Okay, i'm in the http://distfiles.gentoo.org/experimental/arm/musl/stage3-armv7a_hardfp-musl-vanilla-20160606.tar.bz2 chroot, using qemu-2.6.0 on a hardened amd64 glibc gentoo linux host. # /usr/bin/install-xattr Segmentation fault BUT # qemu-arm /usr/bin/install-xattr /usr/bin/install: missing file operand Try '/usr/bin/install --help' for more information.
Your description of the problem is not sufficent. Please provide more detail on how to reproduce the problem.
emerge qemu w/ arm target and static-user # /etc/init.d/qemu-binfmt start Get the stage3. Unpack it. # cp /usr/bin/qemu-arm stage3/usr/bin/qemu-arm # chroot stage3 /bin/bash # install-xattr
Do most other binaries work? If so, this would be more likely a bug in intall-xattr than in qemu.
(In reply to Mike Gilbert from comment #3) > Do most other binaries work? If so, this would be more likely a bug in > intall-xattr than in qemu. Yes, at least it succeeds in compiling a basic system for me.
(In reply to Sergey 'L29Ah' Alirzaev from comment #4) > (In reply to Mike Gilbert from comment #3) > > Do most other binaries work? If so, this would be more likely a bug in > > intall-xattr than in qemu. > > Yes, at least it succeeds in compiling a basic system for me. I don't get this because the stage3 wouldn't even build if install-xattr seg faulted. I build on native hardware. Can you get me a strace and a backtrace with gdb?
Somehow it started to "work". I guess that's because i've built qemu with USE=debug or updated my kernel: l29ah-x201 / # install-xattr install-xattr: failed to find 'install' in PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/opt/bin:/usr/armv7a-hardfloat-linux-musleabi/gcc-bin/4.9.3: No such file or directory l29ah-x201 / # which install /usr/bin/install l29ah-x201 / # install /usr/bin/install: missing file operand Try '/usr/bin/install --help' for more information. l29ah-x201 / # /usr/bin/install /usr/bin/install: missing file operand Try '/usr/bin/install --help' for more information. l29ah-x201 / # strace install-xattr qemu: Unsupported syscall: 26 qemu: Unsupported syscall: 26 /usr/bin/strace: ptrace(PTRACE_TRACEME, ...): Function not implemented +++ exited with 1 +++ Removed the flag, but it refuses to build now (maybe because of upgrading to dev-libs/glib-2.48.1): >>> Starting src_configure ../configure --prefix=/usr --sysconfdir=/etc --libdir=/usr/lib64 --docdir=/usr/share/doc/qemu-2.6.0/html --disable-bsd-user --disable-guest-agent --disable-strip --disable-werror --disable-gcrypt --python=/usr/bin/python2.7 --cc=x86_64-pc-linux-gnu-gcc --cxx=x86_64-pc-linux-gnu-g++ --host-cc=x86_64-pc-linux-gnu-gcc --disable-debug-info --disable-debug-tcg --enable-docs --disable-tcg-interpreter --enable-attr --disable-brlapi --enable-linux-aio --disable-bluez --enable-cap-ng --enable-curl --enable-fdt --disable-glusterfs --disable-gnutls --disable-nettle --disable-gtk --disable-rdma --disable-libiscsi --enable-vnc-jpeg --enable-kvm --disable-lzo --enable-curses --disable-libnfs --disable-numa --enable-opengl --enable-vnc-png --disable-rbd --disable-vnc-sasl --disable-sdl --disable-seccomp --disable-smartcard --disable-snappy --enable-spice --disable-libssh2 --enable-libusb --disable-usb-redir --enable-uuid --disable-vde --enable-vhost-net --disable-virglrenderer --enable-virtfs --enable-vnc --disable-vte --disable-xen --disable-xen-pci-passthrough --disable-xfsctl --disable-linux-user --enable-system --with-system-pixman --audio-drv-list=alsa,oss --target-list=i386-softmmu,x86_64-softmmu --enable-pie