[PATCH 1/2] tracing: Handle "(const) char __attribute() *" as string ptr type

[Masami Hiramatsu (Google)]

From: Masami Hiramatsu (Google) <mhira...@kernel.org>

With CONFIG_DEBUG_INFO_BTF=y and PAHOLE_HAS_BTF_TAG=y, `__user` is
converted to `__attribute((btf_type_tag("user")))`. In this case,
some syscall events have `const char __attribute(...) *` for __user
string, like below;

/sys/kernel/tracing # cat events/syscalls/sys_enter_openat/format
name: sys_enter_openat
ID: 720
format:
        field:unsigned short common_type;       offset:0;       size:2; 
signed:0;
        field:unsigned char common_flags;       offset:2;       size:1; 
signed:0;
        field:unsigned char common_preempt_count;       offset:3;       size:1; 
signed:0;
        field:int common_pid;   offset:4;       size:4; signed:1;

        field:int __syscall_nr; offset:8;       size:4; signed:1;
        field:int dfd;  offset:16;      size:8; signed:0;
        field:const char __attribute__((btf_type_tag("user"))) * filename;      
offset:24;      size:8; signed:0;
        field:int flags;        offset:32;      size:8; signed:0;
        field:umode_t mode;     offset:40;      size:8; signed:0;


Then the trace event filter failes to set string acceptable flag
(FILTER_PTR_STRING) and rejects setting string filter;

# echo 'filename.ustring ~ "*ftracetest-dir.wbx24v*"' >> 
events/syscalls/sys_enter_openat/filter
sh: write error: Invalid argument
 # cat error_log
[  723.743637] event filter parse error: error: Expecting numeric field
  Command: filename.ustring ~ "*ftracetest-dir.wbx24v*"

Handle "(const) char __attribute() *" also as string ptr type.

Signed-off-by: Masami Hiramatsu (Google) <mhira...@kernel.org>
---
 kernel/trace/trace_events_filter.c |    5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/trace/trace_events_filter.c 
b/kernel/trace/trace_events_filter.c
index 3885aadc434d..5e27190a0377 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -1488,6 +1488,11 @@ int filter_assign_type(const char *type)
        if (strcmp(type, "char *") == 0 || strcmp(type, "const char *") == 0)
                return FILTER_PTR_STRING;
 
+       /* Ignore attributes */
+       if (glob_match("char __attribute(*) \\*", type) ||
+           glob_match("const char __attribute(*) \\*", type))
+               return FILTER_PTR_STRING;
+
        return FILTER_OTHER;
 }