Re: GCC strcmp optimizations causing valgrind uninitialized conditional jumps

Is there a bug tracking the issue? Also, unless your malloc is
guaranteed to be zeroing out the data or have a strcmp that is writing
doubleworld aligned data to the string, the strcmp implementation is
branching based on data existing after the null terminating character
that may be uninitialized. Both sides of the branch do the right thing
though, and locate the null terminator, throwing away the calculations
done on the uninitialized data.

-fno-builtin-strcmp or -mstring-compare-inline-limit=0 do work fine
but we don't control the binaries we are linking against in all cases
and are seeing the issue pop up there.
On Tue, Jul 3, 2018 at 11:46 AM Segher Boessenkool
[off-list ref] wrote:

Hi!

On Tue, Jul 03, 2018 at 11:26:55AM -0700, William Kennington wrote:

quoted

I've noticed while trying to do some valgrind testing on code linked
against system libraries that have inlined strcmps that valgrind is
unhappy about branches depending on uninitialized memory. I've read

The branches here do *not* depend on uninitialised memory.  Valgrind
does not realise that however.  The valgrind people are aware of this
problem.

quoted

Any ideas on how to workaround / fix this?

Does -fno-builtin-strcmp do the trick?


Segher