How to associate Elf with Dwfl_Module returned by dwfl_report_module

Milian Wolff mail@milianw.de
Sat Mar 17 13:15:00 GMT 2018


Hey there,

a recurring issue in the libdwfl integration of perf and perfparser are 
supposedly overlapping modules. The perf data file contains the exact mappings 
for all files corresponding to the actual mmap events that occurred during 
runtime, e.g.:

```
$ perf script --show-mmap-events | grep MMAP | grep stdc
heaptrack_print 13962 87163.483450: PERF_RECORD_MMAP2 13962/13962: 
[0x7fd0aea84000(0x387000) @ 0 08:03 413039 3864781083]: r-xp /usr/lib/libstdc+
+.so.6.0.24
heaptrack_print 13962 87163.483454: PERF_RECORD_MMAP2 13962/13962: 
[0x7fd0aebfc000(0x1ff000) @ 0x178000 08:03 413039 3864781083]: ---p /usr/lib/
libstdc++.so.6.0.24
heaptrack_print 13962 87163.483458: PERF_RECORD_MMAP2 13962/13962: 
[0x7fd0aedfb000(0xd000) @ 0x177000 08:03 413039 3864781083]: rw-p /usr/lib/
libstdc++.so.6.0.24
heaptrack_print 13962 87163.484860: PERF_RECORD_MMAP2 13962/13962: 
[0x7fd0aedfb000(0xc000) @ 0x177000 08:03 413039 3864781083]: r--p /usr/lib/
libstdc++.so.6.0.24
```
So far, both perf and perfparser are using dwfl_report_elf to report the file. 
But that API is deducing the mapping addresses internally, which may or may 
not be what we saw at runtime. I suspect that this is the reason for some 
issues we are seeing, such as supposedly overlapping modules. 

Looking at the Dwfl API, I cannot figure out how to feed the mapping directly. 
There's dwfl_report_module, but how would I associate an Elf* and int fd with 
it, as done by dwfl_report_elf?

Thanks
-- 
Milian Wolff
mail@milianw.de
http://milianw.de
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