linux-rng/kernel/trace/trace_probe.h, branch linus/master

tracing/probes: Treating longer symbol name on event comparation

2026-07-28T14:55:35Z

MAX_COMMON_HEAD_LEN (63) was used to allocate a temporary buffer for formatting command heads in trace_kprobe_match_command_head() and trace_uprobe_match_command_head(). However, the buffer size is too short for some longer symbols. Especially, with rust code, the symbol can be mangled and become very long. Refactor trace_kprobe_match_command_head() to perform direct string comparisons using strcmp() and strncmp(), eliminating the need for a temporary buffer and removing the MAX_COMMON_HEAD_LEN string length restriction on probe symbol names. For trace_uprobe_match_command_head(), since tu->filename is already matched via strncmp(), use a fixed 64-byte stack buffer solely for formatting offset and ref_ctr_offset (which requires at most 39 bytes). With all users converted, remove the MAX_COMMON_HEAD_LEN definition from trace_probe.h. Link: https://lore.kernel.org/all/178521361102.34226.9650586522488974115.stgit@devnote2/ Reported-by: Zhan Xusheng Link: https://lore.kernel.org/all/20260724023317.624074-1-zhanxusheng@xiaomi.com/ Signed-off-by: Masami Hiramatsu (Google)

tracing/probes: Remove redundant boolean conversion in trace_probe_has_single_file()

2026-07-21T08:59:42Z

list_is_singular() returns a boolean value, so the double negation (!!) in trace_probe_has_single_file() is redundant. Remove it. Link: https://lore.kernel.org/all/178454422826.296567.4382363406595169533.stgit@devnote2/ Assisted-by: Antigravity:gemini-3.5-flash Signed-off-by: Masami Hiramatsu (Google)

tracing/probes: Remove duplicate MAX_ARRAY_LEN macro definition

2026-07-21T08:59:39Z

MAX_ARRAY_LEN is defined twice in trace_probe.h. Remove the redundant definition. Link: https://lore.kernel.org/all/178454421926.296567.6649983666070787570.stgit@devnote2/ Assisted-by: Antigravity:gemini-3.5-flash Signed-off-by: Masami Hiramatsu (Google)

tracing/probes: Eliminate recursion in parse_probe_arg()

2026-07-14T13:43:40Z

To avoid potential stack overflows on limited kernel stacks, convert parse_probe_arg() from a recursive function into a loop-based implementation with a simple local state stack. Since recursion is eliminated using a loop with a fixed-size stack in the context, this restricts the dereference nesting depth. The maximum nesting depth of dereferences is now restricted to the same limit as typecasts (TRACEPROBE_MAX_NESTED_LEVEL, which is 8) and reports the same TOO_MANY_NESTED error. Update ftrace selftests to reflect this restriction and simplify the checks. Note that this change slightly alters the behavior of nested dereferencing in fetcharg. Previously, dereferencing without BTF allowed for up to 14 levels of nesting, whereas dereferencing with BTF was limited to 3 levels. With this change, the nesting depth is now limited to 8 levels in both cases. Link: https://lore.kernel.org/all/178399141396.27810.5390060618628718661.stgit@devnote2/ Assisted-by: Antigravity:gemini-3.5-flash Signed-off-by: Masami Hiramatsu (Google)

tracing/probes: Extend max length of argument string

2026-07-14T13:43:40Z

To support BTF argument parsing (such as accessing fields within nested structures via typecasting), the maximum argument string length needs to be extended. Extend MAX_ARGSTR_LEN from 63 to 255. Since MAX_ARGSTR_LEN was previously reused to format command heads in trace_*probe_match_command_head() functions, introduce a dedicated MAX_COMMON_HEAD_LEN (63) macro for matching command heads and switch these functions to use the new macro. Link: https://lore.kernel.org/all/178399140457.27810.11387684872148824707.stgit@devnote2/ Assisted-by: Antigravity:gemini-3.5-flash Signed-off-by: Masami Hiramatsu (Google)

tracing/probes: Sort ERRORS list in trace_probe.h alphabetically

2026-07-14T13:43:40Z

Sort the C-macro ERRORS list alphabetically in trace_probe.h to make it easier to find and maintain error entries. Link: https://lore.kernel.org/all/178399139516.27810.14930549550788208142.stgit@devnote2/ Assisted-by: Antigravity:gemini-3.5-flash Signed-off-by: Masami Hiramatsu (Google)

tracing/probes: Add this_cpu_read() and this_cpu_ptr() dereference method to fetcharg

2026-07-14T13:43:16Z

When tracing the kernel local variables, sometimes we need to get the CPU local variables. To access it, current simple dereference is not enough. Thus, introduce a special this_cpu_read() dereference to access per-cpu variable for the current CPU (accessing other CPU variable may race with updates on other CPUs). Also this_cpu_ptr() is for accessing per-cpu pointer. Those are working as same as the kernel percpu macro. Link: https://lore.kernel.org/all/178271367680.1176915.4711734074448973989.stgit@devnote2/ Signed-off-by: Masami Hiramatsu (Google)

tracing/probes: Add $current variable support

2026-07-14T13:43:16Z

Since we can use the BTF to cast value to a structure pointer type, it is useful to introduce "$current" special variable support to fetcharg. User can define a fetcharg to access current task_struct properties using BTF info. e.g. $current->cpus_ptr Link: https://lore.kernel.org/all/178271366709.1176915.15320906169981578568.stgit@devnote2/ Signed-off-by: Masami Hiramatsu (Google)

tracing/probes: Support field specifier option for typecast

2026-07-14T13:43:16Z

Add a field specifier option for the typecast. This works like container_of() macro. (STRUCT[,FIELD[.FIELD2...]])VAR This is equivalent to : container_of(VAR, struct STRUCT, FIELD[.FIELD2...]) For example: echo "f tick_nohz_handler next_tick=(tick_sched,sched_timer)timer->next_tick" >> dynamic_events This will trace tick_nohz_handler() with its tick_sched::next_tick which is converted from @timer by contianer_of(tick, struct tick_sched, sched_timer). So, if you enabkle both fprobes:tick_nohz_handler__entry and timer:hrtimer_expire_entry events, we will see something like: -0 [002] d.h1. 3778.087272: hrtimer_expire_entry: hrtimer=00000000d63db328 f unction=tick_nohz_handler now=3777450051040 -0 [002] d.h1. 3778.087281: tick_nohz_handler__entry: (tick_nohz_handler+0x4 /0x140) next_tick=3777450000000 Link: https://lore.kernel.org/all/178271365745.1176915.725923927180862257.stgit@devnote2/ Signed-off-by: Masami Hiramatsu (Google)

tracing/probes: Type casting always involves nested calls

2026-07-14T13:43:16Z

This allows type casting to various fetchargs without parentheses by recursively calling parse_probe_arg on the target when type casting is used. For example, this allows the following expressions: - (STRUCT)%REG->FIELD - (STRUCT)$stackN->FIELD - (STRUCT)@SYM->FIELD Note that @SYM+/-OFFSET with typecast needs parentheses like: - (STRUCT)(@SYM-8)->FIELD Link: https://lore.kernel.org/all/178271364804.1176915.17600229399446264813.stgit@devnote2/ Signed-off-by: Masami Hiramatsu (Google)