Install prefix /usr BIOS directory /usr/share/qemu binary directory /usr/bin library directory /usr/lib64 module directory /usr/lib64/qemu libexec directory /usr/libexec include directory /usr/include config directory /etc local state directory /usr/var Manual directory /usr/share/man ELF interp prefix /usr/gnemul/qemu-%M Source path /var/tmp/paludis/app-emulation-qemu-2.6.0/work/qemu-2.6.0 C compiler x86_64-pc-linux-gnu-gcc Host C compiler x86_64-pc-linux-gnu-gcc C++ compiler x86_64-pc-linux-gnu-g++ Objective-C compiler clang ARFLAGS rv CFLAGS -pthread -I/usr/include/glib-2.0 -I/usr/lib64/glib-2.0/include -O2 -pipe -O2 -pipe -march=native QEMU_CFLAGS -I/usr/include/pixman-1 -fPIE -DPIE -m64 -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -Wstrict-prototypes -Wredundant-decls -Wall -Wundef -Wwrite-strings -Wmissing-prototypes -fno-strict-aliasing -fno-common -Wendif-labels -Wmissing-include-dirs -Wempty-body -Wnested-externs -Wformat-security -Wformat-y2k -Winit-self -Wignored-qualifiers -Wold-style-declaration -Wold-style-definition -Wtype-limits -fstack-protector-strong -I/usr/include/libpng16 -I/usr/include/spice-server -I/usr/include/glib-2.0 -I/usr/lib64/glib-2.0/include -I/usr/include/pixman-1 -I/usr/include/spice-1 -I/usr/include/libusb-1.0 LDFLAGS -Wl,--warn-common -Wl,-z,relro -Wl,-z,now -pie -m64 -Wl,-O1 -Wl,--as-needed make make install install python /usr/bin/python2.7 -B smbd /usr/sbin/smbd module support no host CPU x86_64 host big endian no target list i386-softmmu x86_64-softmmu tcg debug enabled no gprof enabled no sparse enabled no strip binaries no profiler no static build no pixman system SDL support no GTK support no GTK GL support no GNUTLS support no GNUTLS hash no GNUTLS rnd no libgcrypt no libgcrypt kdf no nettle no nettle kdf no libtasn1 yes VTE support no curses support yes virgl support no curl support yes mingw32 support no Audio drivers alsa oss Block whitelist (rw) Block whitelist (ro) VirtFS support yes VNC support yes VNC SASL support no VNC JPEG support yes VNC PNG support yes xen support no brlapi support no bluez support no Documentation yes PIE yes vde support no netmap support no Linux AIO support yes ATTR/XATTR support yes Install blobs yes KVM support yes RDMA support no TCG interpreter no fdt support yes preadv support yes fdatasync yes madvise yes posix_madvise yes sigev_thread_id yes uuid support yes libcap-ng support yes vhost-net support yes vhost-scsi support yes Trace backends log spice support yes (0.12.11/0.13.1) rbd support no xfsctl support no smartcard support no libusb yes usb net redir no OpenGL support yes OpenGL dmabufs yes libiscsi support no libnfs support no build guest agent no QGA VSS support no QGA w32 disk info no QGA MSI support no seccomp support no coroutine backend ucontext coroutine pool yes GlusterFS support no Archipelago support no gcov gcov gcov enabled no TPM support yes libssh2 support no TPM passthrough yes QOM debugging yes vhdx yes lzo support no snappy support no bzip2 support yes NUMA host support no tcmalloc support no jemalloc support no avx2 optimization yes ../configure --prefix=/usr --sysconfdir=/etc --libdir=/usr/lib64 --docdir=/usr/share/doc/qemu-2.6.0/html --disable-bsd-user --disable-guest-agent --disable-strip --disable-werror --disable-gcrypt --python=/usr/bin/python2.7 --cc=x86_64-pc-linux-gnu-gcc --cxx=x86_64-pc-linux-gnu-g++ --host-cc=x86_64-pc-linux-gnu-gcc --disable-debug-info --disable-debug-tcg --enable-docs --disable-tcg-interpreter --enable-attr --disable-brlapi --disable-linux-aio --disable-bluez --disable-cap-ng --disable-curl --disable-fdt --disable-glusterfs --disable-gnutls --disable-nettle --disable-gtk --disable-rdma --disable-libiscsi --disable-vnc-jpeg --disable-kvm --disable-lzo --disable-curses --disable-libnfs --disable-numa --disable-opengl --disable-vnc-png --disable-rbd --disable-vnc-sasl --disable-sdl --disable-seccomp --disable-smartcard --disable-snappy --disable-spice --disable-libssh2 --disable-libusb --disable-usb-redir --disable-uuid --disable-vde --disable-vhost-net --disable-virglrenderer --disable-virtfs --disable-vnc --disable-vte --disable-xen --disable-xen-pci-passthrough --disable-xfsctl --enable-linux-user --disable-system --disable-blobs --disable-tools --target-list=arm-linux-user,i386-linux-user,x86_64-linux-user --static --disable-pie Error: * In program /usr/bin/cave --colour yes perform install --hooks --managed-output --output-exclusivity with-others =app-emulation/qemu-2.6.0:0::gentoo --destination installed --replacing =app-emulation/qemu-2.6.0:0::installed --x-of-y 1 of 1: * When installing 'app-emulation/qemu-2.6.0:0::gentoo' replacing { 'app-emulation/qemu-2.6.0:0::installed' }: * When running an ebuild command on 'app-emulation/qemu-2.6.0:0::gentoo': * Install failed for 'app-emulation/qemu-2.6.0:0::gentoo' (paludis::ActionFailedError) ERROR: sizeof(size_t) doesn't match GLIB_SIZEOF_SIZE_T. You probably need to set PKG_CONFIG_LIBDIR to point to the right pkg-config files for your build target
(In reply to Sergey 'L29Ah' Alirzaev from comment #6) > l29ah-x201 / # strace install-xattr > qemu: Unsupported syscall: 26 > qemu: Unsupported syscall: 26 > /usr/bin/strace: ptrace(PTRACE_TRACEME, ...): Function not implemented > +++ exited with 1 +++ I've seen this happen before with qemu + arm, but I forget the details. There's nothing to fix in musl or install-xattr. Unless you can narrow it more and want to pursue this with qemu, we should close this bug.
(In reply to Sergey 'L29Ah' Alirzaev from comment #6) > Somehow it started to "work". I guess that's because i've built qemu with > USE=debug or updated my kernel: Sorry I quoted the wrong section in my previous comment making it sound like I was referring to the failed strace. That's because of a missing sys_ptrace, which is unrelated to the original seg fault.
(In reply to Anthony Basile from comment #8) correct, strace is not usable under qemu you can try exporting QEMU_STRACE=1 though and qemu itself will do the syscall tracing for you
(In reply to Sergey 'L29Ah' Alirzaev from comment #6) > Somehow it started to "work". I guess that's because i've built qemu with > USE=debug or updated my kernel: I just tested on native hardware, exact same stage as above, and it worked. I think this is a problem with qemu+arm.
So what's invalid about the report?
(In reply to Sergey 'L29Ah' Alirzaev from comment #11) > So what's invalid about the report? (In reply to Sergey 'L29Ah' Alirzaev from comment #6) > Somehow it started to "work". This is in contradiction to the title. INVALID doesn't mean you didn't hit some problem, just that there's nothing here to act on. We don't have any better category to use. Its not NEEDINFO because install-xattr works, nor is it an identified bug in qemu. So ...?
