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Message-Id: <20090922175008.422945e5.akpm@linux-foundation.org>
Date: Tue, 22 Sep 2009 17:50:08 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Roland McGrath <roland@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
linux-kernel@...r.kernel.org,
Johannes Berg <johannes@...solutions.net>,
Vegard Nossum <vegard.nossum@...il.com>
Subject: Re: [PATCH] kmemcheck: clean up kmemcheck_annotate_bitfield
On Tue, 22 Sep 2009 17:13:01 -0700 (PDT) Roland McGrath <roland@...hat.com> wrote:
> The commit 181f7c5dd3832763bdf2756b6d2d8a49bdf12791 change traded a
> style warning from sparse for a syntax warning from the real compiler
> (and perhaps an error with compilers old enough). The use of a local
> variable inside BUILD_BUG_ON() is pretty questionable too, though it
> works with the compiler's constant-folding in practice.
>
> This change cleans it all up a little more sanely.
> The details are self-explanatory.
>
> Signed-off-by: Roland McGrath <roland@...hat.com>
> CC: Johannes Berg <johannes@...solutions.net>
> CC: Vegard Nossum <vegard.nossum@...il.com>
> ---
> include/linux/kmemcheck.h | 14 ++++++--------
> 1 files changed, 6 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/kmemcheck.h b/include/linux/kmemcheck.h
> index c800660..9e2c5f4 100644
> --- a/include/linux/kmemcheck.h
> +++ b/include/linux/kmemcheck.h
> @@ -143,16 +143,14 @@ static inline bool kmemcheck_is_obj_initialized(unsigned long addr, size_t size)
> #define kmemcheck_bitfield_end(name) \
> int name##_end[0];
>
> +#define kmemcheck_bitfield_stretch(ptr, name) \
> + ((long) &(ptr)->name##_end - (long) &(ptr)->name##_begin)
> +
> #define kmemcheck_annotate_bitfield(ptr, name) \
> do { \
> - if (!ptr) \
> - break; \
> - \
> - int _n = (long) &((ptr)->name##_end) \
> - - (long) &((ptr)->name##_begin); \
> - BUILD_BUG_ON(_n < 0); \
> - \
> - kmemcheck_mark_initialized(&((ptr)->name##_begin), _n); \
> + BUILD_BUG_ON(kmemcheck_bitfield_stretch(ptr, name) < 0);\
> + kmemcheck_mark_initialized(&(ptr)->name##_begin, \
> + kmemcheck_bitfield_stretch(ptr, name)); \
> } while (0)
>
> #define kmemcheck_annotate_variable(var) \
I just sent Linus the simple version:
--- a/include/linux/kmemcheck.h~include-linux-kmemcheckh-fix-a-trillion-warnings
+++ a/include/linux/kmemcheck.h
@@ -145,10 +145,12 @@ static inline bool kmemcheck_is_obj_init
#define kmemcheck_annotate_bitfield(ptr, name) \
do { \
+ int _n; \
+ \
if (!ptr) \
break; \
\
- int _n = (long) &((ptr)->name##_end) \
+ _n = (long) &((ptr)->name##_end) \
- (long) &((ptr)->name##_begin); \
BUILD_BUG_ON(_n < 0); \
\
_
That BUILD_BUG_ON() is just wrong, but nobody knew that because the
present version of BUILD_BUG_ON() silently does nothing if passed an
expression which isn't a compile-time constant. This was all fixed in
the just-sent
build_bug_on-fix-it-and-a-couple-of-bogus-uses-of-it.patch:
From: "Jan Beulich" <JBeulich@...ell.com>
gcc permitting variable length arrays makes the current construct used for
BUILD_BUG_ON() useless, as that doesn't produce any diagnostic if the
controlling expression isn't really constant. Instead, this patch makes
it so that a bit field gets used here. Consequently, those uses where the
condition isn't really constant now also need fixing.
