lib/vsprintf.c: expand field_width to 24 bits

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>

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index c537a73..c09182e 100644 (file)
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -383,13 +383,12 @@ 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;
 
 static noinline_for_stack
 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;
        bool is_zero = num == 0LL;
 
+       BUILD_BUG_ON(sizeof(struct printf_spec) != 8);
+
        /* locase = 0 or 0x20. ORing digits or letters with 'locase'
         * produces same digits or (maybe lowercased) letters */
        locase = (spec.flags & SMALL);
@@ -1670,6 +1671,7 @@ 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) {
@@ -1752,16 +1754,16 @@ 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;
                        }
                }
@@ -1818,19 +1820,19 @@ 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 {