The x86 assembler supports all instructions for the following processors, including the MMX extensions to the x86 architecture, and generates code only for a 32-bit flat memory space:

• 80486
• Pentium
• Pentium Pro processors

This chapter provides information specific to the x86 processor family.

This chapter includes the following topics:

Related Documentation COFF Support x86-Specific Assembler Settings

Related Documentation

Programming the 80386 (by Crawford & Gelsinger, Sybex), is helpful for writing x86 assembly language code. The book includes extra instructions introduced for later processors.

COFF Support

In addition to supporting the ELF (Executable and Linkable Format) object file format, the x86 assembler supports COFF (Common Object File Format).

NOTE

For information on using the .section directive with ELF, see "section".

If you are generating COFF format, the .section directive has the following syntax:

  .section name [,flags]

Defines a section in an object file.

Table 6.1 describes the syntax elements for the COFF .section directive.

Syntax descriptions for COFF .section directive:

Syntax Element	Description
name	The name of the section.
flags	Numeric value that indicates the COFF section flags. You must specify the flags as the bitwise OR of the applicable values in Table 6.2.

Table 6.2 shows the COFF section flags that you can specify.

NOTE

To use symbolic names for the flags, you must define each name as an equate.

Flag	Name	Description
0x00000000	IMAGE_SCN_TYPE_REG	Reserved for future use.
0x00000001	IMAGE_SCN_TYPE_DSECT	Reserved for future use.
0x00000002	IMAGE_SCN_TYPE_NOLOAD	Reserved for future use.
0x00000004	IMAGE_SCN_TYPE_GROUP	Reserved for future use.
0x00000008	IMAGE_SCN_TYPE_NO_PAD	Indicates that the section should not be padded to the next boundary.
0x00000010	IMAGE_SCN_TYPE_COPY	Reserved for future use.
0x00000020	IMAGE_SCN_CNT_CODE	Indicates that the section contains executable code.
0x00000040	IMAGE_SCN_CNT_INITIALIZED _DATA	Indicates that the section contains initialized data.
0x00000080	IMAGE_SCN_CNT_UNINITIALIZED _DATA	Indicates that the section contains uninitialized data.
0x00000100	IMAGE_SCN_LNK_OTHER	Reserved for future use.
0x00000200	IMAGE_SCN_LNK_INFO	Indicates that the section contains comments or other information.
0x00000400	IMAGE_SCN_TYPE_OVER	Reserved for future use.
0x00000800	IMAGE_SCN_LNK_REMOVE	Indicates that the section will not be part of the executable image.
0x00001000	IMAGE_SCN_LNK_COMDAT	Indicates that the section contains COMDAT data.
0x00008000	IMAGE_SCN_MEM_FARDATA	Reserved for future use.
0x00020000	IMAGE_SCN_MEM_PURGEABLE	Reserved for future use.
0x00020000	IMAGE_SCN_MEM_16BIT	Reserved for future use.
0x00040000	IMAGE_SCN_MEM_LOCKED	Reserved for future use.
0x00080000	IMAGE_SCN_MEM_PRELOAD	Reserved for future use.
0x00100000	IMAGE_SCN_ALIGN_1BYTES	Indicates that the section must be aligned on a 1-byte boundary.
0x00200000	IMAGE_SCN_ALIGN_2BYTES	Indicates that the section must be aligned on a 2-byte boundary.
0x00300000	IMAGE_SCN_ALIGN_4BYTES	Indicates that the section must be aligned on a 4-byte boundary.
0x00400000	IMAGE_SCN_ALIGN_8BYTES	Indicates that the section must be aligned on an 8-byte boundary.
0x00500000	IMAGE_SCN_ALIGN_16BYTES	Indicates that the section must be aligned on a 16-byte boundary.
0x00600000	IMAGE_SCN_ALIGN_32BYTES	Indicates that the section must be aligned on a 32-byte boundary.
0x00700000	IMAGE_SCN_ALIGN_64BYTES	Indicates that the section must be aligned on a 64-byte boundary.
0x00800000	IMAGE_SCN_ALIGN_128BYTES	Indicates that the section must be aligned on a 128-byte boundary.
0x00900000	IMAGE_SCN_ALIGN_256BYTES	Indicates that the section must be aligned on a 256-byte boundary.
0x00A00000	IMAGE_SCN_ALIGN_512BYTES	Indicates that the section must be aligned on a 512-byte boundary.
0x00B00000	IMAGE_SCN_ALIGN_1024BYTES	Indicates that the section must be aligned on a 1024-byte boundary.
0x00C00000	IMAGE_SCN_ALIGN_2048BYTES	Indicates that the section must be aligned on a 2048-byte boundary.
0x00D00000	IMAGE_SCN_ALIGN_4096BYTES	Indicates that the section must be aligned on a 4096-byte boundary.
0x00E00000	IMAGE_SCN_ALIGN_8192BYTES	Indicates that the section must be aligned on an 8192-byte boundary.
0x01000000	IMAGE_SCN_LNK_NRELOC_OVFL	Indicates that the section contains extended relocations.
0x02000000	IMAGE_SCN_MEM_DISCARDABLE	Indicates that the section can be discarded.
0x04000000	IMAGE_SCN_MEM_NOT_CACHED	Indicates that the section cannot be cached.
0x08000000	IMAGE_SCN_MEM_NOT_PAGED	Indicates that the section cannot be paged.
0x10000000	IMAGE_SCN_MEM_SHARED	Indicates that the section can be shared in memory.
0x20000000	IMAGE_SCN_MEM_EXECUTE	Indicates that the section can be executed as code.
0x40000000	IMAGE_SCN_MEM_READ	Indicates that the section is readable.
0x80000000	IMAGE_SCN_MEM_WRITE	Indicates that the section is writable.

Listing 6.1 shows definitions of text, data, and zero-initialized data sections.

COFF example section definitions:

; .text -- a section containing executable code
section .text, 0x6000102
; IMAGE_SCN_MEM_READ | IMAGE_SCN_MEM_EXECUTE |
; IMAGE_SCN_LNK_COMDAT | IMAGE_SCN_CNT_CODE
; .data -- a section containing initialized data
section .data, 0xC0301040
;  IMAGE_SCN_MEM_READ | IMAGE_SCN_MEM_WRITE |
;  IMAGE_SCN_ALIGN_4BYTES | IMAGE_SCN_LNK_COMDAT |
;  IMAGE_SCN_CNT_INITIALIZED_DATA
; .bss -- a section containing zero-intialized data
section .bss, 0xC0301080
;  IMAGE_SCN_MEM_READ | IMAGE_SCN_MEM_WRITE |
;  IMAGE_SCN_ALIGN_4BYTES | IMAGE_SCN_LNK_COMDAT |
;  IMAGE_SCN_CNT_UNINITIALIZED_DATA

x86-Specific Assembler Settings

This section documents the settings on the Assembler target settings panel that are specific to the x86 assembler. Figure 6.1 shows the Assembler target settings panel for the x86 assembler.

Assembler target settings panel for x86 assembler:

You can use the x86 assembler to generate code for several different instruction sets that are available for x86 processors. The Instructions Sets group of the Assembler target settings panel includes the following checkboxes, which you can select to indicate the instruction sets you want to use:

• 80386
• 80387
• 80486
• Pentium
• MMX
• K6 / 3D-Now!

NOTE

For information on the other settings shown in Figure 6.1, see "Common Assembler Settings".