Note that in the gfp.h, kmemcheck.h, and virtio_config.h cases
MAYBE_BUILD_BUG_ON() really just serves documentation purposes - even if
the expression is compile time constant (__builtin_constant_p() yields
true), the array is still deemed of variable length by gcc, and hence the
whole expression doesn't have the intended effect.
[akpm@...ux-foundation.org: make arch/sparc/include/asm/vio.h compile]
[akpm@...ux-foundation.org: more nonsensical assertions in tpm.c..]
Signed-off-by: Jan Beulich <jbeulich@...ell.com>
Cc: Andi Kleen <andi@...stfloor.org>
Cc: Rusty Russell <rusty@...tcorp.com.au>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: "David S. Miller" <davem@...emloft.net>
Cc: Rajiv Andrade <srajiv@...ux.vnet.ibm.com>
Cc: Mimi Zohar <zohar@...ibm.com>
Cc: James Morris <jmorris@...ei.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---
arch/sparc/include/asm/vio.h | 2 +-
drivers/char/tpm/tpm.c | 4 ++--
drivers/net/niu.c | 2 +-
include/linux/gfp.h | 2 +-
include/linux/kernel.h | 8 ++++++--
include/linux/kmemcheck.h | 2 +-
include/linux/virtio_config.h | 3 +--
7 files changed, 13 insertions(+), 10 deletions(-)
diff -puN arch/sparc/include/asm/vio.h~build_bug_on-fix-it-and-a-couple-of-bogus-uses-of-it arch/sparc/include/asm/vio.h
--- a/arch/sparc/include/asm/vio.h~build_bug_on-fix-it-and-a-couple-of-bogus-uses-of-it
+++ a/arch/sparc/include/asm/vio.h
@@ -258,7 +258,7 @@ static inline void *vio_dring_entry(stru
static inline u32 vio_dring_avail(struct vio_dring_state *dr,
unsigned int ring_size)
{
- BUILD_BUG_ON(!is_power_of_2(ring_size));
+ MAYBE_BUILD_BUG_ON(!is_power_of_2(ring_size));
return (dr->pending -
((dr->prod - dr->cons) & (ring_size - 1)));
diff -puN drivers/char/tpm/tpm.c~build_bug_on-fix-it-and-a-couple-of-bogus-uses-of-it drivers/char/tpm/tpm.c
--- a/drivers/char/tpm/tpm.c~build_bug_on-fix-it-and-a-couple-of-bogus-uses-of-it
+++ a/drivers/char/tpm/tpm.c
@@ -696,7 +696,7 @@ int __tpm_pcr_read(struct tpm_chip *chip
cmd.header.in = pcrread_header;
cmd.params.pcrread_in.pcr_idx = cpu_to_be32(pcr_idx);
- BUILD_BUG_ON(cmd.header.in.length > READ_PCR_RESULT_SIZE);
+ BUG_ON(cmd.header.in.length > READ_PCR_RESULT_SIZE);
rc = transmit_cmd(chip, &cmd, cmd.header.in.length,
"attempting to read a pcr value");
@@ -760,7 +760,7 @@ int tpm_pcr_extend(u32 chip_num, int pcr
return -ENODEV;
cmd.header.in = pcrextend_header;
- BUILD_BUG_ON(be32_to_cpu(cmd.header.in.length) > EXTEND_PCR_SIZE);
+ BUG_ON(be32_to_cpu(cmd.header.in.length) > EXTEND_PCR_SIZE);
cmd.params.pcrextend_in.pcr_idx = cpu_to_be32(pcr_idx);
memcpy(cmd.params.pcrextend_in.hash, hash, TPM_DIGEST_SIZE);
rc = transmit_cmd(chip, &cmd, cmd.header.in.length,
diff -puN drivers/net/niu.c~build_bug_on-fix-it-and-a-couple-of-bogus-uses-of-it drivers/net/niu.c
--- a/drivers/net/niu.c~build_bug_on-fix-it-and-a-couple-of-bogus-uses-of-it
+++ a/drivers/net/niu.c
@@ -5615,7 +5615,7 @@ static void niu_init_tx_mac(struct niu *
/* The XMAC_MIN register only accepts values for TX min which
* have the low 3 bits cleared.
