Date: Sun, 19 Jan 2020 19:42:26 +0100 From: Szabolcs Nagy <nsz@...t70.net> To: musl@...ts.openwall.com Subject: Re: [RFC] removing __NR_clock_gettime / SYS_clock_gettime * Rich Felker <dalias@...c.org> [2020-01-19 13:16:43 -0500]: > On Sun, Jan 19, 2020 at 06:51:17PM +0100, Szabolcs Nagy wrote: > > * Rich Felker <dalias@...c.org> [2020-01-19 11:36:16 -0500]: > > > Today we discovered that libstdc++ std::chrono is broken because it's > > > making direct syscalls to SYS_clock_gettime to work around glibc > > > putting clock_gettime in librt. This is exactly the same issue as > > > busybox https://bugs.busybox.net/show_bug.cgi?id=12091 and I would not > > > be surprised if it exists in more software. It's a silent bug that's > > > easy to find and fix if you know what to look for, but very confusing > > > and hard to find if you don't, and it can easily slip into software > > > that's not well-tested on time64. > > > > > > What I'd like to propose doing is removing __NR_clock_gettime and > > > SYS_clock_gettime from the public sys/syscall.h (via bits headers) on > > > 32-bit archs, and moving SYS_clock_gettime to > > > arch/$(ARCH)/syscall_arch.h for musl-internal use. This would make it > > > a hard compile-time error for any software attempting to use the > > > syscall directly, and in the case of libstdc++ I think it would even > > > fix the problem without patching gcc, since they have a configure > > > check for the syscall. > > > > > > Thoughts? Is this too big a hammer? > > > > i think you should build gcc with --enable-libstdcxx-time so > > it does not try to do raw syscalls (which is bad on 64bit > > targets too, not just for time64, i thought distros already > > do this or patch out that entire thing) > > It does raw syscalls with that as I understand it. You need =rt to > make it do the right thing. --enable-libstdcxx-time is default in mcm since commit 0291cc44eee410270a97efb6258394c1f1f8352a Commit: Rich Felker <dalias@...ifal.cx> CommitDate: 2016-05-06 18:37:09 +0000 and the libstdc++ i built with that only has SYS_futex syscalls in it on all targets. now i see that alpine libstdc++ has a raw clock_gettime syscall in it too, alpine should fix that. > > But we know how to fix this for gcc now. I'm more concerned that if we > already caught busybox and libstdc++ doing this, there may be lots > more apps doing it that we don't know about... i see, i'm not sure what's the right solution. we can try to fix them or break their build. some usage may be valid though. > > i'd ask the glibc folks if they want to do something about this > > when building for the time64 abi. > > I think they just use the kernel headers to provide sys/syscall.h. well if there are really raw syscall users with libc type then glibc will have a problem too, so either the user code gets fixed or glibc does some workaround.
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