I want to profile code that is jitted at runtime. Specifically i
want to profile code generated by mono. (a .NET runtime)
The generated code of course has no debug symbols, so I'd like to
write some kind of plugin or extension that will let Shark translate
function address to human readable symbols.
Shark provides no infrastructure for this. JIT code isn't listed as a
header by the dynamic linker so Shark doesn't even know where to look
for symbol information. The profile will show the addresses of the
executed JIT code, but there are a few potential problems. If the JIT
doesn't preserve the frame pointer, the backtrace will be useless
after the top frame. Even with that in place, Shark collects symbol
information at the end of the sampling. This is to avoid the
performance impact of doing symbol lookups during the sampling. If
the JIT reuses the same block of memory for multiple JIT fragments,
then Shark has no idea which code fragment was JIT'd to a given
address when the sample was recorded. The JIT would need to keep
track of every JIT code fragment generated, the original source it
came from, and when the code fragment was generated.
I saw that there is a Chud - Symbolification framework, so i am
wondering if there are some hooks I can implement to generate
symbols for the generated code. I can very easily add some functions
that will return a symbol, based on a the function adress.
CHUDSymbolication.framework is an internal framework. No
documentation or headers are provided and the interface is subject to
change. Even with that notice, I should point out that it doesn't
offer the type of functionality you want anyway.
Any ideas? Is this possible at all? is there any information on the
Chud Symbolification framework out there?
The only way this would be possible would be to either:
- Have a code cache that never evicts. Provide a function to map from
JIT address to source address/information. Have us add support for
calling that function to Shark.
- Have a code cache that evicts. Keep a log of all code fragments
generated, the JIT address, the source address/information, and the
time the code fragment was JIT'd. Provide a description of the log
format. Have us add support for that log format to Shark.
Best regards,
Joachim Ante
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Rick Altherr
Architecture and Performance Group
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