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