(In reply to Anthony Basile from comment #12) > (In reply to Sergey 'L29Ah' Alirzaev from comment #11) > > So what's invalid about the report? > > (In reply to Sergey 'L29Ah' Alirzaev from comment #6) > > Somehow it started to "work". > > This is in contradiction to the title. "Work" ≠ work. > INVALID doesn't mean you didn't hit some problem, just that there's nothing > here to act on. We don't have any better category to use. Its not NEEDINFO > because install-xattr works, nor is it an identified bug in qemu. So ...? # QEMU_STRACE=1 install-xattr 18111 set_tid_address(-159391584,0,1,-159391204,-159391612,-150999136) = 18111 18111 mprotect(0xf67fb000,4096,PROT_READ) = 0 18111 mprotect(0x00021000,4096,PROT_READ) = 0 18111 open("/proc/self/exe",O_RDONLY|O_LARGEFILE|O_NONBLOCK|O_CLOEXEC|O_PATH) = 3 18111 readlink("/proc/self/fd/3",0xf6ffde88,4095) = -1 errno=2 (No such file or directory) 18111 close(3) = -1 errno=9 (Bad file descriptor) 18111 rt_sigprocmask(SIG_BLOCK,0xf67ead50,0xf6ffee10) = 0 18111 fork() = 18114 = 0 18111 rt_sigprocmask(SIG_SETMASK,0xf6ffee10,NULL) = 0 18114 gettid(0,-159470256,-150999536,-159391408,0,-150999536) = 18114 18114 rt_sigprocmask(SIG_SETMASK,0xf6ffee10,NULL) = 0 18111 wait4(-1,-150999372,0,0,0,0)18114 open("/root/bin//install",O_RDONLY|O_LARGEFILE|O_NONBLOCK|O_CLOEXEC|O_PATH) = -1 errno=2 (No such file or directory) 18114 open("/usr/local/sbin/install",O_RDONLY|O_LARGEFILE|O_NONBLOCK|O_CLOEXEC|O_PATH) = -1 errno=2 (No such file or directory) 18114 open("/usr/local/bin/install",O_RDONLY|O_LARGEFILE|O_NONBLOCK|O_CLOEXEC|O_PATH) = -1 errno=2 (No such file or directory) 18114 open("/usr/sbin/install",O_RDONLY|O_LARGEFILE|O_NONBLOCK|O_CLOEXEC|O_PATH) = -1 errno=2 (No such file or directory) 18114 open("/usr/bin/install",O_RDONLY|O_LARGEFILE|O_NONBLOCK|O_CLOEXEC|O_PATH) = 3 18114 readlink("/proc/self/fd/3",0xf6ffdde8,4095) = -1 errno=2 (No such file or directory) 18114 close(3) = 0 18114 open("/sbin/install",O_RDONLY|O_LARGEFILE|O_NONBLOCK|O_CLOEXEC|O_PATH) = -1 errno=2 (No such file or directory) 18114 open("/bin/install",O_RDONLY|O_LARGEFILE|O_NONBLOCK|O_CLOEXEC|O_PATH) = -1 errno=2 (No such file or directory) 18114 open("/usr/local/sbin/install",O_RDONLY|O_LARGEFILE|O_NONBLOCK|O_CLOEXEC|O_PATH) = -1 errno=2 (No such file or directory) 18114 open("/usr/local/bin/install",O_RDONLY|O_LARGEFILE|O_NONBLOCK|O_CLOEXEC|O_PATH) = -1 errno=2 (No such file or directory) 18114 open("/usr/sbin/install",O_RDONLY|O_LARGEFILE|O_NONBLOCK|O_CLOEXEC|O_PATH) = -1 errno=2 (No such file or directory) 18114 open("/usr/bin/install",O_RDONLY|O_LARGEFILE|O_NONBLOCK|O_CLOEXEC|O_PATH) = 3 18114 readlink("/proc/self/fd/3",0xf6ffdde8,4095) = -1 errno=2 (No such file or directory) 18114 close(3) = 0 18114 open("/sbin/install",O_RDONLY|O_LARGEFILE|O_NONBLOCK|O_CLOEXEC|O_PATH) = -1 errno=2 (No such file or directory) 18114 open("/bin/install",O_RDONLY|O_LARGEFILE|O_NONBLOCK|O_CLOEXEC|O_PATH) = -1 errno=2 (No such file or directory) 18114 open("/opt/bin/install",O_RDONLY|O_LARGEFILE|O_NONBLOCK|O_CLOEXEC|O_PATH) = -1 errno=2 (No such file or directory) 18114 open("/usr/x86_64-pc-linux-gnu/gcc-bin/4.9.3/install",O_RDONLY|O_LARGEFILE|O_NONBLOCK|O_CLOEXEC|O_PATH) = -1 errno=2 (No such file or directory) 18114 open("/usr/lib/plan9/bin/install",O_RDONLY|O_LARGEFILE|O_NONBLOCK|O_CLOEXEC|O_PATH) = -1 errno=2 (No such file or directory) 18114 open("/opt/eagle-5.11.0/bin/install",O_RDONLY|O_LARGEFILE|O_NONBLOCK|O_CLOEXEC|O_PATH) = -1 errno=2 (No such file or directory) 18114 writev(2,0xf6ffec80,0x2)install-xattr: = 15 18114 writev(2,0xf6ffe9a0,0x2)failed to find 'install' in PATH=/root/bin/:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/opt/bin:/usr/x86_64-pc-linux-gnu/gcc-bin/4.9.3:/usr/lib/plan9/bin:/opt/eagle-5.11.0/bin = 254 18114 writev(2,0xf6ffec98,0x2) = 0 18114 