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Re: gdb says EVERY argument or variable is optimized out (Re: gdb and fission scheme (gcc: -gsplit-dwarf, gnu ld gold :--gdb-index ))

On 2015/01/29 3:46, ISHIKAWA,chiaki wrote:
On 2015/01/26 17:48, Andrew Burgess wrote:
* ISHIKAWA,chiaki <> [2015-01-19 12:00:21 +0900]:

However, for debugging particular class of bugs,
I really needed to print some values on the stack trace when a
breakpoint is hit, as well as local variables manually.
So I made sure that I passed -O instead of higher optimization.

-O is not "no optimisation", do you get better debugging with -O0 ?

This might be it!
I will check and report next week.

Sorry for the noise.

With -O0, gdb session can print all the arguments and local variables (not that I checked EVERY variable, but it works like it should on a quick testing.)
So it is not gdb, GNU gold, or -gsplit-dwarf issue.
Funny, gcc 4.9 may do something extra in "-O" in comparison to older versions of gcc, and it seems that we have to suppress this new something by "-O0". I checked the heavily commented local test scripts and they mention only "-O" for quite a while. But the last time I did serious gdb session with mozilla software is at least a couple of years ago, so I can't say for sure.

Thank you again!


In my case, disabling -gsplit-dwarf means a very long time (several
minutes) of I/O during linking process alone and this is unacceptable
overhead for interactive debugging after changing a single C++
source file.

OK, but you could try it one time and see if it fixes your problem.
That would narrow down where the bug is coming from....

I will try it once also as well as -O0 above and report back.

with -gsplit-dwarf and -O0
without -gsplit-dwarf and {-O,-O0}

[Oh wait, I got a better symbol handling the year before, and I think
I used -O instead of -O0. Well, let me try anyway afresh and report back.]

Thank you for the hints!



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