[PATCH] D38132: [Support] mapped_file_region: avoid tautological comparison.

[Zachary Turner via llvm-commits]

No, I just fail. I somehow thought the check was against the Offset
parameter.

Is changing the function to take a size_t an option?
On Thu, Sep 21, 2017 at 7:23 AM Roman Lebedev via Phabricator <
reviews at reviews.llvm.org> wrote:

> lebedev.ri added a comment.
>
> On Thu, Sep 21, 2017 at 4:56 PM, Zachary Turner <zturner at google.com>
> wrote:
>
> > I would move this logic into the init function.
>
> Do note that the check is comparing length (function param), and not Size
> (class member variable), even thought they currently have the same data
> type.
>
> > But there's another problem. mmap doesn't even accept a size_t, it
> accepts
> >  an off_t. Also, as far as I'm aware, off_t is a signed type. So perhaps
> you
> >  can compare against std::numeric_limits<off_t>::max() which will never
> be a
> >  tautological comparison
>
> Hmm, am i looking in the wrong place?
>
>   MMAP(3POSIX)
>                                                 POSIX Programmer's Manual
>
>                              MMAP(3POSIX)
>
>   PROLOG
>         This manual page is part of the POSIX Programmer's Manual.  The
> Linux implementation of this interface may differ (consult the
> corresponding Linux manual page for details of Linux behavior), or the
> interface may not be implemented on Linux.
>
>   NAME
>         mmap — map pages of memory
>
>   SYNOPSIS
>         #include <sys/mman.h>
>
>         void *mmap(void *addr, size_t len, int prot, int flags,
>             int fildes, off_t off);
>
>
>
>   MMAP(2)
>                                                Linux Programmer's Manual
>
>                                 MMAP(2)
>
>   NAME
>         mmap, munmap - map or unmap files or devices into memory
>
>   SYNOPSIS
>         #include <sys/mman.h>
>
>         void *mmap(void *addr, size_t length, int prot, int flags,
>                    int fd, off_t offset);
>         int munmap(void *addr, size_t length);
>
> `mman.h`:
>
>   #ifndef __USE_FILE_OFFSET64
>   extern void *mmap (void *__addr, size_t __len, int __prot,
>                    int __flags, int __fd, __off_t __offset) __THROW;
>   #else
>   # ifdef __REDIRECT_NTH
>   extern void * __REDIRECT_NTH (mmap,
>                               (void *__addr, size_t __len, int __prot,
>                                int __flags, int __fd, __off64_t __offset),
>                               mmap64);
>   # else
>   #  define mmap mmap64
>   # endif
>   #endif
>
>
> Repository:
>   rL LLVM
>
> https://reviews.llvm.org/D38132
>
>
>
>
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