support stepping into the standard libarary

[jeremyschlatter]

godebug's current procedure for running instrumented code for a package x is:

• make a temp directory
• make a subdirectory $TMP/src/x containing instrumented versions of the source files for x
• run the go command, setting GOPATH=$TMP:$GOPATH. The go command finds our instrumented packages in $TMP/src and finds any other un-instrumented packages in the normal GOPATH.

That process does not work for standard library packages, though, because $GOROOT has to be a single directory.

Here's my current plan for working around this:

• Implement the proposal from #8 of having a permanent godebug directory that contains instrumented versions of all the packages we have seen so far. Put standard library packages in the same place, or possibly in their own /goroot or /std directory.
• From the same proposal, generate a temporary directory for every invocation of godebug and fill it with symlinks to the packages we want to instrument. The only new thing is that for all standard library packages we don't want to instrument, we will need to add a symlink to the real package in $GOROOT.

[pwaller]

Along these lines, I need to place a breakpoint in the standard library. I'm currently hitting net/http.ErrBodyReadAfterClose, and it's very difficult to tell why, so I want to set breakpoints in bufio and net/http, which I take it isn't possible or easy right now.

[jeffallen]

I just hit this problem, and I wasted a significant amount of time on it. :(

[jeremyschlatter]

@jeffallen sorry to hear that :( Is there some UX change we could make that would at least make it more obvious what was going on?

[jeffallen]

Well, it would be awesone if right before you stepped into non insrumented code it told you. Don't know if this is possible without too much overhead...

[jeremyschlatter]

Here's one idea: when the user runs "step", parse the next line and see if it contains a function call. Then run as normal until we hit the next godebug.Line call. If that call is in the same function as before -- we had no intervening godebug.EnterFunc or godebug.ExitFunc calls -- and we saw a function call in the code for the previous line, report to the user that it stepped over a function call, probably because the function was not instrumented.

[jeffallen]

+1
On Jun 21, 2015 7:24 AM, "Jeremy Schlatter" notifications@github.com
wrote:

Here's one idea: when the user runs "step", parse the next line and see if
it contains a function call. Then run as normal until we hit the next
godebug.Line call. If that call is in the same function as before -- we
had no intervening godebug.EnterFunc or godebug.ExitFunc calls -- and we
saw a function call in the code for the previous line, report to the user
that it stepped over a function call, probably because the function was not
instrumented.

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[andradei]

👍 Oh how much I wish for the std lib support

[doublerebel]

👍