RealView Compilation Tools Compiler Reference Guide - ARM ...

Compiler-specific Features
4.5.5 __attribute__((packed))
The packed variable attribute specifies that a variable or structure field has the smallest
possible alignment. That is, one byte for a variable, and one bit for a field, unless you
specify a larger value with the aligned attribute.
Note
This variable attribute is a GNU compiler extension that is supported by the ARM
compiler.
Example
struct
{
char a;
int b __attribute__ ((packed));
} Variable_Attributes_packed_0;
See also
• Packed structures on page 5-10
• The __packed qualifier and unaligned accesses to data on page 4-24 in the
Compiler User Guide
• __packed structures versus individually __packed fields on page 4-26 in the
Compiler User Guide.
4.5.6 __attribute__((section))
Normally, the ARM compiler places the objects it generates in sections like data and
bss. However, you might require additional data sections or you might want a variable
to appear in a special section, for example, to map to special hardware. The section
attribute specifies that a variable must be placed in a particular data section. If you use
the section attribute, read-only variables are placed in RO data sections, read-write
variables are placed in RW data sections unless you use the zero_init attribute. In this
case, the variable is placed in a ZI section.
Note
This variable attribute is a GNU compiler extension that is supported by the ARM
compiler.
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