Date: Sun, 19 Jan 2020 18:51:17 +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 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) > > Note that there are lots of other syscalls that are unsafe to use > directly due to struct timespec/timeval mismatch between user and > kernel, but (1) clock_gettime is the only one that's widely used > because of the glibc -lrt mess, and (2) most of the others have valid > usage cases, e.g. if the times argument is just a timeout and you're > calling them without a timeout (null pointer). So I think it suffices > to do this just for clock_gettime. > > Also note a possible variant: we could leave the definition but rename > it to SYS_clock_gettime32 so that code that's implementing its own > fallbacks with direct syscalls for whatever reasons still has access > to the syscall number if needed, but only if it's aware of the name > change. i'd ask the glibc folks if they want to do something about this when building for the time64 abi.
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