From: Masami Hiramatsu (Google) <[email protected]> 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 Signed-off-by: Masami Hiramatsu (Google) <[email protected]> --- Changes in v8: - Avoid uninitialized ctx->btf issue on $current without typecast. Changes in v7: - Fix to use force-typecast for task_struct implicitly. Changes in v6: - Rebased on dump fetcharg patch. - Remove function name/eprobe requirement for $current. Changes in v5: - Use s32 for bof_find_btf_id(). Changes in v4: - Add $current in README when CONFIG_HAVE_FUNCTION_ARG_ACCESS_API=y case. - Fix to prohibit using $current in eprobes and address based kprobes. Changes in v3: - Remove $current support from eprobes (because eprobes is only for event) - Prohibit uprobes to use $current. Changes in v2: - Support to parse $current in parse_btf_arg(). - If no typecast on $current, it automatically casted to task_struct. - Check error case if $current follows something except for "-". --- Documentation/trace/fprobetrace.rst | 1 + Documentation/trace/kprobetrace.rst | 1 + kernel/trace/trace.c | 4 ++-- kernel/trace/trace_probe.c | 37 ++++++++++++++++++++++++++++++++++- kernel/trace/trace_probe.h | 1 + kernel/trace/trace_probe_tmpl.h | 3 +++ 6 files changed, 44 insertions(+), 3 deletions(-) diff --git a/Documentation/trace/fprobetrace.rst b/Documentation/trace/fprobetrace.rst index 290a9e6f7491..3392cab016b3 100644 --- a/Documentation/trace/fprobetrace.rst +++ b/Documentation/trace/fprobetrace.rst @@ -50,6 +50,7 @@ Synopsis of fprobe-events $argN : Fetch the Nth function argument. (N >= 1) (\*2) $retval : Fetch return value.(\*3) $comm : Fetch current task comm. + $current : Fetch the address of the current task_struct. +|-[u]OFFS(FETCHARG) : Fetch memory at FETCHARG +|- OFFS address.(\*4)(\*5) \IMM : Store an immediate value to the argument. NAME=FETCHARG : Set NAME as the argument name of FETCHARG. diff --git a/Documentation/trace/kprobetrace.rst b/Documentation/trace/kprobetrace.rst index a62707e6a9f2..81e4fe38791d 100644 --- a/Documentation/trace/kprobetrace.rst +++ b/Documentation/trace/kprobetrace.rst @@ -53,6 +53,7 @@ Synopsis of kprobe_events $argN : Fetch the Nth function argument. (N >= 1) (\*1) $retval : Fetch return value.(\*2) $comm : Fetch current task comm. + $current : Fetch the address of the current task_struct. +|-[u]OFFS(FETCHARG) : Fetch memory at FETCHARG +|- OFFS address.(\*3)(\*4) \IMM : Store an immediate value to the argument. NAME=FETCHARG : Set NAME as the argument name of FETCHARG. diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 0e36af853199..7a5676524f1a 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -4323,13 +4323,13 @@ static const char readme_msg[] = "\t args: <name>=fetcharg[:type]\n" "\t fetcharg: (%<register>|$<efield>), @<address>, @<symbol>[+|-<offset>],\n" #ifdef CONFIG_HAVE_FUNCTION_ARG_ACCESS_API - "\t $stack<index>, $stack, $retval, $comm, $arg<N>,\n" + "\t $stack<index>, $stack, $retval, $comm, $arg<N>, $current\n" #ifdef CONFIG_PROBE_EVENTS_BTF_ARGS "\t [(structname[,field])]<argname>[->field[->field|.field...]],\n" "\t [(structname[,field])](fetcharg)->field[->field|.field...],\n" #endif #else - "\t $stack<index>, $stack, $retval, $comm,\n" + "\t $stack<index>, $stack, $retval, $comm, $current\n" #endif "\t +|-[u]<offset>(<fetcharg>), \\imm-value, \\\"imm-string\"\n" "\t kernel return probes support: $retval, $arg<N>, $comm\n" diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c index 2d5b2686cc15..eb58b70ae082 100644 --- a/kernel/trace/trace_probe.c +++ b/kernel/trace/trace_probe.c @@ -692,7 +692,9 @@ static int parse_btf_arg(char *varname, int i, is_ptr, ret; u32 tid; - if (!ctx->funcname && !