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 <mlomb...@redhat.com> Cc: Andy Shevchenko <andy.shevche...@gmail.com> Cc: Joe Perches <j...@perches.com> Acked-by: Tejun Heo <t...@kernel.org> Signed-off-by: Rasmus Villemoes <li...@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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
