.0-rc7 (Fedora rawhide x86_64) 5.10.0-rc1 (Fedora rawhide x86_64) = Known issues with this release - There are known issues on kernel 5.10+ after adapting to set_fs() removal, with some memory accesses that previously returned valid data instead returning -EFAULT (see PR26811). - An sdt probe cannot parse a parameter that uses a segment register. (PR13429) - The presence of a line such as *CFLAGS += $(call cc-option, -fno-var-tracking-assignments) in the linux kernel Makefile unnecessarily reduces debuginfo quality, consider removing that line if you build kernels. = Contributors for this release Aaron Merey, Alice Zhang, Craig Ringer, Frank Ch. Eigler, Martin Cermak, Sagar Patel, Sergei Trofimovich*, Serhei Makarov, Stan Cox, Sultan Alsawaf*, Thorsten Glaser*, William Cohen, Yichun Zhang (agentzh) Special thanks to new contributors, marked with '*' above. Special thanks to Aaron Merey for drafting these notes. = Bugs fixed for this release <https://sourceware.org/PR#####> 10013 Support ENABLED sdt probe macro 12663 statement probes on inlined-function-call sites: search .debug_line PLUS .debug_info 13838 floating point $var support 14013 Access to user space thread local variables (errno) 14765 jvm crashes when specifying --runtime=dyninst 24954 stapdyn on ppc/aarch64 do not support full register set 25549 Systemtap unable to find many probe points available in code compiled with LTO enable 26015 make syscall arguments symbol-writeable again 26123 Use of VMA tracker would leak kernel slab memory for modern kernels without CONFIG_UTRACE 26131 Relay flushing results in garbled output data being read by staprun 26142 Kernel module compilation fails for the latest Fedora Rawhide x64 26181 tapset/linux/nfs_proc.stp needs update 26249 uconversions format error: format ‘%lx’ expects argument of type ‘long unsigned int’, but argument 5 has type ‘void *’ 26296 delay script-global locking until required 26307 kernel commit ed66f991bb19 breaks module initialization 26379 stap -p4 systemtap.examples/network/nfsd-trace.stp fails 26392 The optimizer would generate inefficient code which always evaluate dwarf ops eagerly 26511 PR18115 + PR11353 + PR26296 = build error 26567 systemtap-mode uses obsolete common lisp emulation 26658 restore onboot capability via /usr/bin/kernel-install 26660 probe kernel.statement(HEX).absolute incorrectly requires kernel debuginfo 26665 secureboot stap-server matching breaks if non-stap MOK is already enrolled 26673 The kernel backtrace dumper should not use stack array which may lead to compilation errors 26697 NULL pointer dereference might happen in get_utrace_lock() 26846 task_finder2: kernel panics by due to unreliable in_atomic() usage
