http://llvm.org/bugs/show_bug.cgi?id=19463
Bug ID: 19463
Summary: VLAIS - false positive
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: Common Code Generator Code
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
Compiling the kernel fails with
CC arch/x86/xen/mmu.o
/home/dl9pf/llvmlinux/targets/x86_64/src/linux/arch/x86/xen/mmu.c:1347:18:
error: fields must have a constant size: 'variable length array in structure'
extension will never be supported
DECLARE_BITMAP(mask, num_processors);
^
/home/dl9pf/llvmlinux/targets/x86_64/src/linux/include/linux/types.h:10:16:
note: expanded from macro 'DECLARE_BITMAP'
unsigned long name[BITS_TO_LONGS(bits)]
^
1 error generated.
include/linux/types.h:
######################
#define DECLARE_BITMAP(name,bits) \
unsigned long name[BITS_TO_LONGS(bits)]
include/linux/bitops.h:
#######################
#define BITS_TO_LONGS(nr) DIV_ROUND_UP(nr, BITS_PER_BYTE * sizeof(long))
include/linux/kernel.h:
#######################
#define DIV_ROUND_UP(n,d) (((n) + (d) - 1) / (d))
So DECLARE_BITMAP(mask, num_processors) should actually expand to a fixed -
but indeed platform-specific - size.
from mmu.i:
###########
static void xen_flush_tlb_others(const struct cpumask *cpus,
struct mm_struct *mm, unsigned long start,
unsigned long end)
{
struct {
struct mmuext_op op;
unsigned long mask[(((num_processors) + (8 * sizeof(long)) - 1) / (8 *
sizeof(long)))];
} *args;
struct multicall_space mcs;
I totally agree this looks and smells like VLAIS, but is it?
Can we deal with this in llvm/clang ?
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