Date: Sun, 21 Feb 2016 03:52:41 -0800 From: Mark Millard <markmi@dsl-only.net> To: Roman Divacky <rdivacky@freebsd.org> Cc: Dimitry Andric <dim@FreeBSD.org>, FreeBSD Toolchain <freebsd-toolchain@freebsd.org>, FreeBSD PowerPC ML <freebsd-ppc@freebsd.org> Subject: Re: I've submitted 207175 for a clang 3.8.0 va_list handling problem for powerpc [fpr use also tested] Message-ID: <1047AD1A-BCE1-44B0-A649-60343A89207D@dsl-only.net> In-Reply-To: <20160221090215.GA21511@vlakno.cz> References: <3A260EC5-E69A-4980-8F74-C04395F4E5F4@dsl-only.net> <20160215201800.GA20796@vlakno.cz> <D702187C-6B8C-42AC-855D-45A570FDB0FA@dsl-only.net> <D3351840-02B5-4696-8163-D90A6E039E4C@dsl-only.net> <74577A87-3006-43A9-9EAB-F51D946B6245@dsl-only.net> <28FF474D-2109-4605-8B2B-C5374CBCCF42@dsl-only.net> <8EB46124-3335-4643-8C64-16DA56D481F5@dsl-only.net> <8C40A5D7-C0B8-4142-89D4-228017C446CE@dsl-only.net> <20160220083450.GA55777@vlakno.cz> <68D66F67-EC4D-4CF2-A249-C7F0C4D4747D@FreeBSD.org> <20160221090215.GA21511@vlakno.cz>
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On 2016-Feb-21, at 1:02 AM, Roman Divacky <rdivacky at freebsd.org> = wrote: >=20 > On Sat, Feb 20, 2016 at 03:26:58PM +0100, Dimitry Andric wrote: >> On 20 Feb 2016, at 09:34, Roman Divacky <rdivacky at vlakno.cz> = wrote: >>> Fwiw, I've just committed the patch to clang in r261422. You might = want >>> to keep using a local modification or ask dim@ to import that patch >>> to our copy of 3.8. >>=20 >> I've asked the LLVM release manager to consider merging this into the >> 3.8 branch. The fix looks trivial enough. :) >>=20 >> -Dimitry >>=20 >=20 > Cool :) >=20 > Mark, so what remains broken now beside the C++ exceptions? Also, can = you try > to take a look at kernel? >=20 > Thanks! Roman Implication of the below detailed answer: I've not thought about the = kernel much so far and it may well be some time before I do. Getting each thing fixed/operable/improved/worked-around for = world/userland has helped me explore finding the next thing. The C++ = exception problems currently block using "kyua -k /usr/tests/Kyuafile", = something I've been hoping to be able to do as evidence for how much is = (then) working based on a clang 3.8.0 buildworld. I've been sticking to = providing evidence for details world/userland issues before tackling = anything else. (So far I'm not generally fixing things, mostly just = finding evidence of problem details.) You may not know that I run PowerPC (32-bit) with modified signal = delivery: my adjustment uses a so-called "red-zone" to avoid the = incorrect timing of the stack pointer adjustments that clang 3.8.0's = code generation produces. (An ABI violation that I've worked around for = world/userland.) The work around was required to be able to have a = self-hosted buildworld's complete without make getting SEGV's/BusError's = that stop the build. No one is working on clang 3.8.0's 32-bit PowerPC stack-pointer-handling = ABI violations so far as I know. I doubt anyone will tackle the kernel overall for 32-bit PowerPC as long = as the stack pointer is decremented late and incremented early in = clang's generated code. I expect that handling such is comparatively = simple in world/userland (see above) compared to in the kernel and the = kernel's handling of is own stack. I doubt that FreeBSD would make even the red-zone code change for = world/userland official. It is operationally compatible with the = official ABI in world/userland but is temporarily somewhat wasteful of = some stack bytes. But mostly it is just something not required by the = official ABI and the signal delivery change does not help the = bigger/messier kernel-stack handling issue. I doubt FreeBSD would ever officially split buildworld and buildkernel = by using different compilers as I have, even temporarily. So no official = PowerPC clang context until everything works for both parts would be my = guess. I just view the split as a development/testing technique for = helping find details of problems in the simpler world/userland context = first. I did once take a quick look at clang 3.8.0 use in buildkernel instead = of using gcc 4.2.1. I do not remember all the details but one thing that = I remember is that clang's integrated-assembler notation and the = kernel's source files did not agree in various places. I have no formal descriptions of the two assembler notations or = description of how they correspond where different. This tends to = prevent any systematic process for such issues. (I'm no PowerPC = assembler expert: I look things up as I go.) If I remember the count right I also identified two other kernel = points-for-investigation very quickly and stopped there in order to = continue with world/userland investigations. I was guessing there was a = lot more to find relative to the kernel based on how quickly those 3 = subject areas were found. Since I started exploring FreeBSD I've observed that things happen = without prior notice that suspend my FreeBSD activity for weeks or = months at a time. That has happened several times. So I'm not sure how = far I'll get before such happens again. And PowerPC access has that issue even more: I can end up without access = to the old PowerMacs for long periods even if I can spend some time = exploring some (other) aspects of FreeBSD at the time. At this point I've no clue how I'll find what specific details are = involved in the "clang 3.8.0 compiled C++ exception infrastructure vs. = clang++380/g++5/g++49/g++421 compiled code" mismatch. I've no clue how = long that will take. So, overall, I'm not ready to think much about the kernel yet. =3D=3D=3D Mark Millard markmi at dsl-only.net
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