Messages in this thread Patch in this message | | | Date | Tue, 18 Aug 2009 16:59:25 +0100 | From | "Jan Beulich" <> | Subject | [PATCH] fix BUILD_BUG_ON() and a couple of bogus uses of it |
| |
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@novell.com>
--- 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(-)
--- linux-2.6.31-rc6/drivers/char/tpm/tpm.c 2009-08-18 15:31:17.000000000 +0200 +++ 2.6.31-rc6-build-bug-on/drivers/char/tpm/tpm.c 2009-08-17 15:21:11.000000000 +0200 @@ -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, --- linux-2.6.31-rc6/drivers/net/niu.c 2009-08-18 15:31:34.000000000 +0200 +++ 2.6.31-rc6-build-bug-on/drivers/net/niu.c 2009-08-17 15:21:11.000000000 +0200 @@ -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); --- linux-2.6.31-rc6/include/linux/gfp.h 2009-08-18 15:31:54.000000000 +0200 +++ 2.6.31-rc6-build-bug-on/include/linux/gfp.h 2009-08-17 15:21:11.000000000 +0200 @@ -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); --- linux-2.6.31-rc6/include/linux/kernel.h 2009-08-18 15:31:55.000000000 +0200 +++ 2.6.31-rc6-build-bug-on/include/linux/kernel.h 2009-08-17 15:21:11.000000000 +0200 @@ -675,13 +675,17 @@ 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__) --- linux-2.6.31-rc6/include/linux/kmemcheck.h 2009-08-18 15:31:55.000000000 +0200 +++ 2.6.31-rc6-build-bug-on/include/linux/kmemcheck.h 2009-08-17 15:21:11.000000000 +0200 @@ -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) --- linux-2.6.31-rc6/include/linux/virtio_config.h 2009-08-18 15:31:55.000000000 +0200 +++ 2.6.31-rc6-build-bug-on/include/linux/virtio_config.h 2009-08-17 15:21:11.000000000 +0200 @@ -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);
| |