Question about build mode: release/debug/optdebug

[Sunghyun Park]

Hi, all.

I'm trying to count the number of dynamic instructions for jitted code in V8 by using PIN. 

Since PIN leverages symbol table to identify jitted code, I needed to compile V8 with debug mode to provide information for the symbol table. 

However, I'm not sure whether debug mode applies the same level of optimization as release mode. 

I spent some time searching, but I couldn't find any useful information. 

Is there anyone who can clarify the difference between release/debug/optdebug in V8?

Any advice would be greatly helpful.

Thank you!

[Jakob Kummerow]

It's complicated and for the details, you'll have to look at build configuration files (start with BUILD.gn and gni/v8.gni, if needed continue with generated .ninja files in the output directory), but the short answer is that the three build modes affect C++ compilation as follows:

release: -O3

debug: -O0 -DDEBUG

optdebug: -O2 -DDEBUG

Additionally, there is a flag --debug-code that controls whether extra checks are emitted in generated code. It is on by default in when DEBUG is defined, and off by default otherwise, but can be overridden.

So for your purposes, you probably want an optdebug build and the --nodebug-code command-line flag.

Please double-check everything I've said here before blindly trusting any results.

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