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lib/vsprintf.c: expand field_width to 24 bits

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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

[akpm@linux-foundation.org: avoid open-coded BUILD_BUG_ON]
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Reported-by: Maurizio Lombardi <mlombard@redhat.com>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Joe Perches <joe@perches.com>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Rasmus Villemoes 2016-01-15 16:58:37 -08:00 committed by Linus Torvalds
parent 34fc8b9076
commit d048419311
1 changed files with 22 additions and 20 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

42
lib/vsprintf.c
View file

@ -383,13 +383,12 @@ enum format_type {
}; };
struct printf_spec { struct printf_spec {
u8 type; /* format_type enum */ unsigned int type:8; /* format_type enum */
u8 flags; /* flags to number() */ signed int field_width:24; /* width of output field */
u8 base; /* number base, 8, 10 or 16 only */ unsigned int flags:8; /* flags to number() */
u8 qualifier; /* number qualifier, one of 'hHlLtzZ' */ unsigned int base:8; /* number base, 8, 10 or 16 only */
s16 field_width; /* width of output field */ signed int precision:16; /* # of digits/chars */
s16 precision; /* # of digits/chars */ } __packed;
};
static noinline_for_stack static noinline_for_stack
char *number(char *buf, char *end, unsigned long long num, char *number(char *buf, char *end, unsigned long long num,
@ -403,6 +402,8 @@ char *number(char *buf, char *end, unsigned long long num,
int i; int i;
bool is_zero = num == 0LL; bool is_zero = num == 0LL;
BUILD_BUG_ON(sizeof(struct printf_spec) != 8);
/* locase = 0 or 0x20. ORing digits or letters with 'locase' /* locase = 0 or 0x20. ORing digits or letters with 'locase'
* produces same digits or (maybe lowercased) letters */ * produces same digits or (maybe lowercased) letters */
locase = (spec.flags & SMALL); locase = (spec.flags & SMALL);
@ -1670,6 +1671,7 @@ static noinline_for_stack
int format_decode(const char *fmt, struct printf_spec *spec) int format_decode(const char *fmt, struct printf_spec *spec)
{ {
const char *start = fmt; const char *start = fmt;
char qualifier;
/* we finished early by reading the field width */ /* we finished early by reading the field width */
if (spec->type == FORMAT_TYPE_WIDTH) { if (spec->type == FORMAT_TYPE_WIDTH) {
@ -1752,16 +1754,16 @@ int format_decode(const char *fmt, struct printf_spec *spec)
qualifier: qualifier:
/* get the conversion qualifier */ /* get the conversion qualifier */
spec->qualifier = -1; qualifier = 0;
if (*fmt == 'h' || _tolower(*fmt) == 'l' || if (*fmt == 'h' || _tolower(*fmt) == 'l' ||
_tolower(*fmt) == 'z' || *fmt == 't') { _tolower(*fmt) == 'z' || *fmt == 't') {
spec->qualifier = *fmt++; qualifier = *fmt++;
if (unlikely(spec->qualifier == *fmt)) { if (unlikely(qualifier == *fmt)) {
if (spec->qualifier == 'l') { if (qualifier == 'l') {
spec->qualifier = 'L'; qualifier = 'L';
++fmt; ++fmt;
} else if (spec->qualifier == 'h') { } else if (qualifier == 'h') {
spec->qualifier = 'H'; qualifier = 'H';
++fmt; ++fmt;
} }
} }
@ -1818,19 +1820,19 @@ int format_decode(const char *fmt, struct printf_spec *spec)
return fmt - start; return fmt - start;
} }
if (spec->qualifier == 'L') if (qualifier == 'L')
spec->type = FORMAT_TYPE_LONG_LONG; 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); BUILD_BUG_ON(FORMAT_TYPE_ULONG + SIGN != FORMAT_TYPE_LONG);
spec->type = FORMAT_TYPE_ULONG + (spec->flags & SIGN); 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; spec->type = FORMAT_TYPE_SIZE_T;
} else if (spec->qualifier == 't') { } else if (qualifier == 't') {
spec->type = FORMAT_TYPE_PTRDIFF; spec->type = FORMAT_TYPE_PTRDIFF;
} else if (spec->qualifier == 'H') { } else if (qualifier == 'H') {
BUILD_BUG_ON(FORMAT_TYPE_UBYTE + SIGN != FORMAT_TYPE_BYTE); BUILD_BUG_ON(FORMAT_TYPE_UBYTE + SIGN != FORMAT_TYPE_BYTE);
spec->type = FORMAT_TYPE_UBYTE + (spec->flags & SIGN); 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); BUILD_BUG_ON(FORMAT_TYPE_USHORT + SIGN != FORMAT_TYPE_SHORT);
spec->type = FORMAT_TYPE_USHORT + (spec->flags & SIGN); spec->type = FORMAT_TYPE_USHORT + (spec->flags & SIGN);
} else { } else {