On Thu, Jul 24, 2014 at 11:55 PM, Alexei Starovoitov <a...@kernel.org> wrote: > On Fri, Jul 25, 2014 at 10:25:03AM +0900, Michel Dänzer wrote: >> [ Adding the Debian kernel and gcc teams to Cc ] >> >> > movq $load_balance_mask, -136(%rbp) #, %sfp >> > subq $184, %rsp #, >> > >> > Anyway, this is not a kernel bug. This is your compiler creating >> > completely broken code. We may need to add a warning to make sure >> > nobody compiles with gcc-4.9.0, and the Debian people should probably >> > downgrate their shiny new compiler. >> >> Attached is fair.s from Debian gcc 4.8.3-5. Does that look better? I'm >> going to try reproducing the problem with a kernel built by that now. > > 4.8 and 4.7 don't hit the problem on this test. > 4.9 with -O2 compiles this file ok. 4.9 with -Os triggers it. > > -mno-red-zone only affected prologue emition in gcc. This part didn't > change between the releases. So the bug is quite deep. > What seems to be happening is that 2nd pass of instruction scheduler > (after emit prologue and reg alloc) is ignoring barrier properties > of 'subq $184, %rsp' and moving 'movq $.., -136(%rbp)' instruction > ahead of it. afaik rtl sched was never aware of 'red-zone'. > As an ex-compiler guy, I'm worried that this bug exists in earlier > releases. rtl backend guys need to take a serious look at it. > imo this is very serious bug, since broken red-zone is extremelly > hard to debug. > There are two weak test in gcc testsuite related to -mno-red-zone, > but not a single test that actually check that it is doing > the right thing. It is scary. I hope I'm wrong with this analysis. > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/
Alexi, Thanks for replying and sending this email to the Debian developers, seems to me a very serious issue with gcc. I don't known much about compilers but I trust your experience here. Nick -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
