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    [ARM] safer handling of syscall table padding · fa1b4f91
    Al Viro 提交于
    ARM entry-common.S needs to know syscall table size; in itself that would
    not be a problem, but there's an additional constraint - some of the
    instructions using it want a constant that would be a multiple of 4.
    So we have to pad syscall table with sys_ni_syscall and that's where
    the trouble begins.  .rept pseudo-op wants a constant expression for
    number of repetitions and subtraction of two labels (before and after
    syscall table) doesn't always get simplified to constant early enough
    for .rept.  If labels end up in different frags, we lose.  And while
    the frag size is large enough (slightly below 4Kb), the syscall table
    is about 1/3 of that.  We used to get away with that, but the recent
    changes had been enough to trigger the breakage.
    
    Proper fix is simple: have a macro (CALL(x)) to populate the table
    instead of using explicit .long x and the first time we include calls.S
    have it defined to .equ NR_syscalls,NR_syscalls+1.  Then we can find
    the proper amount of padding on the first inclusion simply by looking
    at NR_syscalls at that time.  And that will be constant, no matter what.
    
    Moreover, the same trick kills the need of having an estimate of padded
    NR_syscalls - it will be calculated for free at the same time.
    Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
    Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>
    fa1b4f91
entry-common.S 8.9 KB