• Steven Rostedt (VMware)'s avatar
    tracing: Make ftrace packed events have align of 1 · 4649079b
    Steven Rostedt (VMware) authored
    When using trace-cmd on 5.6-rt for the function graph tracer, the output was
    corrupted. It gave output like this:
    
     funcgraph_entry:       func=0xffffffff depth=38982
     funcgraph_entry:       func=0x1ffffffff depth=16044
     funcgraph_exit:        func=0xffffffff overrun=0x92539aaf00000000 calltime=0x92539c9900000072 rettime=0x100000072 depth=11084
     funcgraph_exit:        func=0xffffffff overrun=0x9253946e00000000 calltime=0x92539e2100000072 rettime=0x72 depth=26033702
     funcgraph_entry:       func=0xffffffff depth=85798
     funcgraph_entry:       func=0x1ffffffff depth=12044
    
    The reason was because the tracefs/events/ftrace/funcgraph_entry/exit format
    file was incorrect. The -rt kernel adds more common fields to the trace
    events. Namely, common_migrate_disable and common_preempt_lazy_count. Each
    is one byte in size. This changes the alignment of the normal payload. Most
    events are aligned normally, but the function and function graph events are
    defined with a "PACKED" macro, that packs their payload. As the offsets
    displayed in the format files are now calculated by an aligned field, the
    aligned field for function and function graph events should be 1, not their
    normal alignment.
    
    With aligning of the funcgraph_entry event, the format file has:
    
            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:unsigned char common_migrate_disable;     offset:8;       size:1; signed:0;
            field:unsigned char common_preempt_lazy_count;  offset:9;       size:1; signed:0;
    
            field:unsigned long func;       offset:16;      size:8; signed:0;
            field:int depth;        offset:24;      size:4; signed:1;
    
    But the actual alignment is:
    
    	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:unsigned char common_migrate_disable;	offset:8;	size:1;	signed:0;
    	field:unsigned char common_preempt_lazy_count;	offset:9;	size:1;	signed:0;
    
    	field:unsigned long func;	offset:12;	size:8;	signed:0;
    	field:int depth;	offset:20;	size:4;	signed:1;
    
    Link: https://lkml.kernel.org/r/20200609220041.2a3b527f@oasis.local.home
    
    Cc: stable@vger.kernel.org
    Fixes: 04ae87a5 ("ftrace: Rework event_create_dir()")
    Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
    4649079b
trace.h 65.6 KB