The patch titled
BUILD_BUG_ON(): fix it and a couple of bogus uses of it
has been added to the -mm tree. Its filename is
build_bug_on-fix-it-and-a-couple-of-bogus-uses-of-it.patch
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*** Remember to use Documentation/SubmitChecklist when testing your code ***
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out what to do about this
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: BUILD_BUG_ON(): fix it and a couple of bogus uses of it
From: "Jan Beulich" <JBeulich@xxxxxxxxxx>
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.
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>
Cc: Andi Kleen <andi@xxxxxxxxxxxxxx>
Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/char/tpm/tpm.c | 2 --
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 +--
6 files changed, 10 insertions(+), 9 deletions(-)
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 +696,6 @@ 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);
rc = transmit_cmd(chip, &cmd, cmd.header.in.length,
"attempting to read a pcr value");
@@ -760,7 +759,6 @@ 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);
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
@@ -140,7 +140,7 @@ static inline void kmemcheck_mark_initia
do if (ptr) { \
int _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);
_
Patches currently in -mm which might be from JBeulich@xxxxxxxxxx are
linux-next.patch
memory-hotplug-fix-updating-of-num_physpages-for-hot-plugged-memory.patch
mm-replace-various-uses-of-num_physpages-by-totalram_pages.patch
mm-dont-use-alloc_bootmem_low-where-not-strictly-needed.patch
mm-also-use-alloc_large_system_hash-for-the-pid-hash-table.patch
build_bug_on-fix-it-and-a-couple-of-bogus-uses-of-it.patch
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