• akpm@osdl.org's avatar
    [PATCH] N32 sigset and __COMPAT_ENDIAN_SWAP__ · 838cd153
    akpm@osdl.org authored
    I'm testing glibc on MIPS64, little-endian, N32, O32 and N64 multilibs.
    
    Among the NPTL test failures seen are some arising from sigsuspend problems
    for N32: it blocks the wrong signals, so SIGCANCEL (SIGRTMIN) is blocked
    despite glibc's carefully excluding it from sets of signals to block.
    Specifically, testing suggests it blocks signal N^32 instead of signal N,
    so (in the example tested) blocking SIGUSR1 (17) blocks signal 49 instead.
    
    glibc's sigset_t uses an array of unsigned long, as does the kernel.
    In both cases, signal N+1 is represented as
    (1UL << (N % (8 * sizeof (unsigned long)))) in word number
    (N / (8 * sizeof (unsigned long))).
    
    Thus the N32 glibc uses an array of 32-bit words and the N64 kernel uses an
    array of 64-bit words.  For little-endian, the layout is the same, with
    signals 1-32 in the first 4 bytes, signals 33-64 in the second, etc.; for
    big-endian, userspace has that layout while in the kernel each 8 bytes have
    the two halves swapped from the userspace layout.
    
    The N32 sigsuspend syscall uses sigset_from_compat to convert the userspace
    sigset to kernel format.  If __COMPAT_ENDIAN_SWAP__ is *not* set, this uses
    logic of the form
    
      set->sig[0] = compat->sig[0] | (((long)compat->sig[1]) << 32 )
    
    to convert the userspace sigset to a kernel one.  This looks correct to me
    for both big and little endian, given that in userspace compat->sig[1] will
    represent signals 33-64, and so will the high 32 bits of set->sig[0] in the
    kernel.  If however __COMPAT_ENDIAN_SWAP__ *is* set, as it is for
    __MIPSEL__, it uses
    
      set->sig[0] = compat->sig[1] | (((long)compat->sig[0]) << 32 );
    
    which seems incorrect for both big and little endian, and would
    explain the observed symptoms.
    
    This code is the only use of __COMPAT_ENDIAN_SWAP__, so if incorrect
    then that macro serves no purpose, in which case something like the
    following patch would seem appropriate to remove it.
    Signed-off-by: default avatarJoseph Myers <joseph@codesourcery.com>
    Signed-off-by: default avatarRalf Baechle <ralf@linux-mips.org>
    Cc: Arnd Bergmann <arnd@arndb.de>
    Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
    838cd153
compat.c 24.3 KB