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comparison doc/manual/callconvs/callconv_ppc32.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 6c72cb768099
children 585dcb68f55d
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498:fd9ba3a6d348 499:fc614cb865c6
94 \item composite parameters with size of 1 or 2 bytes occupy low-order bytes of their 4-byte area. INCONSISTENT with other 32-bit PPC 94 \item composite parameters with size of 1 or 2 bytes occupy low-order bytes of their 4-byte area. INCONSISTENT with other 32-bit PPC
95 binary interfaces. In AIX and mac OS 9, padding bytes always follow the data structure 95 binary interfaces. In AIX and mac OS 9, padding bytes always follow the data structure
96 \item composite parameters 3 bytes or larger in size occupy high-order bytes 96 \item composite parameters 3 bytes or larger in size occupy high-order bytes
97 \item integer parameters \textless\ 32 bit are right-justified (meaning occupy higher-address bytes) in their 4-byte slot on the stack, requiring extra-care for big-endian targets 97 \item integer parameters \textless\ 32 bit are right-justified (meaning occupy higher-address bytes) in their 4-byte slot on the stack, requiring extra-care for big-endian targets
98 \item aggregates (struct, union) with only one (non-aggregate / non-array) field are passed as if the field itself would be passed 98 \item aggregates (struct, union) with only one (non-aggregate / non-array) field are passed as if the field itself would be passed
99 \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
99 \item all other aggregates are passed as a sequence of words (like integer parameters) 100 \item all other aggregates are passed as a sequence of words (like integer parameters)
100 \end{itemize} 101 \end{itemize}
101 102
102 103
103 \paragraph{Return values} 104 \paragraph{Return values}
104 105
105 \begin{itemize} 106 \begin{itemize}
106 \item return values of integer \textless=\ 32bit or pointer type use gpr3 107 \item return values of integer \textless=\ 32bit or pointer type use gpr3
107 \item 64 bit integers use gpr3 and gpr4 (hiword in gpr3, loword in gpr4) 108 \item 64 bit integers use gpr3 and gpr4 (hiword in gpr3, loword in gpr4)
108 \item floating point values are returned via fpr1 109 \item floating point values are returned via fpr1
109 \item aggregates (struct, union) \textless=\ 64 bits use gpr3 and gpr4 110 \item for all aggregates, the caller allocates space, passes pointer to it to the callee as a hidden first param
110 \item for all other aggregates and types \textgreater\ 64 bits, a secret first parameter with an address to a caller allocated space is passed to the function (in gpr3), which is written to by the callee 111 (meaning in gpr3), and callee writes return value to this space; the ptr to the aggregate is returned in gpr3
111 \end{itemize} 112 \end{itemize}
112 113
113 114
114 \paragraph{Stack layout} 115 \paragraph{Stack layout}
115 116
207 or passed on the stack; they are never splitted into a register and stack part 208 or passed on the stack; they are never splitted into a register and stack part
208 \item Ellipsis calls set CR bit 6 209 \item Ellipsis calls set CR bit 6
209 \item integer parameters \textless\ 32 bit are right-justified (meaning occupy high-order bytes) in their 4-byte area, requiring extra-care for big-endian targets 210 \item integer parameters \textless\ 32 bit are right-justified (meaning occupy high-order bytes) in their 4-byte area, requiring extra-care for big-endian targets
210 \item no spill area is used on stack, iterating over varargs requires a specific va\_list implementation 211 \item no spill area is used on stack, iterating over varargs requires a specific va\_list implementation
211 \item aggregates (struct, union) and types \textgreater\ 64 bits are passed indirectly, as a pointer to the data (or a copy of it, if necessary to avoid modification) 212 \item aggregates (struct, union) and types \textgreater\ 64 bits are passed indirectly, as a pointer to the data (or a copy of it, if necessary to avoid modification)
213 \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
212 \end{itemize} 214 \end{itemize}
213 215
214 \paragraph{Return values} 216 \paragraph{Return values}
215 217
216 \begin{itemize} 218 \begin{itemize}
217 \item 32-bit integers use register r3, 64-bit use registers r3 and r4 (hiword in r3, loword in r4) 219 \item 32-bit integers use register r3, 64-bit use registers r3 and r4 (hiword in r3, loword in r4)
218 \item floating-point values are returned using register f1 220 \item floating-point values are returned using register f1
221 \item for {\it non-trivial} C++ aggregates, the caller allocates space, passes pointer to it to the callee as a hidden first param
222 (meaning in gpr3), and callee writes return value to this space; the ptr to the aggregate is returned in gpr3
219 \item aggregates (struct, union) \textless=\ 64 bits use gpr3 and gpr4 223 \item aggregates (struct, union) \textless=\ 64 bits use gpr3 and gpr4
220 \item for all other aggregates and types \textgreater\ 64 bits, a secret first parameter with an address to a caller allocated space is passed to the function (in gpr3), which is written to by the callee 224 \item for all other aggregates and types \textgreater\ 64 bits, a secret first parameter with an address to a caller allocated space is passed to the function (in gpr3), which is written to by the callee
221 \end{itemize} 225 \end{itemize}
222 226
223 227
250 \hhline{~-~~} 254 \hhline{~-~~}
251 & \vdots & & \\ 255 & \vdots & & \\
252 \end{tabular} 256 \end{tabular}
253 \caption{Stack layout on System V ABI for PowerPC 32-bit calling convention} 257 \caption{Stack layout on System V ABI for PowerPC 32-bit calling convention}
254 \end{figure} 258 \end{figure}
259
260
261 \subsubsection{System V PPC 32-bit / Linux Standard Base version}
262
263 This is in essence the same as the System V PPC 32-bit calling convention, but differs for aggregate return values:
264 % @@@STRUCT make this more obvious
265
266 \begin{itemize}
267 \item for all aggregates, the caller allocates space, passes pointer to it to the callee as a hidden first param
268 (meaning in gpr3), and callee writes return value to this space; the ptr to the aggregate is returned in gpr3
269 \end{itemize}
255 270
256 271
257 \clearpage 272 \clearpage
258 273
259 \subsubsection{System V syscalls} 274 \subsubsection{System V syscalls}