lfcompile(5)
NAME
lfcompile - large file compilation environment for 32-bit
applications
DESCRIPTION
All 64-bit applications can manipulate large files by
default. The methods described on this page allow 32-bit
applications to manipulate large files.
In the large file compilation environment, source interfaces
are bound to appropriate 64-bit functions, structures, and
types. Compiling in this environment allows 32-bit applica-
tions to access files whose size is greater than or equal to
2 Gbyte ( 2**31 bytes).
Each interface named xxx() that needs to access 64-bit enti-
ties to access large files maps to a xxx64() call in the
resulting binary. All relevant data types are defined to be
of correct size (for example, off_t has a typedef definition
for a 64-bit entity).
An application compiled in this environment is able to use
the xxx() source interfaces to access both large and small
files, rather than having to explicitly utilize the transi-
tional xxx64() interface calls to access large files. See
the lfcompile64(5) manual page for information regarding the
transitional compilation environment.
Applications can be compiled in the large file compilation
environment by using the following methods:
o Use the getconf(1) utility with one or more of the
arguments listed in the table below. This method is
recommended for portable applications.
____________________________________________________________
| argument | purpose |
| LFS_CFLAGS | obtain compilation flags necessary to|
| | enable the large file compilation|
| | environment |
| LFS_LDFLAGS | obtain link editor options |
| LFS_LIBS | obtain link library names |
| LFS_LINTFLAGS | obtain lint options |
|__________________|________________________________________|
o Set the compile-time flag _FILE_OFFSET_BITS to 64
before including any headers. Applications may combine
objects produced in the large file compilation
environment with objects produced in the transitional
compilation environment, but must be careful with
respect to interoperability between those objects.
Applications should not declare global variables of
types whose sizes change between compilation environ-
ments.
Access to Additional Large File Interfaces
The fseek() and ftell() functions do not map to functions
named fseek64() and ftell64(); rather, the large file addi-
tions fseeko() and ftello(), have functionality identical to
fseek() and ftell() and do map to the 64-bit functions
fseeko64() and ftello64(). Applications wishing to access
large files should use fseeko() and ftello() in place of
fseek() and ftell(). See the fseek(3C) and ftell(3C) manual
pages for information about fseeko() and ftello().
Applications wishing to access fseeko() and ftello() as
well as the POSIX and X/Open specification-conforming inter-
faces should define the macro _LARGEFILE_SOURCE to be 1 and
set whichever feature test macros are appropriate to obtain
the desired environment (see standards(5)).
EXAMPLES
In the following examples, the large file compilation
environment is accessed by invoking the getconf utility with
one of the arguments listed in the table above. The addi-
tional large file interfaces are accessed by specifying
-D_LARGEFILE_SOURCE.
The examples that use the form of command substitution
specifying the command within parentheses preceded by a dol-
lar sign can be executed only in a POSIX-conforming shell
such as the Korn Shell (see ksh(1)). In a shell that is not
POSIX-conforming, such as the Bourne Shell (see sh(1)) and
the C Shell (see csh(1)), the getconf calls must be enclosed
within grave accent marks, as shown in the second example.
Example 1: An example of compiling a program with a "large"
off_t, and that uses fseeko(), ftello(), and yacc(1)
$ c89 -D_LARGEFILE_SOURCE \
-D_FILE_OFFSET_BITS=64 -o foo \
$(getconf LFS_CFLAGS) y.tab.c b.o \
$(getconf LFS_LDFLAGS) \
-ly $(getconf LFS_LIBS)
Example 2: An example of compiling a program with a "large"
off_t that does not use fseeko() and ftello() and has no
application specific libraries:
% c89 -D_FILE_OFFSET_BITS=64 \
`getconf LFS_CFLAGS` a.c \
`getconf LFS_LDFLAGS` \
`getconf LFS_LIBS` \
Example 3: An example of compiling a program with a
"default" off_t and that uses fseeko() and ftello():
$ c89 -D_LARGEFILE_SOURCE a.c
SEE ALSO
csh(1), getconf(1), ksh(1), lint(1B), sh(1), fseek(3C),
ftell(3C), lf64(5), lfcompile64(5), standards(5)
NOTES
Certain system-specific or non-portable interfaces are not
usable in the large file compilation environment. Known
cases are:
o Kernel data structures read from /dev/kmem.
o Interfaces in the kernel virtual memory library,
-lkvm.
o Interfaces in the ELF access library, -lelf.
o Interfaces to /proc defined in <procfs.h>.
o The ustat(2) system call.
Programs that use these interfaces should not be compiled in
the large file compilation environment. As a partial safe-
guard against making this mistake, including either of the
<libelf.h> or <sys/procfs.h> header files will induce a com-
pilation error when the large file compilation environment
is enabled.
In general, caution should be exercised when using any
separately-compiled library whose interfaces include data
items of type off_t or the other redefined types either
directly or indirectly, such as with 'struct stat'. (The
redefined types are off_t, rlim_t, ino_t, blkcnt_t,
fsblkcnt_t, and fsfilcnt_t.) For the large file compilation
environment to work correctly with such a library, the
library interfaces must include the appropriate xxx64()
binary entry points and must have them mapped to the
corresponding primary functions when _FILE_OFFSET_BITS is
set to 64.
Care should be exercised using any of the printf() or
scanf() routines on variables of the types mentioned above.
In the large file compilation environment, these variables
should be printed or scanned using long long formats.
BUGS
The lint(1B) utility will generate spurious error messages
when _FILE_OFFSET_BITS is set to 64. This is because the
binary libc lint library, /usr/lib/llib-lc.ln, is compiled
only for the standard interfaces, not with _FILE_OFFSET_BITS
set to 64. This deficiency hampers static error-checking
for programs compiled in the large file compilation environ-
ment.
Symbolic formats analogous to those found in
<sys/int_fmtio.h> do not exist for printing or scanning
variables of the types that are redefined in the large file
compilation environment.
Man(1) output converted with
man2html