*/
- BUILD_BUG_ON(min & 0x7);
+ BUG_ON(min & 0x7);
if (np->flags & NIU_FLAGS_XMAC)
niu_init_tx_xmac(np, min, max);
diff -puN include/linux/gfp.h~build_bug_on-fix-it-and-a-couple-of-bogus-uses-of-it include/linux/gfp.h
--- a/include/linux/gfp.h~build_bug_on-fix-it-and-a-couple-of-bogus-uses-of-it
+++ a/include/linux/gfp.h
@@ -220,7 +220,7 @@ static inline enum zone_type gfp_zone(gf
((1 << ZONES_SHIFT) - 1);
if (__builtin_constant_p(bit))
- BUILD_BUG_ON((GFP_ZONE_BAD >> bit) & 1);
+ MAYBE_BUILD_BUG_ON((GFP_ZONE_BAD >> bit) & 1);
else {
#ifdef CONFIG_DEBUG_VM
BUG_ON((GFP_ZONE_BAD >> bit) & 1);
diff -puN include/linux/kernel.h~build_bug_on-fix-it-and-a-couple-of-bogus-uses-of-it include/linux/kernel.h
--- a/include/linux/kernel.h~build_bug_on-fix-it-and-a-couple-of-bogus-uses-of-it
+++ a/include/linux/kernel.h
@@ -678,13 +678,17 @@ struct sysinfo {
};
/* Force a compilation error if condition is true */
-#define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)]))
+#define BUILD_BUG_ON(condition) ((void)BUILD_BUG_ON_ZERO(condition))
+
+/* Force a compilation error if condition is constant and true */
+#define MAYBE_BUILD_BUG_ON(cond) ((void)sizeof(char[1 - 2 * !!(cond)]))
/* Force a compilation error if condition is true, but also produce a
result (of value 0 and type size_t), so the expression can be used
e.g. in a structure initializer (or where-ever else comma expressions
aren't permitted). */
-#define BUILD_BUG_ON_ZERO(e) (sizeof(char[1 - 2 * !!(e)]) - 1)
+#define BUILD_BUG_ON_ZERO(e) (sizeof(struct { int:-!!(e); }))
+#define BUILD_BUG_ON_NULL(e) ((void *)sizeof(struct { int:-!!(e); }))
/* Trap pasters of __FUNCTION__ at compile-time */
#define __FUNCTION__ (__func__)
diff -puN include/linux/kmemcheck.h~build_bug_on-fix-it-and-a-couple-of-bogus-uses-of-it include/linux/kmemcheck.h
--- a/include/linux/kmemcheck.h~build_bug_on-fix-it-and-a-couple-of-bogus-uses-of-it
+++ a/include/linux/kmemcheck.h
@@ -152,7 +152,7 @@ static inline bool kmemcheck_is_obj_init
\
_n = (long) &((ptr)->name##_end) \
- (long) &((ptr)->name##_begin); \
- BUILD_BUG_ON(_n < 0); \
+ MAYBE_BUILD_BUG_ON(_n < 0); \
\
kmemcheck_mark_initialized(&((ptr)->name##_begin), _n); \
} while (0)
diff -puN include/linux/virtio_config.h~build_bug_on-fix-it-and-a-couple-of-bogus-uses-of-it include/linux/virtio_config.h
--- a/include/linux/virtio_config.h~build_bug_on-fix-it-and-a-couple-of-bogus-uses-of-it
+++ a/include/linux/virtio_config.h
@@ -109,8 +109,7 @@ static inline bool virtio_has_feature(co
unsigned int fbit)
{
/* Did you forget to fix assumptions on max features? */
- if (__builtin_constant_p(fbit))
- BUILD_BUG_ON(fbit >= 32);
+ MAYBE_BUILD_BUG_ON(fbit >= 32);
if (fbit < VIRTIO_TRANSPORT_F_START)
virtio_check_driver_offered_feature(vdev, fbit);
_
--
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