writev(2,0xf6ffed70,0x2): = 2 18114 writev(2,0xf6ffed78,0x2)No such file or directory = 25 18114 writev(2,0xf6ffeda0,0x2) = 1 18114 exit_group(1) = 18114 18111 exit_group(1) Okay, i've mounted /proc: # QEMU_STRACE=1 install-xattr 20776 set_tid_address(-159391584,0,1,-159391204,-159391612,-150999136) = 20776 20776 mprotect(0xf67fb000,4096,PROT_READ) = 0 20776 mprotect(0x00021000,4096,PROT_READ) = 0 20776 open("/proc/self/exe",O_RDONLY|O_LARGEFILE|O_NONBLOCK|O_CLOEXEC|O_PATH) = 3 20776 readlink("/proc/self/fd/3",0xf6ffde88,4095) = -1 errno=2 (No such file or directory) 20776 close(3) = -1 errno=9 (Bad file descriptor) 20776 rt_sigprocmask(SIG_BLOCK,0xf67ead50,0xf6ffee10) = 0 20776 fork() = 20779 = 0 20779 gettid(0,-159470256,-150999536,-159391408,0,-150999536) = 20779 20779 rt_sigprocmask(SIG_SETMASK,0xf6ffee10,NULL) = 0 20776 rt_sigprocmask(SIG_SETMASK,0xf6ffee10,NULL) = 0 20779 open("/root/bin//install",O_RDONLY|O_LARGEFILE|O_NONBLOCK|O_CLOEXEC|O_PATH) = -1 errno=2 (No such file or directory) 20776 20779 open("/usr/local/sbin/install",O_RDONLY|O_LARGEFILE|O_NONBLOCK|O_CLOEXEC|O_PATH) = -1 errno=2 (No such file or directory) 20779 open("/usr/local/bin/install",O_RDONLY|O_LARGEFILE|O_NONBLOCK|O_CLOEXEC|O_PATH) = -1 errno=2 (No such file or directory) 20779 open("/usr/sbin/install",O_RDONLY|O_LARGEFILE|O_NONBLOCK|O_CLOEXEC|O_PATH) = -1 errno=2 (No such file or directory) 20779 wait4(-1,-150999372,0,0,0,0)open("/usr/bin/install",O_RDONLY|O_LARGEFILE|O_NONBLOCK|O_CLOEXEC|O_PATH) = 3 20779 readlink("/proc/self/fd/3",0xf6ffdde8,4095) = 16 20779 fstat64(3,0xf6ffdd18) = 0 20779 stat64("/usr/bin/install",0xf6ffdd80) = 0 20779 close(3) = 0 = 20779 20776 getpid() = 20776 20776 kill(20776,SIGSEGV)Segmentation fault (core dumped) Not sure what to do next.
(In reply to Sergey 'L29Ah' Alirzaev from comment #13) > (In reply to Anthony Basile from comment #12) > > (In reply to Sergey 'L29Ah' Alirzaev from comment #11) > > > So what's invalid about the report? > > > > (In reply to Sergey 'L29Ah' Alirzaev from comment #6) > > > Somehow it started to "work". > > > > This is in contradiction to the title. > > "Work" ≠ work. > I misunderstood. > > > Not sure what to do next. If I have time I'll try to reproduce in qemu. As I said, this works in native hardware. The only other thing I can think of is to use gdb and get a backtrace so I can see where it happens.
Does that core dump actually get written anywhere? Maybe it would be possible to feed that to gdb somehow and get a backtrace?
(In reply to Mike Gilbert from comment #15) > Does that core dump actually get written anywhere? Maybe it would be > possible to feed that to gdb somehow and get a backtrace? I could analyze a core dump.
(In reply to Sergey 'L29Ah' Alirzaev from comment #13) running under a system where /proc or /sys isn't mounted isn't supported. if you hit a crash, that's unfortunate, but your system is misconfigured. you can also use QEMU_GDB to tell the new instance to sleep until a gdb connection is made. then connect a cross-gdb (from outside the chroot) and try to get a backtrace that way.
Is it still an issue?
Yes, It is easy to reproduce this issue today. "/usr/aarch64-gentoo-linux-musl/usr/bin/install-xattr --version" = segfault. "qemu-aarch64 /usr/aarch64-gentoo-linux-musl/usr/bin/install-xattr --version" = works fine. This issue is related to qemu code execution. I don't know even how to start debugging it. I will try to find tail that is possible to pull, but I can't guarantee result. We may need qemu core developers here.
