On Nov 19, 2011, at 10:50 PM, Ian Lance Taylor <iant@xxxxxxxxxx> wrote: > Matt <matt@xxxxxxx> writes: > >>> Great. I think that now we've cleared through the weeds and gotten to >>> the interesting part: why does it crash? I think the failing test is >>> gcc_AC_INITFINI_ARRAY in gcc/acinclude.m4. It is intended to see >>> whether the host linker correctly supports a mix of .init_array and >>> .ctors sections with priorities. This test is intended to be more or >>> less independent of the compiler, and is intended to only test the >>> linker. Both the host gcc used to build stage1 and the stage1 gcc >>> itself are presumably using the same linker (right?). So, why would the >>> test pass with the host gcc and fail with the stage1 gcc? >>> >>> If you can trace the points at which the static variable "count" >>> changes, that may help us pin down what is going wrong. >> >> Pin down, indeed :) When I try to watch or print 'count', I get this >> from GDB: >> Reading symbols from /home/matt/src/gcc-trunk/obj/conftest...done. >> (gdb) watch count >> Watchpoint 1: count >> (gdb) run >> Starting program: /home/matt/src/gcc-trunk/obj/conftest >> Error evaluating expression for watchpoint 1 >> value has been optimized out >> Watchpoint 1 deleted. >> >> So, it looks like an optimization bug of a sort to my naive eyes. >> >> If I take out the -flto=jobserver, the test no longer crashes and the >> variable is no longer optimized out incorrectly. Trying other -flto >> variants all elicited the original problem. When I tested compilation >> using the trunk *or* the system compiler (GCC 4.6.1-based) with -O2 >> -flto, I was able to repeat the problem exactly. >> >> Is this a wrong-code bug, and/or should that test never be compiled >> with -flto? > > That's interesting. Where did the -flto=jobserver option come from? > Did you add that? That commandline was pulled out of the config.log. My guess is that setting the profile to bootstrap-lto during configure does it. This might not have been seen before if no one tried using bootstrap-lto on a system where gold is the default system linker. > Looking at this, I think that this kind of test is going to fail when > using -flto and gold, because gold is going to report that the symbols > listed in the .ctors and .init_array sections are not visible from the > outside. Unfortunately this is not simple to fix in gold. In fact, I'm > not sure it's possible in the general case. Do we have enough info to file an actionable bug (or bugs)? if so, should I file it under the bootstrap component?
