On 2015.11.16 at 14:18 -0800, Steven Noonan wrote:
> Hi folks,
>
> (I'm not subscribed to the list, so please CC me on all responses.)
>
> This is using GCC 5.2 on Linux x86_64. On a project at work I've found
> that one of our shared libraries refuses to link because of some
> symbol references it shouldn't be making. If I add "-fno-devirtualize
> -fno-devirtualize-speculatively" to the compile flags, the issue goes
> away and everything links/runs fine. The issue does *not* appear on
> GCC 4.8 (which is used by our current production toolchain).
>
> First of all, does anyone have any ideas off the top of their head why
> devirtualization would break like this?
>
> Second, I'm looking for any ideas on how to gather meaningful data to
> submit a useful bug report for this issue. The best idea I've come up
> with so far is to preprocess one of the sources with the incorrect
> references and use 'delta' to reduce it to a minimal preprocessed
> source file that references one of these incorrect symbols.
> Unfortunately this is a sluggish process because such a minimal test
> case would need to compile correctly to an object file -- so "delta"
> is reducing it very slowly. So far I'm down from 11MB preprocessed
> source to 1.1MB preprocessed source after running delta a few times.
These undefined references are normally user errors. For example, when
you define an inline function, you need to link with the symbols it
uses.
markus@x4 /tmp % cat main.ii
struct A {
void foo();
};
struct B {
A v;
virtual void bar() { v.foo(); }
};
struct C {
B *w;
void Test() {
if (!w)
return;
while (1)
w->bar();
}
};
C a;
int main() { a.Test(); }
markus@x4 /tmp % g++ -fno-devirtualize -O2 -Wl,--no-undefined main.ii
markus@x4 /tmp % g++ -O2 -Wl,--no-undefined main.ii
/tmp/ccEvh2dL.o:main.ii:function B::bar(): error: undefined reference to
'A::foo()'
/tmp/ccEvh2dL.o:main.ii:function main: error: undefined reference to 'A::foo()'
collect2: error: ld returned 1 exit status
Instead of using delta you could try creduce instead. It is normally
much quicker:
https://github.com/csmith-project/creduce
--
Markus
