Date: Sat, 27 Oct 2018 16:33:03 -0700 From: Mark Millard <marklmi@yahoo.com> To: =?utf-8?Q?Mika=C3=ABl_Urankar?= <mikael.urankar@gmail.com>, Sean Bruno <sbruno@freebsd.org> Cc: FreeBSD Toolchain <freebsd-toolchain@freebsd.org>, freeBSD <freebsd-hackers@freebsd.org>, FreeBSD Ports ML <freebsd-ports@freebsd.org> Subject: Re: head -r339076 amd64 -> armv7 port cross build attempt with native tools involved: hangs between a cc (wait) and its child ld (uwait) Message-ID: <E0E27A7F-D4F5-450B-B6FE-03664E48D3BB@yahoo.com> In-Reply-To: <CBB0AC55-9EFE-4B58-8139-CE7CC265BF21@yahoo.com> References: <33C58480-1E76-4748-83B4-CB39FAD8584A@yahoo.com> <CAJwjRmS0u6ONZTOX%2B-aFuOjm2FFDR-vkSO8h4j47d5OODPsDjA@mail.gmail.com> <D3CCBEF4-BCEF-4D6F-A503-AAE512D3D875@yahoo.com> <CBB0AC55-9EFE-4B58-8139-CE7CC265BF21@yahoo.com>
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[Some of this discussion occurred off list. The point here is not specific to the hang that I originally reported.] On 2018-Oct-27, at 3:03 PM, Mark Millard <marklmi at yahoo.com> wrote: >=20 >> . . . >>=20 >>=20 >>> There are bugs in qemu that can cause such deadlock, you can try = these >>> 2 patches: >>> = https://github.com/MikaelUrankar/qemu-bsd-user/commit/9424a5ffde4de2768ab6= baa45fdbe0dbb56a7371 >>> = https://github.com/MikaelUrankar/qemu-bsd-user/commit/d6f65a7f07d280b6906d= 499d8e465d4d2026c52b >>=20 >> I'll try those later. Thanks. (I need to get back to sleep.) >>=20 >> It was interesting that attach/detach to the ld process >> caused it to progress. The rest of the build completed >> just fine. But that one spot consistently hung up before >> trying gdb to look at the back trace. >>=20 >=20 > Looking at the qemu code related to the 2nd patch: the > structure of the field copies (via __get_user) seems > very sensitive to the ABI rules for the target and > how things align and such, given that the structure > description and code are host code. __packed vs. not > is possibly not sufficient control to always make things > match right across all the potential combinations of > host and target from what I can see. >=20 > Lack of __packed may prove sufficient for my specific > context (amd64 host and armv7 target) but it seems > non-obvious what to do in general. >=20 > There would also seem to be big endian vs. little endian > issues on the individual __get_user styles of copies > when the host and target do not match for a multi-byte > numeric encoding. Well, I get the following for: #include "/usr/include/sys/event.h" // kevent #include <stddef.h> // offsetof #include <stdio.h> // printf int main() { printf("%lu\n", (unsigned long) sizeof(struct kevent)); printf("ident %lu\n", (unsigned long) offsetof(struct kevent, = ident)); printf("filter %lu\n", (unsigned long) offsetof(struct kevent, = filter)); printf("flags %lu\n", (unsigned long) offsetof(struct kevent, = flags)); printf("fflags %lu\n", (unsigned long) offsetof(struct kevent, = fflags)); printf("data %lu\n", (unsigned long) offsetof(struct kevent, = data)); printf("udata %lu\n", (unsigned long) offsetof(struct kevent, = udata)); printf("ext %lu\n", (unsigned long) offsetof(struct kevent, = ext)); return 0; } (This code avoided warnings for type mismatches with the printf strings and such.) amd64 native [host of qemu use] (comments hand added): # ./a.out 64 ident 0 filter 8 // NOTE! flags 10 // NOTE! fflags 12 // NOTE! data 16 udata 24 ext 32 (The above is not particularly important but I include it for completeness.) armv7 native [target in qemu use] (comments hand added): # ./a.out 64 // NOTE vs. below! ident 0 filter 4 // NOTE vs. above! flags 6 // NOTE vs. above! fflags 8 // NOTE vs. above! data 16 // NOTE vs. below! udata 24 // NOTE vs. below! ext 32 // NOTE vs. below! /usr/include/sys/event.h lacks __packed in both cases. With __packed in qemu-arm-static's source code for target_freebsd_kevent I confirm that via gdb for the qemu-arm-static: p/d sizeof(struct target_freebsd_kevent) p/d &((struct target_freebsd_kevent *)0)->ident p/d &((struct target_freebsd_kevent *)0)->filter p/d &((struct target_freebsd_kevent *)0)->flags p/d &((struct target_freebsd_kevent *)0)->fflags p/d &((struct target_freebsd_kevent *)0)->data p/d &((struct target_freebsd_kevent *)0)->udata p/d &((struct target_freebsd_kevent *)0)->ext reports as the 2nd patch's problem-report material reports (56,0,4,6,8,12,20,24): not even the right size. I also confirm that removing __packed in qemu's code and rebuilding and then checking with gdb reported a match to the above armv7 native report (64,0,4,6,8,16,24,32). I have not verified __packed used vs. not for any other combination of host and target platforms. =3D=3D=3D Mark Millard marklmi at yahoo.com ( dsl-only.net went away in early 2018-Mar)
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