From 105f75ebf9519c239c96f9b16e16520f45fea72b Mon Sep 17 00:00:00 2001 From: Jianlin Lv Date: Wed, 10 Feb 2021 14:26:46 +0800 Subject: [PATCH] perf probe: Fix kretprobe issue caused by GCC bug Perf failed to add a kretprobe event with debuginfo of vmlinux which is compiled by gcc with -fpatchable-function-entry option enabled. The same issue with kernel module. Issue: # perf probe -v 'kernel_clone%return $retval' ...... Writing event: r:probe/kernel_clone__return _text+599624 $retval Failed to write event: Invalid argument Error: Failed to add events. Reason: Invalid argument (Code: -22) # cat /sys/kernel/debug/tracing/error_log [156.75] trace_kprobe: error: Retprobe address must be an function entry Command: r:probe/kernel_clone__return _text+599624 $retval ^ # llvm-dwarfdump vmlinux |grep -A 10 -w 0x00df2c2b 0x00df2c2b: DW_TAG_subprogram DW_AT_external (true) DW_AT_name ("kernel_clone") DW_AT_decl_file ("/home/code/linux-next/kernel/fork.c") DW_AT_decl_line (2423) DW_AT_decl_column (0x07) DW_AT_prototyped (true) DW_AT_type (0x00dcd492 "pid_t") DW_AT_low_pc (0xffff800010092648) DW_AT_high_pc (0xffff800010092b9c) DW_AT_frame_base (DW_OP_call_frame_cfa) # cat /proc/kallsyms |grep kernel_clone ffff800010092640 T kernel_clone # readelf -s vmlinux |grep -i kernel_clone 183173: ffff800010092640 1372 FUNC GLOBAL DEFAULT 2 kernel_clone # objdump -d vmlinux |grep -A 10 -w \: ffff800010092640 : ffff800010092640: d503201f nop ffff800010092644: d503201f nop ffff800010092648: d503233f paciasp ffff80001009264c: a9b87bfd stp x29, x30, [sp, #-128]! ffff800010092650: 910003fd mov x29, sp ffff800010092654: a90153f3 stp x19, x20, [sp, #16] The entry address of kernel_clone converted by debuginfo is _text+599624 (0x92648), which is consistent with the value of DW_AT_low_pc attribute. But the symbolic address of kernel_clone from /proc/kallsyms is ffff800010092640. This issue is found on arm64, -fpatchable-function-entry=2 is enabled when CONFIG_DYNAMIC_FTRACE_WITH_REGS=y; Just as objdump displayed the assembler contents of kernel_clone, GCC generate 2 NOPs at the beginning of each function. kprobe_on_func_entry detects that (_text+599624) is not the entry address of the function, which leads to the failure of adding kretprobe event. kprobe_on_func_entry ->_kprobe_addr ->kallsyms_lookup_size_offset ->arch_kprobe_on_func_entry // FALSE The cause of the issue is that the first instruction in the compile unit indicated by DW_AT_low_pc does not include NOPs. This issue exists in all gcc versions that support -fpatchable-function-entry option. I have reported it to the GCC community: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98776 Currently arm64 and PA-RISC may enable fpatchable-function-entry option. The kernel compiled with clang does not have this issue. FIX: This GCC issue only cause the registration failure of the kretprobe event which doesn't need debuginfo. So, stop using debuginfo for retprobe. map will be used to query the probe function address. Signed-off-by: Jianlin Lv Acked-by: Masami Hiramatsu Cc: Alexander Shishkin Cc: clang-built-linux@googlegroups.com Cc: Frank Ch. Eigler Cc: Ian Rogers Cc: Jiri Olsa Cc: Mark Rutland Cc: Namhyung Kim Cc: Nathan Chancellor Cc: Nick Desaulniers Cc: Peter Zijlstra Cc: Sumanth Korikkar Link: http://lore.kernel.org/lkml/20210210062646.2377995-1-Jianlin.Lv@arm.com Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/util/probe-event.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c index 8eae2aff..a59d326 100644 --- a/tools/perf/util/probe-event.c +++ b/tools/perf/util/probe-event.c @@ -894,6 +894,16 @@ static int try_to_find_probe_trace_events(struct perf_probe_event *pev, struct debuginfo *dinfo; int ntevs, ret = 0; + /* Workaround for gcc #98776 issue. + * Perf failed to add kretprobe event with debuginfo of vmlinux which is + * compiled by gcc with -fpatchable-function-entry option enabled. The + * same issue with kernel module. The retprobe doesn`t need debuginfo. + * This workaround solution use map to query the probe function address + * for retprobe event. + */ + if (pev->point.retprobe) + return 0; + dinfo = open_debuginfo(pev->target, pev->nsi, !need_dwarf); if (!dinfo) { if (need_dwarf) -- 2.7.4