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CMake: Use -D_FILE_OFFSET_BITS=64 if (and only if) needed.

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A CMake option LARGE_FILE_SUPPORT is created if and only if
-D_FILE_OFFSET_BITS=64 affects sizeof(off_t).

This is needed on many 32-bit platforms and even with 64-bit builds
with MinGW-w64 to get support for files larger than 2 GiB.
This commit is contained in:
Lasse Collin 2023-09-27 00:58:17 +03:00
parent 1bc548b821
commit 597f49b614
2 changed files with 58 additions and 1 deletions
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7
CMakeLists.txt
View file

@ -9,7 +9,6 @@
#
# On some platforms this builds also xz and xzdec, but these are
# highly experimental and meant for testing only:
# - No large file support on those 32-bit platforms that need it
# - No translations
#
# Other missing things:
@ -51,6 +50,7 @@ include(CheckIncludeFile)
include(CheckSymbolExists)
include(CheckStructHasMember)
include(CheckCSourceCompiles)
include(cmake/tuklib_large_file_support.cmake)
include(cmake/tuklib_integer.cmake)
include(cmake/tuklib_cpucores.cmake)
include(cmake/tuklib_physmem.cmake)
@ -150,6 +150,11 @@ add_compile_definitions(
# it also adds the definitions to CMAKE_REQUIRED_DEFINITIONS.
tuklib_use_system_extensions(ALL)
# Check for large file support. It's required on some 32-bit platforms and
# even on 64-bit MinGW-w64 to get 64-bit off_t. This can be forced off on
# the CMake command line if needed: -DLARGE_FILE_SUPPORT=OFF
tuklib_large_file_support(ALL)
# This is needed by liblzma and xz.
tuklib_integer(ALL)

52
cmake/tuklib_large_file_support.cmake Normal file
View file

@ -0,0 +1,52 @@
#
# tuklib_large_file_support.cmake
#
# If off_t is less than 64 bits by default and -D_FILE_OFFSET_BITS=64
# makes off_t become 64-bit, the CMake option LARGE_FILE_SUPPORT is
# provided (ON by default) and -D_FILE_OFFSET_BITS=64 is added to
# the compile definitions if LARGE_FILE_SUPPORT is ON.
#
# Author: Lasse Collin
#
# This file has been put into the public domain.
# You can do whatever you want with this file.
#
include("${CMAKE_CURRENT_LIST_DIR}/tuklib_common.cmake")
include(CheckCSourceCompiles)
function(tuklib_large_file_support TARGET_OR_ALL)
# MSVC must be handled specially in the C code.
if(MSVC)
return()
endif()
set(TUKLIB_LARGE_FILE_SUPPORT_TEST
"#include <sys/types.h>
int foo[sizeof(off_t) >= 8 ? 1 : -1];
int main(void) { return 0; }")
check_c_source_compiles("${TUKLIB_LARGE_FILE_SUPPORT_TEST}"
TUKLIB_LARGE_FILE_SUPPORT_BY_DEFAULT)
if(NOT TUKLIB_LARGE_FILE_SUPPORT_BY_DEFAULT)
cmake_push_check_state()
# This needs -D.
list(APPEND CMAKE_REQUIRED_DEFINITIONS "-D_FILE_OFFSET_BITS=64")
check_c_source_compiles("${TUKLIB_LARGE_FILE_SUPPORT_TEST}"
TUKLIB_LARGE_FILE_SUPPORT_WITH_FOB64)
cmake_pop_check_state()
endif()
if(TUKLIB_LARGE_FILE_SUPPORT_WITH_FOB64)
# Show the option only when _FILE_OFFSET_BITS=64 affects sizeof(off_t).
option(LARGE_FILE_SUPPORT
"Use -D_FILE_OFFSET_BITS=64 to support files larger than 2 GiB."
ON)
if(LARGE_FILE_SUPPORT)
# This must not use -D.
tuklib_add_definitions("${TARGET_OR_ALL}" "_FILE_OFFSET_BITS=64")
endif()
endif()
endfunction()