(ctx->flags & TPARG_FL_TEVENT)) + /* Note: field is not separated at this point, so check prefix. */ + if (!str_has_prefix(varname, "$current") && + !ctx->funcname && !(ctx->flags & TPARG_FL_TEVENT)) return -EINVAL; is_ptr = split_next_field(varname, &field, ctx); @@ -705,6 +707,20 @@ static int parse_btf_arg(char *varname, return -EOPNOTSUPP; } + if (!strcmp(varname, "$current")) { + code->op = FETCH_OP_CURRENT; + /* If no typecast is specified for $current, use task_struct by default */ + ret = bpf_find_btf_id("task_struct", BTF_KIND_STRUCT, &ctx->struct_btf); + if (ret < 0) { + trace_probe_log_err(ctx->offset, NO_BTF_ENTRY); + return -ENOENT; + } + tid = (u32)ret; + type = ctx->last_struct = + btf_type_skip_modifiers(ctx->struct_btf, tid, NULL); + goto found_type; + } + if (ctx->flags & TPARG_FL_RETURN && !strcmp(varname, "$retval")) { code->op = FETCH_OP_RETVAL; /* Check whether the function return type is not void, even with typecast. */ @@ -761,6 +777,7 @@ static int parse_btf_arg(char *varname, found: type = btf_type_skip_modifiers(ctx->btf, tid, NULL); +found_type: if (!type) { trace_probe_log_err(ctx->offset, BAD_BTF_TID); return -EINVAL; @@ -1270,6 +1287,24 @@ static int parse_probe_vars(char *orig_arg, const struct fetch_type *t, return 0; } + /* $current returns the address of the current task_struct. */ + if (str_has_prefix(arg, "current")) { + /* $current is only supported by kernel probe. */ + if (!(ctx->flags & TPARG_FL_KERNEL)) { + err = TP_ERR_BAD_VAR; + goto inval; + } + arg += strlen("current"); + if (*arg == '-' && IS_ENABLED(CONFIG_PROBE_EVENTS_BTF_ARGS)) + return parse_btf_arg(orig_arg, pcode, end, ctx); + + if (*arg != '\0') + goto inval; + + code->op = FETCH_OP_CURRENT; + return 0; + } + #ifdef CONFIG_HAVE_FUNCTION_ARG_ACCESS_API len = str_has_prefix(arg, "arg"); if (len) { diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h index e7fcc77f51fc..053f72fdaece 100644 --- a/kernel/trace/trace_probe.h +++ b/kernel/trace/trace_probe.h @@ -92,6 +92,7 @@ typedef int (*print_type_func_t)(struct trace_seq *, void *, void *); FETCH_OP(RETVAL, none), /* Return value */ \ FETCH_OP(IMM, imm), /* Immediate: .immediate */ \ FETCH_OP(COMM, none), /* Current comm */ \ + FETCH_OP(CURRENT, none), /* Current task_struct address */\ FETCH_OP(ARG, param), /* Argument: .param = index */ \ FETCH_OP(FOFFS, imm), /* File offset: .immediate */ \ FETCH_OP(IMMSTR, string), /* Allocated string: .data */ \ diff --git a/kernel/trace/trace_probe_tmpl.h b/kernel/trace/trace_probe_tmpl.h index 51436f19083b..d0e9662cde00 100644 --- a/kernel/trace/trace_probe_tmpl.h +++ b/kernel/trace/trace_probe_tmpl.h @@ -112,6 +112,9 @@ process_common_fetch_insn(struct fetch_insn *code, unsigned long *val) case FETCH_OP_IMMSTR: *val = (unsigned long)code->data; break; + case FETCH_OP_CURRENT: + *val = (unsigned long)current; + break; default: return -EILSEQ; }
