The TP_printk() of a TRACE_EVENT() is a generic printf format that any developer can create for their event. It may include pointers to strings and such. A boot mapped buffer may contain data from a previous kernel where the strings addresses are different. One solution is to copy the event content and update the pointers by the recorded delta, but a simpler solution (for now) is to just use the print_fields() function to print these events. The print_fields() function just iterates the fields and prints them according to what type they are, and ignores the TP_printk() format from the event itself. To understand the difference, when printing via TP_printk() the output looks like this: 4582.696626: kmem_cache_alloc: call_site=getname_flags+0x47/0x1f0 ptr=00000000e70e10e0 bytes_req=4096 bytes_alloc=4096 gfp_flags=GFP_KERNEL node=-1 accounted=false 4582.696629: kmem_cache_alloc: call_site=alloc_empty_file+0x6b/0x110 ptr=0000000095808002 bytes_req=360 bytes_alloc=384 gfp_flags=GFP_KERNEL node=-1 accounted=false 4582.696630: kmem_cache_alloc: call_site=security_file_alloc+0x24/0x100 ptr=00000000576339c3 bytes_req=16 bytes_alloc=16 gfp_flags=GFP_KERNEL|__GFP_ZERO node=-1 accounted=false 4582.696653: kmem_cache_free: call_site=do_sys_openat2+0xa7/0xd0 ptr=00000000e70e10e0 name=names_cache But when printing via print_fields() (echo 1 > /sys/kernel/tracing/options/fields) the same event output looks like this: 4582.696626: kmem_cache_alloc: call_site=0xffffffff92d10d97 (-1831793257) ptr=0xffff9e0e8571e000 (-107689771147264) bytes_req=0x1000 (4096) bytes_alloc=0x1000 (4096) gfp_flags=0xcc0 (3264) node=0xffffffff (-1) accounted=(0) 4582.696629: kmem_cache_alloc: call_site=0xffffffff92d0250b (-1831852789) ptr=0xffff9e0e8577f800 (-107689770747904) bytes_req=0x168 (360) bytes_alloc=0x180 (384) gfp_flags=0xcc0 (3264) node=0xffffffff (-1) accounted=(0) 4582.696630: kmem_cache_alloc: call_site=0xffffffff92efca74 (-1829778828) ptr=0xffff9e0e8d35d3b0 (-107689640864848) bytes_req=0x10 (16) bytes_alloc=0x10 (16) gfp_flags=0xdc0 (3520) node=0xffffffff (-1) accounted=(0) 4582.696653: kmem_cache_free: call_site=0xffffffff92cfbea7 (-1831879001) ptr=0xffff9e0e8571e000 (-107689771147264) name=names_cache
Unified · Split
| @@ -4353,6 +4353,15 @@ static enum print_line_t print_trace_fmt(struct trace_iterator *iter) · 4352 unmodified lines | ||
| 4353 | 4353 | if (event) { |
| 4354 | 4354 | if (tr->trace_flags & TRACE_ITER_FIELDS) |
| 4355 | 4355 | return print_event_fields(iter, event); |
| 4356 | + /* | |
| 4357 | + * For TRACE_EVENT() events, the print_fmt is not | |
| 4358 | + * safe to use if the array has delta offsets | |
| 4359 | + * Force printing via the fields. | |
| 4360 | + */ | |
| 4361 | + if ((tr->text_delta || tr->data_delta) && | |
| 4362 | + event->type > __TRACE_LAST_TYPE) | |
| 4363 | + return print_event_fields(iter, event); | |
| 4364 | + | |
| 4356 | 4365 | return event->funcs->trace(iter, sym_flags, event); |
| 4357 | 4366 | } |
| 4358 | 4367 | |