Date: Fri, 5 May 2017 22:13:12 -0700 From: Mark Millard <markmi@dsl-only.net> To: FreeBSD Toolchain <freebsd-toolchain@freebsd.org>, FreeBSD PowerPC ML <freebsd-ppc@freebsd.org> Subject: Re: llvm FreeBSD powerpc ABI target bug fix: Re: [Bug 26519] Clang 4.0.0's "Target: powerpc-unknown-freebsd11.0" code generation is violating the SVR4 ABI (SEGV can result) Message-ID: <C9CB8645-472E-40D9-B193-E977F842C37B@dsl-only.net> In-Reply-To: <E177E5EE-25EB-4CBA-9C0F-7209AFF30749@dsl-only.net> References: <bug-26519-7604@http.bugs.llvm.org/> <bug-26519-7604-UhFFHDCAay@http.bugs.llvm.org/> <0103401A-CEEA-4992-A45E-E60EA151119B@dsl-only.net> <893ECA11-7C80-4D24-A496-92ADC7978A07@FreeBSD.org> <8F708AD1-055E-41BD-BD92-6A87C5FBAA60@dsl-only.net> <78CD5050-2B2B-4213-AF11-7EF744F608B2@dsl-only.net> <E177E5EE-25EB-4CBA-9C0F-7209AFF30749@dsl-only.net>
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On 2017-May-5, at 6:11 PM, Mark Millard <markmi@dsl-only.net> wrote: > On 2017-May-5, at 1:22 AM, Mark Millard <markmi@dsl-only.net> wrote: >=20 >> On 2017-May-5, at 12:45 AM, Mark Millard <markmi at dsl-only.net> = wrote: >>=20 >>> On 2017-May-4, at 2:41 PM, Dimitry Andric <dim at FreeBSD.org> = wrote: >>>=20 >>>> . . . >>>> Thanks for the notice. I have merged the upstream fix into head in >>>> r317810, and I will MFC it after a few days. >>>=20 >>> I now have an old PowerMac running: >>>=20 >>> # uname -paKU >>> FreeBSD FBSDG4S 12.0-CURRENT FreeBSD 12.0-CURRENT r317820M powerpc = powerpc 1200030 1200030 >>>=20 >>> where buildworld was via clang 4 (an amd64->powerpc >>> cross build). Even the classic tiny program that >>> previously showed C++ exception handling was broken >>> and would crash the program now works when >>> re-compiled and re-linked. Commands that were >>> previous broken now work. >=20 > I messed up and accidentally installed the > gcc 4.2.1 world that I had also built. This > is why C++ exceptions appeared to be working > for powerpc. >=20 > Both TARGET_ARCH=3Dpowerpc and TARGET_ARCH=3Dpowerpc64 > have C++ exceptions still messed up. >=20 >=20 >>> . . . >>>=20 >>> For the gcc 4.2.1 based kernel boot I have >>> had one odd fatal kernel trap (0x903a64a, >>> "unknown") where the lr showed 0x907f . It >>> reported being stopped at: >>>=20 >>> ffs_truncate+0x1080 >>>=20 >>> It appears that "call doadump" worked but >>> I've not looked at what was put in >>> /var/crash/ . >>=20 >> If I leave the PowerMac idle running: >>=20 >> # uname -paKU >> FreeBSD FBSDG4S 12.0-CURRENT FreeBSD 12.0-CURRENT r317820M powerpc = powerpc 1200030 1200030 >>=20 >> it eventually gets the same ffs_truncate-tied fatal >> kernel trap, with the same odd lr and the like. >>=20 >> So, while I cannot directly cause the problem >> at a specific time, the problem is repeatable. >>=20 >> I did not build the kernel with a so-called >> "red-zone" to work around any stack-operation >> ordering problems that might still be around. >> But I do not know that such is involved here. >> It may be a while before I manage to get that >> much of an analysis done. >=20 > The ffs_truncate issue is odd: >=20 > A) It was gcc 4.2.1 based for both kernel and world. > B) I built a gcc 4.2.1 based debug kernel and > installed it but that does not get the problem. >=20 > I sam trying the gcc 4.2.1 debug kernel with the > system clang 4 world now and will later switch > to the gcc 4.2.1 non-debug kernel to see what > happens. >=20 > But being a pure gcc 4.2.1 environment originally > suggests that the ffs_truncate issue is not > clang-toolchain related. I found a bad (old) kernel module in /boot/kernel/ and eliminating it appears to have removed the ffs_truncate problem. And even more good news: buildworld buildkernel makes extensive use of signals and its failure is how I discovered the original stack handling problems for powerpc (the ABI violations). I used to have to patch in so-called "red zone" handling to avoid the issue. No more: a running a kernel that was built without a "red zone" and running a world based on clang now allows buildworld buildkernel to complete just fine: no evidence of ABI violations in the world code that is executed. Going the other direction: I've conformed that clang still generates C++ programs that can not handle thrown exceptions. Both powerpc and powerpc64 are this way. The only other area with an issue that I know of is the exec /sbin/init failure that prevents using the clang based kernel for powerpc. (This is based on the system binutils for powerpc and devel/*binutils for powerpc64 instead of lld and such. lld has its own problems for these targets.) I already build and run powerpc64 kernels built by clang. That has been true for a while. =3D=3D=3D Mark Millard markmi at dsl-only.net
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