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    Subject[PATCH 04/14] lib/vsprintf.c: expand field_width to 24 bits
    Date
    Maurizio Lombardi reported a problem [1] with the %pb extension: It
    doesn't work for sufficiently large bitmaps, since the size is stashed
    in the field_width field of the struct printf_spec, which is currently
    an s16. Concretely, this manifested itself in
    /sys/bus/pseudo/drivers/scsi_debug/map being empty, since the bitmap
    printer got a size of 0, which is the 16 bit truncation of the actual
    bitmap size.

    We do want to keep struct printf_spec at 8 bytes so that it can
    cheaply be passed by value. The qualifier field is only used for
    internal bookkeeping in format_decode, so we might as well use a local
    variable for that. This gives us an additional 8 bits, which we can
    then use for the field width.

    To stay in 8 bytes, we need to do a little rearranging and make the
    type member a bitfield as well. For consistency, change all the
    members to bit fields. gcc doesn't generate much worse code with these
    changes (in fact, bloat-o-meter says we save 300 bytes - which I think
    is a little surprising).

    I didn't find a BUILD_BUG/compiletime_assertion/... which would work
    outside function context, so for now I just open-coded it.

    [1] http://thread.gmane.org/gmane.linux.kernel/2034835

    Reported-by: Maurizio Lombardi <mlombard@redhat.com>
    Cc: Tejun Heo <tj@kernel.org>
    Cc: Joe Perches <joe@perches.com>
    Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
    ---
    lib/vsprintf.c | 41 +++++++++++++++++++++--------------------
    1 file changed, 21 insertions(+), 20 deletions(-)

    diff --git a/lib/vsprintf.c b/lib/vsprintf.c
    index 63ca52366049..01c3aa638582 100644
    --- a/lib/vsprintf.c
    +++ b/lib/vsprintf.c
    @@ -380,13 +380,13 @@ enum format_type {
    };

    struct printf_spec {
    - u8 type; /* format_type enum */
    - u8 flags; /* flags to number() */
    - u8 base; /* number base, 8, 10 or 16 only */
    - u8 qualifier; /* number qualifier, one of 'hHlLtzZ' */
    - s16 field_width; /* width of output field */
    - s16 precision; /* # of digits/chars */
    -};
    + unsigned int type:8; /* format_type enum */
    + signed int field_width:24; /* width of output field */
    + unsigned int flags:8; /* flags to number() */
    + unsigned int base:8; /* number base, 8, 10 or 16 only */
    + signed int precision:16; /* # of digits/chars */
    +} __packed;
    +extern char __check_printf_spec[1-2*(sizeof(struct printf_spec) != 8)];

    static noinline_for_stack
    char *number(char *buf, char *end, unsigned long long num,
    @@ -1641,6 +1641,7 @@ static noinline_for_stack
    int format_decode(const char *fmt, struct printf_spec *spec)
    {
    const char *start = fmt;
    + char qualifier;

    /* we finished early by reading the field width */
    if (spec->type == FORMAT_TYPE_WIDTH) {
    @@ -1723,16 +1724,16 @@ precision:

    qualifier:
    /* get the conversion qualifier */
    - spec->qualifier = -1;
    + qualifier = 0;
    if (*fmt == 'h' || _tolower(*fmt) == 'l' ||
    _tolower(*fmt) == 'z' || *fmt == 't') {
    - spec->qualifier = *fmt++;
    - if (unlikely(spec->qualifier == *fmt)) {
    - if (spec->qualifier == 'l') {
    - spec->qualifier = 'L';
    + qualifier = *fmt++;
    + if (unlikely(qualifier == *fmt)) {
    + if (qualifier == 'l') {
    + qualifier = 'L';
    ++fmt;
    - } else if (spec->qualifier == 'h') {
    - spec->qualifier = 'H';
    + } else if (qualifier == 'h') {
    + qualifier = 'H';
    ++fmt;
    }
    }
    @@ -1789,19 +1790,19 @@ qualifier:
    return fmt - start;
    }

    - if (spec->qualifier == 'L')
    + if (qualifier == 'L')
    spec->type = FORMAT_TYPE_LONG_LONG;
    - else if (spec->qualifier == 'l') {
    + else if (qualifier == 'l') {
    BUILD_BUG_ON(FORMAT_TYPE_ULONG + SIGN != FORMAT_TYPE_LONG);
    spec->type = FORMAT_TYPE_ULONG + (spec->flags & SIGN);
    - } else if (_tolower(spec->qualifier) == 'z') {
    + } else if (_tolower(qualifier) == 'z') {
    spec->type = FORMAT_TYPE_SIZE_T;
    - } else if (spec->qualifier == 't') {
    + } else if (qualifier == 't') {
    spec->type = FORMAT_TYPE_PTRDIFF;
    - } else if (spec->qualifier == 'H') {
    + } else if (qualifier == 'H') {
    BUILD_BUG_ON(FORMAT_TYPE_UBYTE + SIGN != FORMAT_TYPE_BYTE);
    spec->type = FORMAT_TYPE_UBYTE + (spec->flags & SIGN);
    - } else if (spec->qualifier == 'h') {
    + } else if (qualifier == 'h') {
    BUILD_BUG_ON(FORMAT_TYPE_USHORT + SIGN != FORMAT_TYPE_SHORT);
    spec->type = FORMAT_TYPE_USHORT + (spec->flags & SIGN);
    } else {
    --
    2.6.1


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