[RFC PATCH 6/7] tracing/probes: Support reserved this_cpu_ptr() method

[Masami Hiramatsu (Google)]

From: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>

The +PCPU() dereference operator was introduced in trace probes to
access a per-CPU pointer of a CPU local variable. However, kernel
developers are more familiar with the "this_cpu_ptr()" macro.

To make trace probe syntax more intuitive and aligned with standard
kernel macros, introduce support for "this_cpu_ptr(<fetcharg>)" as a
reserved method.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
---
 kernel/trace/trace.c       |    2 +-
 kernel/trace/trace_probe.c |    7 +++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 2b8c8ac4036a..60ab839d0867 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4332,7 +4332,7 @@ static const char readme_msg[] =
 	"\t           $stack<index>, $stack, $retval, $comm, $current\n"
 #endif
 	"\t           +|-[u]<offset>(<fetcharg>), \\imm-value, \\\"imm-string\"\n"
-	"\t           +CPU(<fetcharg>), +PCPU(<fetcharg>)\n"
+	"\t           +CPU(<fetcharg>), +PCPU(<fetcharg>), this_cpu_ptr(<fetcharg>)\n"
 	"\t     kernel return probes support: $retval, $arg<N>, $comm\n"
 	"\t     type: s8/16/32/64, u8/16/32/64, x8/16/32/64, char, string, symbol,\n"
 	"\t           b<bit-width>@<bit-offset>/<container-size>, ustring,\n"
diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index fa6757222fe6..27be0664cdf3 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -1315,6 +1315,7 @@ parse_probe_arg(char *arg, const struct fetch_type *type,
 		struct fetch_insn **pcode, struct fetch_insn *end,
 		struct traceprobe_parse_context *ctx)
 {
+	static const char *THIS_CPU_PTR_STR = "this_cpu_ptr(";
 	struct fetch_insn *code = *pcode;
 	unsigned long param;
 	int deref = FETCH_OP_DEREF;
@@ -1426,6 +1427,7 @@ parse_probe_arg(char *arg, const struct fetch_type *type,
 			ctx->offset += (tmp + 1 - arg) + (arg[0] != '-' ? 1 : 0);
 			arg = tmp + 1;
 		}
+handle_deref:
 		tmp = strrchr(arg, ')');
 		if (!tmp) {
 			trace_probe_log_err(ctx->offset + strlen(arg),
@@ -1476,6 +1478,11 @@ parse_probe_arg(char *arg, const struct fetch_type *type,
 		ret = handle_typecast(arg, pcode, end, ctx);
 		break;
 	default:
+		if (str_has_prefix(arg, THIS_CPU_PTR_STR)) {
+			arg += strlen(THIS_CPU_PTR_STR);
+			deref = FETCH_OP_CPU_PTR;
+			goto handle_deref;
+		}
 		if (isalpha(arg[0]) || arg[0] == '_') {	/* BTF variable */
 			if (!tparg_is_function_entry(ctx->flags) &&
 			    !tparg_is_function_return(ctx->flags)) {