Re: RFR(M): 8247515: OSX pc_to_symbol() lookup does not work with core files

[serguei.spit...@oracle.com]

Hi Chris,

I like the suggestion from Kevin below.

I have a couple of minor comments so far.

http://cr.openjdk.java.net/~cjplummer/8247515/webrev.01/src/jdk.hotspot.agent/macosx/native/libsaproc/libproc_impl.c.frames.html

 313       if (!lib->next || lib->next->base >= addr) {

I wonder if the check above has to be:

 313       if (!lib->next || lib->next->base > addr) {

http://cr.openjdk.java.net/~cjplummer/8247515/webrev.01/src/jdk.hotspot.agent/macosx/native/libsaproc/symtab.c.frames.html

 417       if (offset_from_sym >= 0) { // ignore symbols that comes after "offset"

Replace: comes => come

Thanks,
Serguei


On 7/8/20 03:23, Kevin Walls wrote:

Sure -- I was thinking lowest_offset_from_sym initialising starting at a high positive integer (that would now be PTRDIFF_MAX I think) to save a comparison with e.g. -1, you can just check if the new offset is less than lowest_offset_from_sym

With the ptrdiff_t change you made, this all looks good to me however you decide. 8-)

On 07/07/2020 21:17, Chris Plummer wrote:

Hi Kevin,

Thanks for the review. Yes, that lack of initialization of lowest_offset_from_sym is a bug. I'm real surprised the compiler didn't catch it as it will be uninitialized garbage the first time it is referenced. Fortunately usually the eventual offset is very small if not 0, so probably this never prevented a proper match. I think there's also another bug:

 415       uintptr_t offset_from_sym = offset - sym->offset;

"offset" is the passed in offset, essentially the address of the symbol we are interested in, but given as an offset from the start of the DSO. "sym->offset" is also an offset from the start of the DSO. It could be located before or after "offset". This means the math could result in a negative number, which when converted to unsigned would be a very large positive number. This happens whenever you check a symbol that is actually located after the address you are looking up. The end result is harmless, because it just means there's no way we will match that symbol, which is what you want, but it would be good to clean this up.

I think what is best is to use ptrdiff_t and initialize lowest_offset_from_sym to -1. I've updated the webrev:

http://cr.openjdk.java.net/~cjplummer/8247515/webrev.01/index.html

thanks,

Chris

On 7/7/20 4:09 AM, Kevin Walls wrote:

Hi Chris,

Yes I think this looks good.

Question: In nearest_symbol, do we need to initialize lowest_offset_from_sym to something impossibly high, as if it defaults to zero we never find a better/nearer result?

Thanks
Kevin


On 07/07/2020 06:10, Chris Plummer wrote:

Hello,

Please help review the following:

http://cr.openjdk.java.net/~cjplummer/8247515/webrev.00/index.html
https://bugs.openjdk.java.net/browse/JDK-8247515

The CR contains a description of the issues being addressed. There is also no test for this symbol lookup support yet. It will be there after I push JDK-8247516 and  JDK-8247514, which are both blocked by the CR.

[1] https://bugs.openjdk.java.net/browse/JDK-8247516
[2] https://bugs.openjdk.java.net/browse/JDK-8247514

thanks,

Chris