You can use QEMU_GDB and more low-level options like '-d in_asm' to see where crash happens.
(In reply to Andrew Aladjev from comment #19) > Yes, It is easy to reproduce this issue today. > > "/usr/aarch64-gentoo-linux-musl/usr/bin/install-xattr --version" = segfault. > "qemu-aarch64 /usr/aarch64-gentoo-linux-musl/usr/bin/install-xattr > --version" = works fine. You might want to double-check how binfmt hook actually executes qemu. Lack of library search path is suspicious. qemu probably pulls in from host too much. strace would show. Here it Just Works: """ $ LANG=C /usr/bin/qemu-aarch64 -L /usr/aarch64-gentoo-linux-musl/ /usr/aarch64-gentoo-linux-musl/usr/bin/install-xattr --version install (GNU coreutils) 8.32 Packaged by Gentoo (8.32-r1 (p0)) Copyright (C) 2020 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>. This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. Written by David MacKenzie. """ > This issue is related to qemu code execution. I don't know even how to start > debugging it. I will try to find tail that is possible to pull, but I can't > guarantee result. We may need qemu core developers here. Given that there was no backtrace or core dump provided I'm closing as WORKSFORME. Feel free to reopen if you get one.
For now I am too busy. I will work on this issue a bit later. Thank you.
Hello. I've found the reason of this bug, the following line makes segfault: if (!strcmp(mypath, canpath)) "mypath" is NULL, we can see that qemu + musl library provides the following result for realpath: realpath("/proc/self/exe", NULL) == NULL I will try to diff implementations of realpath in glibc and musl.
(In reply to Andrew Aladjev from comment #23) > Hello. I've found the reason of this bug, the following line makes segfault: > > if (!strcmp(mypath, canpath)) > > "mypath" is NULL, we can see that qemu + musl library provides the following > result for realpath: > > realpath("/proc/self/exe", NULL) == NULL > > I will try to diff implementations of realpath in glibc and musl. Thanks, this is very useful.
https://github.com/ifduyue/musl/blob/master/src/misc/realpath.c#L23-L27 I am going to share a way how to reproduce this issue. For now I have 2 containers: aarch64-unknown-linux-gnu and aarch64-gentoo-linux-musl, they are using same software versions, only one difference is libc. gcc /tmp/test.c -o /tmp/test && strace /tmp/test native result: openat(AT_FDCWD, "/proc/self/exe", O_RDONLY|O_PATH) = 3 readlinkat(AT_FDCWD, "/proc/self/fd/3", "/tmp/test", 512) = 9 write(2, "resolved path 0x560f71e2e2a0 gcc /tmp/test.c -o /tmp/test && QEMU_STRACE=1 /tmp/test aarch64-unknown-linux-gnu result: 1 openat(AT_FDCWD,"/proc/self/exe",O_RDONLY|O_PATH) = 3 1 readlinkat(-100,"/proc/self/fd/3",0x0000005501812a58,512) = -1 errno=2 (No such file or directory) resolved path 0x55000122a0 aarch64-gentoo-linux-musl result: 1 openat(AT_FDCWD,"/proc/self/exe",O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_PATH|0x20000) = 3 1 readlinkat(AT_FDCWD,"/proc/self/fd/3",0x0000005501811950,4095) = -1 errno=2 (No such file or directory) resolved path 0 We can see that open + readlinkat approach is working on native machine only. But there is some hand from the dark in qemu container that takes glibc realpath and returns right result. I think that this hand is qemu itself, but not sure. Funny picture =) https://i.imgur.com/s4SiKSL.jpg
Created attachment 653834 [details] test.c
I've just read qemu code a bit and can explain what happens. Please read the following code: https://github.com/qemu/qemu/blob/master/linux-user/syscall.c#L7485-L7507 Function "is_proc_myself" doesn't depend on anything related from qemu. You can just copy it to your test file and verify that: filename: "/proc/self/exe", entry: "exe" - passed filename: "/proc/<getpid>/exe", entry: "exe" - passed filename: "/proc/self/fd/<getpid>", entry: "exe" - failed It means that qemu today can't bypass readlink with filename "/proc/self/fd/<getpid>", so musl way won't work. Only legacy glibc way will work.
