3 ms·

> " In the above example, you may have noticed that a number &407eef was printed in place of a symbol. This is one of the tradeoffs that needed to be made by Co

> " In the above example, you may have noticed that a number &407eef was printed in place of a symbol. This is one of the tradeoffs that needed to be made by Cosmopolitan Libc's kprintf() function, which is too mission critical to be able to call into all the non-privileged code needed to open() + mmap() + etc. the concomitant ELF .com.dbg binary and load the symbol table. The simple solution for this is to have your main function call GetSymbolTable()" You could just log the base address of the executable and the relative addresses of the functions instead. The conversion from a relative address to the function's name can take place later, as part of a post-processing step. Should further reduce runtime overhead.

mikepurvis 4y ago
I think Tracealyzer does some of this kind of thing for logging embedded control flow in a way that's ultra compact but requires significant post processing after the trace has been recovered. It's a commercial product but in my usage/experience worth every penny: https://www.highintegritysystems.com/tools/tracealyzer/ https://www.highintegritysystems.com/tools/tracealyzer/
jart 4y ago
That's a smart way to do it and it certainly would have made things easier. I'm a big fan of the UNIX philosophy of small simple programs. But please consider that this facility is also used for ShowCrashReports() which prints a backtrace upon a SIGSEGV, SIGBUS, etc. When a crash spontaneously happens, it's not always easy or possible to run it again piped into an addr2line-like tool. It makes life simpler to have reporting facilities baked into each binary, and a lot of effort went into making it lightweight. Right now life.com (i.e. exit(42)) in the default build mode is 68kb (although it's 12kb in MODE=tiny) and that includes --ftrace, --strace, support for six operating systems and it embeds an operating system in each binary too, so it can run on autonomously on metal.
- Veserv 4y ago
  Why do you need to run the crashing program again? In the case you bring up you already printed the encoded backtrace. You can just copy the contents printed onto your screen/log file and post-process that as long as you have also output the relevant runtime linking information used to make the encoding.
- AlotOfReading 4y ago
  Is there a reason why you don't call GetSymbolTable() yourself in the runtime init or at least through an __attribute__((constructor)) if you want to keep it C?
  - jart 4y ago
    It's mostly to avoid imposing the latency on startup unless it's necessary or the user requested it. But now that you mention it, I think it should be updated to call that automatically in cases where the --strace flag is passed. Thanks!

mikepurvis 4y ago

I think Tracealyzer does some of this kind of thing for logging embedded control flow in a way that's ultra compact but requires significant post processing after the trace has been recovered. It's a commercial product but in my usage/experience worth every penny: https://www.highintegritysystems.com/tools/tracealyzer/ https://www.highintegritysystems.com/tools/tracealyzer/

jart 4y ago

That's a smart way to do it and it certainly would have made things easier. I'm a big fan of the UNIX philosophy of small simple programs. But please consider that this facility is also used for ShowCrashReports() which prints a backtrace upon a SIGSEGV, SIGBUS, etc. When a crash spontaneously happens, it's not always easy or possible to run it again piped into an addr2line-like tool. It makes life simpler to have reporting facilities baked into each binary, and a lot of effort went into making it lightweight. Right now life.com (i.e. exit(42)) in the default build mode is 68kb (although it's 12kb in MODE=tiny) and that includes --ftrace, --strace, support for six operating systems and it embeds an operating system in each binary too, so it can run on autonomously on metal.

Veserv 4y ago
Why do you need to run the crashing program again? In the case you bring up you already printed the encoded backtrace. You can just copy the contents printed onto your screen/log file and post-process that as long as you have also output the relevant runtime linking information used to make the encoding.
AlotOfReading 4y ago
Is there a reason why you don't call GetSymbolTable() yourself in the runtime init or at least through an __attribute__((constructor)) if you want to keep it C?
- jart 4y ago
  It's mostly to avoid imposing the latency on startup unless it's necessary or the user requested it. But now that you mention it, I think it should be updated to call that automatically in cases where the --strace flag is passed. Thanks!