The reference is resolved as branching to the next instruction.
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If the reference to a missing weak function is made from code that compiles to a branch or branch link instruction, then either: The _weak keyword can be applied to function and variable declarations, and to function definitions.įor declarations, this storage class specifies an extern object declaration that, even if not present, does not cause the linker to fault an unresolved reference. This keyword instructs the compiler to export symbols weakly. _svc(42) _value_in_regs res_type terminate_3(int procnum) _svc(42) int terminate_2(int procnum) // terminate_2 returns one result When an ARM architecture variant or ARM architecture-based processor that does not support an SVC instruction is specified on the command line using the -cpu option, the compiler generates an error.Įxample _svc(42) void terminate_1(int procnum) // terminate_1 returns no results
You can use the _value_in_regs qualifier 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. This causes function invocations to be compiled inline as an AAPCS-compliant operation that behaves similarly to a normal call to a function. It is an expression evaluating to an integer in the range:Ġ to 224–1 (a 24-bit value) in an ARM instruction.Ġ-255 (an 8-bit value) in a 16-bit Thumb instruction. Is the immediate value used in the SVC instruction. _svc(int svc_num) return-type function-name() 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. Return p->z + p->x // only unaligned read for z For example: int qadd(int i, int j) Y // 8 byte structure, natural alignment = 2 The _asm keyword can incorporate inline assembly into a function. _asm void my_strcpy(const char *src, char *dst) The _asm keyword can declare or define an embedded assembly function. The precise action of this keyword depends on its usage. This keyword passes information from the compiler to the ARM assembler armasm. 5.#pragma anon_unions, #pragma no_anon_unions.8._attribute_((used)) function attribute.7._attribute_((always_inline)) function attribute.6._attribute_((weak)) function attribute.5._attribute_((packed)) type attribute.4._attribute_((unused)) function attribute.3._attribute_((naked)) function attribute.2._attribute_((section("name"))) variable attribute.1._attribute_((aligned)) variable attribute.一、Compiler-specific Keywords and Operators.
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