I've found a way how to implement exe fd mapping in easy way. if (is_proc_myself(pathname, "exe")) { int execfd = qemu_getauxval(AT_EXECFD); return execfd ? execfd : safe_openat(dirfd, exec_path, flags, mode); } You can just try to open open("/proc/self/exe", O_PATH) twice: native system will give you two different fds, but qemu will always return single fd. So we are sure that only one "/proc/self/fd/<global_execfd>" should be treated as "/proc/self/exe". I am going to think how to refactor "syscall_proc" staff and patch will be ready soon.
Created attachment 654506 [details, diff] incomplete patch
Unfortunatelly this patch is not enough to fix this issue: 1 openat(AT_FDCWD,"/proc/self/exe",O_RDONLY|O_PATH|0x20000) = 3 1 openat(AT_FDCWD,"/proc/self/exe",O_RDONLY|O_PATH|0x20000) = 3 1 fstat(3,0x0000005501812650) = -1 errno=9 (Bad file descriptor) 1 fcntl(3,F_GETFD) = -1 errno=9 (Bad file descriptor) 1 fstat(3,0x0000005501812650) = -1 errno=9 (Bad file descriptor) 1 fcntl(3,F_GETFD) = -1 errno=9 (Bad file descriptor) 1 readlinkat(AT_FDCWD,"/proc/self/exe",0x0000005501812b78,512) = 9 1 readlinkat(AT_FDCWD,"/proc/self/fd/3",0x0000005501812b78,512) = 9 1 readlinkat(AT_FDCWD,"/proc/self/fd/3",0x0000005501812b78,512) = 9 1 close(3) = -1 errno=9 (Bad file descriptor) 1 close(3) = -1 errno=9 (Bad file descriptor "openat" + "readlinkat" works fine, but "fstat" + "fcntl" ("close" too) is still broken. There is another bug here, it is related to "execfd" (equals "3" in example) behaviour.
Created attachment 654982 [details, diff] patch for qemu v5.0.0
Patch works fine for aarch64-gentoo-linux-musl, I will try to send it to qemu team.
(In reply to Andrew Aladjev from comment #32) > Patch works fine for aarch64-gentoo-linux-musl, I will try to send it to > qemu team. Great, had a look at your patch and it is white space damaged. You will want to clean that up before submitting it to QEMU
I've submited updated patch here, please review. https://lists.gnu.org/archive/html/qemu-devel/2020-08/msg03249.html
Created attachment 659016 [details, diff] final patch for qemu 5.1.0
Apologies for the "me too" comment, but I just hit precisely this problem. For the benefit of google I initial saw this as more "segfault running install under qemu-arm". However, after finding this bug I realised it's the more subtle. Thanks for working this solution. I can confirm it resolves my segfault for me (amd64 host with arm 32bit build chroot). I'm not clear if your patch has been accepted upstream? Can I +1 the possibility of adding this to the existing qemu-5.1.0 ebuild please? Thanks
Hello, I've send this patch to upstream, but it looks like it has been lost in other user patches. It looks like Joakim Tjernlund wanted to review patch, maybe we can assign issue to him. I think patch (for now) can be added to qemu-5.1.0 patches list, in this case we need to assign issue to Mike Gilbert. I have no permissions to assign issue, please help =).
(In reply to Andrew Aladjev from comment #37) > I think patch (for now) can be added to qemu-5.1.0 patches list, in this > case we need to assign issue to Mike Gilbert. I do not maintain qemu, but I will reassign this bug to its maintainer.
Please work with upstream to make it accepted and then we can backport it. Reading https://lists.gnu.org/archive/html/qemu-devel/2020-08/msg03628.html it needs some work.
I've send new series of patches here https://lists.gnu.org/archive/html/qemu-devel/2021-02/msg08088.html. Unfortunately qemu devel email system is overloaded, previous series of patches were not reviewed, I am sending it again. Please send invites to qemu developers for review our small patches.
Doesn't seem to have made it upstream. Maybe try resending and CC the linux-user maintainer? Seems to be "laurent AT vivier.eu" based on the MAINTAINERS file.
(In reply to Andrew Aladjev from comment #40) > I've send new series of patches here > https://lists.gnu.org/archive/html/qemu-devel/2021-02/msg08088.html. > Unfortunately qemu devel email system is overloaded, previous series of > patches were not reviewed, I am sending it again. Please send invites to > qemu developers for review our small patches. Ping Andrew.
