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Message-ID: <877fnq2jc0.fsf@rasmusvillemoes.dk>
Date: Wed, 16 Sep 2015 22:35:43 +0200
From: Rasmus Villemoes <linux@...musvillemoes.dk>
To: Tejun Heo <tj@...nel.org>
Cc: Maurizio Lombardi <mlombard@...hat.com>, joe@...ches.com,
linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 0/3] fix *pbl format support
On Wed, Sep 16 2015, Tejun Heo <tj@...nel.org> wrote:
>
> I suppose (2) could work too but we really should strive to provide
> something convenient to print[fk] users. The balance here is pretty
> one-sided.
>
I just remembered: I noticed a while ago that the qualifier member is
only used inside format_decode (in the end, the information is folded
into the type member), so one might as well use a local variable for
that. This gives option (3): Make field_width a 24 bit bitfield. I think
that should be sufficient for any realistic bitmap that one would
print. The patch is also rather small. Surprisingly, bloat-o-meter even
says that it's also a net win in code size:
add/remove: 18/16 grow/shrink: 3/2 up/down: 5551/-5775 (-224)
(the huge absolute numbers are due to stuff like
pointer - 1148 +1148
pointer.isra 1116 - -1116
so the functions haven't actually changed that much). I'll have to check
how this can be (smaller might still be worse), but at least it doesn't
seem to be a catastrophe in terms of .text bloat.
[Grr, why don't we have a way to do a compile-time assert outside
function context?]
Only compile-tested.
From: Rasmus Villemoes <linux@...musvillemoes.dk>
Date: Wed, 16 Sep 2015 22:06:14 +0200
Subject: [RFC] lib/vsprintf.c: expand field_width to 24 bits
Maurizio Lombardi reported a problem 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.
Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
---
lib/vsprintf.c | 33 +++++++++++++++++----------------
1 file changed, 17 insertions(+), 16 deletions(-)
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 95cd63b43b99..cce2a780a82e 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 type:8; /* format_type enum */
+ s32 field_width:24; /* width of output field */
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 */
};
+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,
@@ -1633,6 +1633,7 @@ 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) {
@@ -1715,16 +1716,16 @@ 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;
}
}
@@ -1781,19 +1782,19 @@ 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 {
--
2.1.3
--
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