This is the implementation of parsing the .sframe section in an ELF file. It's a continuation of Josh's and Steve's work that can be found here:
https://lore.kernel.org/all/[email protected]/ https://lore.kernel.org/all/[email protected]/ Currently the only way to get a user space stack trace from a stack walk (and not just copying large amount of user stack into the kernel ring buffer) is to use frame pointers. This has a few issues. The biggest one is that compiling frame pointers into every application and library has been shown to cause performance overhead. Another issue is that the format of the frames may not always be consistent between different compilers and some architectures (s390) has no defined format to do a reliable stack walk. The only way to perform user space profiling on these architectures is to copy the user stack into the kernel buffer. SFrame [1] is now supported in binutils (x86-64, ARM64, and s390). There is discussions going on about supporting SFrame in LLVM. SFrame acts more like ORC, and lives in the ELF executable file as its own section. Like ORC it has two tables where the first table is sorted by instruction pointers (IP) and using the current IP and finding it's entry in the first table, it will take you to the second table which will tell you where the return address of the current function is located and then you can use that address to look it up in the first table to find the return address of that function, and so on. This performs a user space stack walk. Now because the .sframe section lives in the ELF file it needs to be faulted into memory when it is used. This means that walking the user space stack requires being in a faultable context. As profilers like perf request a stack trace in interrupt or NMI context, it cannot do the walking when it is requested. Instead it must be deferred until it is safe to fault in user space. One place this is known to be safe is when the task is about to return back to user space. This series makes the deferred unwind user code implement SFrame format V2 with the latest format enhancements (i.e. PC-relative SFrame FDE function start address, represent return address undefined) and enables it on x86-64. [1]: https://sourceware.org/binutils/wiki/sframe This series applies on top of Peter Zijlstras latest unwind user enhancements and perf deferred callchain support on his tip perf/core branch which has been merged to the tip master branch (f8fdee44bf2f): git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git master with Namhyung Kim's related latest perf tools deferred callchain support merged on top (if you want to use "perf record --call-graph fp,defer" and "perf report/script" for testing): git://git.kernel.org/pub/scm/linux/kernel/git/namhyung/linux-perf.git perf/defer-callchain-v4 The to be stack-traced user space programs (and libraries) need to be built with the latest SFrame stack trace information format V2, with the recent PC-relative SFrame FDE function start address encoding and optionally the support to represent return address undefined, as generated by binutils 2.45+ with assembler option --gsframe. Changes since v11 (see patch notes for details): - Rebase on tip master branch (f8fdee44bf2f) with Namhyung Kim's perf/defer-callchain-v4 branch merged on top. - Adjust to Peter's latest undwind user enhancements. - Simplify logic by using an internal SFrame FDE representation, whose FDE function start address field is an address instead of a PC-relative offset (from FDE). - Rename struct sframe_fre to sframe_fre_internal to align with struct sframe_fde_internal. - Remove unused pt_regs from unwind_user_next_common() and its callers. (Peter) - Simplify unwind_user_next_sframe(). (Peter) - Fix a few checkpatch errors and warnings. - Minor cleanups (e.g. move includes, fix indentation). Changes since v10: - Support for SFrame V2 PC-relative FDE function start address. - Support for SFrame V2 representing RA undefined as indication for outermost frames. Patches 1, 4, and 12 have been updated to exclusively support the recent PC-relative SFrame FDE function start address encoding. With binutils 2.45 the SFrame V2 FDE function start address field value is an offset from the field (i.e. PC-relative) instead of from the .sframe section start. This is indicated by the new SFrame header flag SFRAME_F_FDE_FUNC_START_PCREL. Old SFrame V2 sections get rejected with dynamic debug message "bad/unsupported sframe header". Patches 7 and 8 add support to unwind user and unwind user sframe for a recent change of the SFrame V2 format to represent an undefined return address as an SFrame FRE without any offsets, which is used as indication for outermost frames. Note that currently only a development build of binutils mainline generates SFrame information including this new indication for outermost frames. SFrame information without the new indication is still supported. Without these patches unwind user sframe would identify such new SFrame FREs without any offsets as corrupted and would therefore remove the .sframe section, causing any any further stack tracing using sframe to fail. Regards, Jens Jens Remus (2): unwind_user: Stop when reaching an outermost frame unwind_user/sframe: Add support for outermost frame indication Josh Poimboeuf (11): unwind_user/sframe: Add support for reading .sframe headers unwind_user/sframe: Store .sframe section data in per-mm maple tree x86/uaccess: Add unsafe_copy_from_user() implementation unwind_user/sframe: Add support for reading .sframe contents unwind_user/sframe: Detect .sframe sections in executables unwind_user/sframe: Wire up unwind_user to sframe unwind_user/sframe/x86: Enable sframe unwinding on x86 unwind_user/sframe: Remove .sframe section on detected corruption unwind_user/sframe: Show file name in debug output unwind_user/sframe: Add .sframe validation option unwind_user/sframe: Add prctl() interface for registering .sframe sections MAINTAINERS | 1 + arch/Kconfig | 23 ++ arch/x86/Kconfig | 1 + arch/x86/include/asm/mmu.h | 2 +- arch/x86/include/asm/uaccess.h | 39 +- arch/x86/include/asm/unwind_user.h | 6 +- fs/binfmt_elf.c | 48 ++- include/linux/mm_types.h | 3 + include/linux/sframe.h | 60 +++ include/linux/unwind_user_types.h | 5 +- include/uapi/linux/elf.h | 1 + include/uapi/linux/prctl.h | 6 +- kernel/fork.c | 10 + kernel/sys.c | 9 + kernel/unwind/Makefile | 3 +- kernel/unwind/sframe.c | 627 +++++++++++++++++++++++++++++ kernel/unwind/sframe.h | 72 ++++ kernel/unwind/sframe_debug.h | 68 ++++ kernel/unwind/user.c | 29 ++ mm/init-mm.c | 2 + 20 files changed, 996 insertions(+), 19 deletions(-) create mode 100644 include/linux/sframe.h create mode 100644 kernel/unwind/sframe.c create mode 100644 kernel/unwind/sframe.h create mode 100644 kernel/unwind/sframe_debug.h -- 2.48.1
