RealView Compilation Tools Compiler Reference Guide - ARM ...

Compiler-specific Features
Note
In C++, if a virtual function qualified with the __softfp keyword is to be overridden, the
overriding function must also be declared as __softfp. If the functions do not match, the
compiler generates an error.
See also
• --fpu=name on page 2-42
• #pragma [no_]softfp_linkage on page 4-59
• Floating-point linkage on page 4-33 in the Compiler User Guide.
4.1.15 __svc
The __svc keyword declares a SuperVisor Call (SVC) function taking up to four
integer-like arguments and returning up to four results in a value_in_regs structure.
__svc is a function qualifier. It affects the type of a function.
Syntax
__svc(int svc_num) return-type function-name([argument-list]);
Where:
svc_num
Is the immediate value used in the SVC instruction.
It is an expression evaluating to an integer in the range:
• 0 to 2 24 –1 (a 24-bit value) in an ARM instruction
• 0-255 (an 8-bit value) in a 16-bit Thumb instruction.
Usage
This causes function invocations to be compiled inline as an AAPCS-compliant
operation that behaves similarly to a normal call to a function.
The __value_in_regs qualifier can be used to specify that a small structure of up to 16
bytes is returned in registers, rather than by the usual structure-passing mechanism
defined in the AAPCS.
Example
__svc(42) void terminate_1(int procnum); // terminate_1 returns no results
__svc(42) int terminate_2(int procnum); // terminate_2 returns one result
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