Apple Darwin Manuel d'utilisateur télécharger pdf (Page 12)

There are many differences between 32-bit and 64-bit environments in OS X, including tool usage changes,

changes to the size and alignment of data types, alignment pragmas, and I/O Kit drivers. This chapter describes

the main changes developers should be aware of when porting code to 64-bit. You should read this chapter

if you've decided to port your code to 64-bit or if you are writing a new code from scratch.

Tools Changes

You'll find a number of issues when porting code to a 64-bit executable. You can address most of these issues

with subtle tweaks to your code. However, before you touch the first line of code, there are a few broad issues

you should be aware of:

●

Compiling an application as a 64-bit executable requires you to use GCC 4.0 or later. See Compiling 64-Bit

Code Using GCC (page 31) for information about related compiler flags.

●

Xcode has additional options related to 64-bit compilation. For information about compiling 64-bit

applications with Xcode, see Compiling 64-Bit Code Using Xcode (page 32).

●

Any tools that understand the Mach-O ABI (stack frames, calling convention, and so on) must change.

These changes affect mainly third-party compilers and linkers. For more information, see OS X ABI Mach-O

File Format Reference.

Data Type Changes

This section describes the changes to data type sizes and alignment in 64-bit executables, and explains how

these changes will impact your code.

Data Type Size and Alignment

OS X uses two data models: ILP32 (in which integers, long integers, and pointers are 32-bit quantities) and

LP64 (in which integers are 32-bit quantities, and long integers and pointers are 64-bit quantities). Other types

are equivalent to their 32-bit counterparts (except for size_t and a few others that are defined based on the

size of long integers or pointers).

Major 64-Bit Changes

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Apple Darwin Manuel d'utilisateur Page 12