Date: Wed, 1 May 2013 18:02:49 -0500 From: Stacey Son <sson@FreeBSD.org> To: freebsd-arch@freebsd.org Subject: A General or Miscellaneous Binary Image Activator Message-ID: <71BF89C0-13F9-41CA-9F7E-A3FDE11C2346@FreeBSD.org>
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Hi All, I have written a miscellaneous (or general) binary interpreter image = activator to support cross building mips64 ports using user mode qemu. = The source code can be found at: http://people.freebsd.org/~sson/imgact_binmisc/imgact_binmisc.h http://people.freebsd.org/~sson/imgact_binmisc/imgact_binmisc.c I just saw Nathan Whitehorn's posting 'LLVM Image Activator' on this = same list and hope we are not duplicating work. Like Nathan's this code = invokes a user-level interpreter or emulator when it recognizes the = magic bytes in a header of a binary. Unlike Nathan's it is much more = general purpose. It does this by using a magic field that may be up to = 'IBE_MAGIC_MAX' (or 256) bytes long , an offset value in the binary, = and, optionally, a bit mask field the same size as the magic field that = can mask out and ignore any of the bits in the magic. Therefore, it is = very flexible in supporting binary file types which I needed to figure = out the arch for ELF files. Of course, image activators have been a source for security issues. If = this or something like this is include in the kernel then I would = recommend it be optional. It has proven to be very useful for creating = a mixed arch cross build environment. This allows running things like = the cross compiler/toolchain and /bin/sh natively on the host system = which significantly helps performance. Using this, and the user mode = qemu port I have been working on, I have successfully cross built well = over 9000 mips64 packages from ports using an old amd64 athlon (FYI, see = https://wiki.freebsd.org/QemuUserModeHowTo for more information about = user mode qemu). It is configured from user space using sysctl(3). For example, the = following is for adding an activator that runs mips64 executables on an = amd64 host using "user mode" qemu: #include <sys/imgact_binmisc.h> #define MIPS64_ELF_MAGIC = "\x7f\x45\x4c\x46\x02\x02\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\= x00\x08" #define MIPS64_ELF_MASK = "\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xff\xfe\= xff\xff" ximgact_binmisc_entry_t xbe;=20 xbe.xbe_version =3D IBE_VERSION; xbe.xbe_command =3D IBC_ADD; xbe.xbe_flags =3D IBF_ENABLED | IBF_USE_MASK; strlcpy(xbe.xbe_name, "mips64elf", (IBE_NAME_MAX - 1)); strlcpy((xbe.xbe_interpreter, "/usr/local/bin/qemu-mips64", (MAXPATHLEN = -1)); xbe.xbe_offset =3D 0; xbe.xbe_size =3D sizeof(MIPS64_ELF_MAGIC) - 1; memcpy(xbe.xbe_magic, MIPS64_ELF_MAGIC, xbe.xbe_size); memcpy(xbe.xbe_mask, MIPS64_ELF_MASK, xbe.xbe_size); int ret =3D sysctlbyname("kern.binmisc", NULL, NULL, &xbe, = sizeof(xbe)); To disable/enable/delete the above entry in the kernel: xbe.xbe_version =3D IBE_VERSION; xbe.xbe_command =3D IBC_DISABLE; // or IBC_ENABLE or IBC_DELETE strlcpy(xbe.xbe_name, "mips64elf", (IBE_NAME_MAX - 1)); int ret =3D sysctlbyname("kern.binmisc", NULL, NULL, &xbe, sizeof(xbe)); To list all the interperter entries that are currently configured: ximagact_binmisc_list_t xbl; size_t xbe_size =3D sizeof(xbe); size_t xbl_size =3D sizeof(xbl); xbe.xbe_version =3D IBE_VERSION; xbe.xbe_command =3D IBC_LIST; sysctlbyname("kern.binmisc", &xbl, &xbl_size, &xbe, sizeof(xbe)); for(int i =3D 0; i < xbl.xbl_count; i++) { =09 xbe.xbe_version =3D IBE_VERSION; xbe.xbe_command =3D IBC_LOOKUP; =09 strlcpy(xbe.xbe_name, xbl.xbl_names[i], (IBE_NAME_MAX - 1)); =09 ret =3D sysctlbyname("kern.binmisc", &xbe, &xbe_size, &xbe, = sizeof(xbe)); =09 if (!ret) { // 'xbe' contains an interperter entry from the kernel = for=09 // the given 'xbl.xbl_name[i]' name. } } The sysctlbyname() calls above may return the following errors in = addition to the one from sysctl(3): [EINVAL] Invalid argment in the input ximgact_binmisc_entry_t = structure. [EEXIST] Interpreter entry for given name already exist in kernel = list.=20 [ENOMEM] Allocating memory in the kernel failed. [ENOENT] Interpreter entry for given name is not found. [ENOSPC] Attempted to exceed maximum number of entries = (IBE_MAX_ENTRIES). Of course, comments, questions, concerns, etc. are welcome. Best Regards, -stacey. sson@FreeBSD.org=
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