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comparison doc/manual/callconvs/callconv_arm64.tex @ 499:fc614cb865c6

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- doc and disasexample additions specific to non-trivial C++ aggregates as return values (incl. fixes to doc and additional LSB specific PPC32 section)
author Tassilo Philipp
date Mon, 04 Apr 2022 15:50:52 +0200
parents 0fc22b5feac7
children
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498:fd9ba3a6d348 499:fc614cb865c6
77 \item subsequent parameters are pushed onto the stack 77 \item subsequent parameters are pushed onto the stack
78 \item if the callee takes the address of one of the parameters and uses it to address other parameters (e.g. varargs) it has to copy - in its prolog - the first 8 integer 78 \item if the callee takes the address of one of the parameters and uses it to address other parameters (e.g. varargs) it has to copy - in its prolog - the first 8 integer
79 and 8 floating-point registers to a reserved stack area adjacent to the other parameters on the stack (only the unnamed integer parameters require saving, though) 79 and 8 floating-point registers to a reserved stack area adjacent to the other parameters on the stack (only the unnamed integer parameters require saving, though)
80 \item aggregates (struct, union) with 1 to 4 identical floating-point members (either float or double) are passed field-by-field (8-byte aligned if passed via stack), except if passed as a vararg 80 \item aggregates (struct, union) with 1 to 4 identical floating-point members (either float or double) are passed field-by-field (8-byte aligned if passed via stack), except if passed as a vararg
81 \item other aggregates (struct, union) \textgreater\ 16 bytes in size are passed indirectly, as a pointer to a copy (if needed) 81 \item other aggregates (struct, union) \textgreater\ 16 bytes in size are passed indirectly, as a pointer to a copy (if needed)
82 \item {\it non-trivial} C++ aggregates (as defined by the language) of any size, are passed indirectly via a pointer to a copy of the aggregate
82 \item all other aggregates (struct, union), after rounding up the size to the nearest multiple of 8, are passed as a sequence of dwords, like integers 83 \item all other aggregates (struct, union), after rounding up the size to the nearest multiple of 8, are passed as a sequence of dwords, like integers
83 \item aggregates are never split across registers and stack, so if not enough registers are available an aggregated is passed via the stack (for aggregates that 84 \item aggregates are never split across registers and stack, so if not enough registers are available an aggregated is passed via the stack (for aggregates that
84 would've been passed as floating point values, any still unused float registers will be skipped for any subsequent arg) 85 would've been passed as floating point values, any still unused float registers will be skipped for any subsequent arg)
85 \item stack is required throughout to be eight-byte aligned 86 \item stack is required throughout to be eight-byte aligned
86 \end{itemize} 87 \end{itemize}
88 \paragraph{Return values} 89 \paragraph{Return values}
89 90
90 \begin{itemize} 91 \begin{itemize}
91 \item integer return values use x0 92 \item integer return values use x0
92 \item floating-point return values use d0 93 \item floating-point return values use d0
94 \item for {\it non-trivial} C++ aggregates, the caller allocates space, passes pointer to it to the callee via x8, and callee writes return value to this space; the ptr to the aggregate is returned in x0
93 \item aggregates (struct, union) that would be passed via registers if passed as a first param, are returned via those registers 95 \item aggregates (struct, union) that would be passed via registers if passed as a first param, are returned via those registers
94 \item for aggregates not returnable via registers (e.g. if regs exhausted, or \textgreater\ 16b, ...), the caller allocates space, passes pointer to it to the callee through 96 \item for aggregates not returnable via registers (e.g. if regs exhausted, or \textgreater\ 16b, ...), the caller allocates space, passes pointer to it to the callee through
95 x8, and callee writes return value to this space (note that this is not a hidden first param, as x8 is not used for passing params); the ptr to the aggregate is returned in x0 97 x8, and callee writes return value to this space (note that this is not a hidden first param, as x8 is not used for passing params); the ptr to the aggregate is returned in x0
96 \end{itemize} 98 \end{itemize}
97 99