Date: Fri, 4 Jan 2019 01:17:52 -0800 From: Mark Millard <marklmi@yahoo.com> To: mmel@freebsd.org Cc: Dennis Clarke <dclarke@blastwave.org>, freebsd-arm@freebsd.org, FreeBSD Current <freebsd-current@freebsd.org> Subject: Re: A reliable port cross-build failure (hangup) in my context (amd64->armv7 cross build, with native-tool speedup involved) Message-ID: <F6A047AF-D7E2-4298-86A2-02DE2ABA0D17@yahoo.com> In-Reply-To: <ddae0990-f68b-549e-18da-1388e772a3ff@freebsd.org> References: <FF9B4284-4E6B-4D36-86A0-18861B527AC0@yahoo.com> <865A13C8-9749-486E-9F79-5EEDDECBE621@yahoo.com> <0154C3AC-D85B-4FCF-BA63-454BC26BC1A2@yahoo.com> <A6A58CE3-062B-4B79-A8C2-ADFDAA04C6AF@yahoo.com> <13f5e4dd-33fb-2170-e31a-1b5d5f155869@freebsd.org> <ABA957EA-B8EE-4B8C-9C2F-B745BA652BF6@yahoo.com> <2E3F6196-4652-40D2-937F-8860B6005A35@yahoo.com> <d99f28fd-5c6c-db6f-2d78-9ea6a697af2e@blastwave.org> <ddae0990-f68b-549e-18da-1388e772a3ff@freebsd.org>
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On 2019-Jan-3, at 22:56, Michal Meloun <melounmichal at gmail.com> wrote: > On 29.12.2018 18:47, Dennis Clarke wrote: >> On 12/28/18 9:56 PM, Mark Millard via freebsd-arm wrote: >>> >>> On 2018-Dec-28, at 12:12, Mark Millard <marklmi at yahoo.com> wrote: >>> >>>> On 2018-Dec-28, at 05:13, Michal Meloun <melounmichal at gmail.com> >>>> wrote: >>>> >>>>> Mark, >>>>> this is known problem with qemu-user-static. >>>>> Emulation of every single interruptible syscall is broken by design (it >>>>> have signal related races). Theses races cannot be solved without major >>>>> rewrite of syscall emulation code. >>>>> Unfortunately, nobody actively works on this, I think. >>>>> >> >> Following along here quietly and I had to blink at this a few times. >> Is there a bug report somewhere within the qemu world related to this >> 'broken by design' qemu feature? > > Firstly, I apologize for late answer. Writing a technically accurate but > still comprehensible report is extremely difficult for me. Thanks for doing so. > . . . > Mark, I hope that this is also the answer to your question posted to > hackers@ and also the exploitation why you see hang. Again thanks: it was helpful for my gaining some understanding of the code structure. But it turns out that another of your list of problems is involved in the hang-up: > . . . > - and last major one. At this time, all guest structures are maintained > by hand. Due to huge amount of these structures, this is the extreme > error prone approach. We should convert this to script generated code, > including guest syscalls definition. It turns out that "struct target_cmsghdr" has the wrong overall size, the wrong first field size, and the wrong offsets for later fields for amd64->aarch64 use (or likely any 64-bit->64-bit host-target pair, even amd64->x86_64). In fact the code reports via: gemu_log("Unsupported ancillary data: %d/%d\n", cmsg->cmsg_level, cmsg->cmsg_type); because of msg->cmsg_level and cmsg->cmsg_type ending up with messed up values. It hangs after that message shows up. The more complete code containing that qemu_log call is: if ((cmsg->cmsg_level == TARGET_SOL_SOCKET) && (cmsg->cmsg_type == SCM_RIGHTS)) { int *fd = (int *)data; int *target_fd = (int *)target_data; int i, numfds = len / sizeof(int); for (i = 0; i < numfds; i++) { fd[i] = tswap32(target_fd[i]); } } else if ((cmsg->cmsg_level == TARGET_SOL_SOCKET) && (cmsg->cmsg_type == SCM_TIMESTAMP) && (len == sizeof(struct timeval))) { /* copy struct timeval to host */ struct timeval *tv = (struct timeval *)data; struct target_freebsd_timeval *target_tv = (struct target_freebsd_timeval *)target_data; __get_user(tv->tv_sec, &target_tv->tv_sec); __get_user(tv->tv_usec, &target_tv->tv_usec); } else { gemu_log("Unsupported ancillary data: %d/%d\n", cmsg->cmsg_level, cmsg->cmsg_type); memcpy(data, target_data, len); } Of 3 types of hangups that I've run into recently, one was from a missing statement, one was from struct target_kevent having the wrong overall size and wrong field offsets after the first field (amd64->armv7 was an example), and the one involving struct target_cmsghdr above. (There may be more to the target_cmsghdr one.) > Again, my apology for slightly (or much) chaotic report, but this is the > best what's I capable. Not chaotic in my view. === Mark Millard marklmi at yahoo.com ( dsl-only.net went away in early 2018-Mar)
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