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| author | alk3pInjection <webmaster@raspii.tech> | 2024-02-04 16:16:35 +0800 |
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| committer | alk3pInjection <webmaster@raspii.tech> | 2024-02-04 16:16:35 +0800 |
| commit | abdaadbcae30fe0c9a66c7516798279fdfd97750 (patch) | |
| tree | 00a54a6e25601e43876d03c1a4a12a749d4a914c /share/doc/gccint/Varargs.html | |
https://developer.arm.com/downloads/-/arm-gnu-toolchain-downloads
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diff --git a/share/doc/gccint/Varargs.html b/share/doc/gccint/Varargs.html new file mode 100644 index 0000000..da016d5 --- /dev/null +++ b/share/doc/gccint/Varargs.html @@ -0,0 +1,252 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- Copyright (C) 1988-2023 Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with the +Invariant Sections being "Funding Free Software", the Front-Cover +Texts being (a) (see below), and with the Back-Cover Texts being (b) +(see below). A copy of the license is included in the section entitled +"GNU Free Documentation License". + +(a) The FSF's Front-Cover Text is: + +A GNU Manual + +(b) The FSF's Back-Cover Text is: + +You have freedom to copy and modify this GNU Manual, like GNU + software. Copies published by the Free Software Foundation raise + funds for GNU development. --> +<!-- Created by GNU Texinfo 5.1, http://www.gnu.org/software/texinfo/ --> +<head> +<title>GNU Compiler Collection (GCC) Internals: Varargs</title> + +<meta name="description" content="GNU Compiler Collection (GCC) Internals: Varargs"> +<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Varargs"> +<meta name="resource-type" content="document"> +<meta name="distribution" content="global"> +<meta name="Generator" content="makeinfo"> +<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> +<link href="index.html#Top" rel="start" title="Top"> +<link href="Option-Index.html#Option-Index" rel="index" title="Option Index"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="Target-Macros.html#Target-Macros" rel="up" title="Target Macros"> +<link href="Trampolines.html#Trampolines" rel="next" title="Trampolines"> +<link href="Miscellaneous-Register-Hooks.html#Miscellaneous-Register-Hooks" rel="previous" title="Miscellaneous Register Hooks"> +<style type="text/css"> +<!-- +a.summary-letter {text-decoration: none} +blockquote.smallquotation {font-size: smaller} +div.display {margin-left: 3.2em} +div.example {margin-left: 3.2em} +div.indentedblock {margin-left: 3.2em} +div.lisp {margin-left: 3.2em} +div.smalldisplay {margin-left: 3.2em} +div.smallexample {margin-left: 3.2em} +div.smallindentedblock {margin-left: 3.2em; font-size: smaller} +div.smalllisp {margin-left: 3.2em} +kbd {font-style:oblique} +pre.display {font-family: inherit} +pre.format {font-family: inherit} +pre.menu-comment {font-family: serif} +pre.menu-preformatted {font-family: serif} +pre.smalldisplay {font-family: inherit; font-size: smaller} +pre.smallexample {font-size: smaller} +pre.smallformat {font-family: inherit; font-size: smaller} +pre.smalllisp {font-size: smaller} +span.nocodebreak {white-space:nowrap} +span.nolinebreak {white-space:nowrap} +span.roman {font-family:serif; font-weight:normal} +span.sansserif {font-family:sans-serif; font-weight:normal} +ul.no-bullet {list-style: none} +--> +</style> + + +</head> + +<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> +<a name="Varargs"></a> +<div class="header"> +<p> +Next: <a href="Trampolines.html#Trampolines" accesskey="n" rel="next">Trampolines</a>, Previous: <a href="Stack-and-Calling.html#Stack-and-Calling" accesskey="p" rel="previous">Stack and Calling</a>, Up: <a href="Target-Macros.html#Target-Macros" accesskey="u" rel="up">Target Macros</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p> +</div> +<hr> +<a name="Implementing-the-Varargs-Macros"></a> +<h3 class="section">18.10 Implementing the Varargs Macros</h3> +<a name="index-varargs-implementation"></a> + +<p>GCC comes with an implementation of <code><varargs.h></code> and +<code><stdarg.h></code> that work without change on machines that pass arguments +on the stack. Other machines require their own implementations of +varargs, and the two machine independent header files must have +conditionals to include it. +</p> +<p>ISO <code><stdarg.h></code> differs from traditional <code><varargs.h></code> mainly in +the calling convention for <code>va_start</code>. The traditional +implementation takes just one argument, which is the variable in which +to store the argument pointer. The ISO implementation of +<code>va_start</code> takes an additional second argument. The user is +supposed to write the last named argument of the function here. +</p> +<p>However, <code>va_start</code> should not use this argument. The way to find +the end of the named arguments is with the built-in functions described +below. +</p> +<dl> +<dt><a name="index-_005f_005fbuiltin_005fsaveregs"></a>Macro: <strong>__builtin_saveregs</strong> <em>()</em></dt> +<dd><p>Use this built-in function to save the argument registers in memory so +that the varargs mechanism can access them. Both ISO and traditional +versions of <code>va_start</code> must use <code>__builtin_saveregs</code>, unless +you use <code>TARGET_SETUP_INCOMING_VARARGS</code> (see below) instead. +</p> +<p>On some machines, <code>__builtin_saveregs</code> is open-coded under the +control of the target hook <code>TARGET_EXPAND_BUILTIN_SAVEREGS</code>. On +other machines, it calls a routine written in assembler language, +found in <samp>libgcc2.c</samp>. +</p> +<p>Code generated for the call to <code>__builtin_saveregs</code> appears at the +beginning of the function, as opposed to where the call to +<code>__builtin_saveregs</code> is written, regardless of what the code is. +This is because the registers must be saved before the function starts +to use them for its own purposes. +</p></dd></dl> + +<dl> +<dt><a name="index-_005f_005fbuiltin_005fnext_005farg"></a>Macro: <strong>__builtin_next_arg</strong> <em>(<var>lastarg</var>)</em></dt> +<dd><p>This builtin returns the address of the first anonymous stack +argument, as type <code>void *</code>. If <code>ARGS_GROW_DOWNWARD</code>, it +returns the address of the location above the first anonymous stack +argument. Use it in <code>va_start</code> to initialize the pointer for +fetching arguments from the stack. Also use it in <code>va_start</code> to +verify that the second parameter <var>lastarg</var> is the last named argument +of the current function. +</p></dd></dl> + +<dl> +<dt><a name="index-_005f_005fbuiltin_005fclassify_005ftype"></a>Macro: <strong>__builtin_classify_type</strong> <em>(<var>object</var>)</em></dt> +<dd><p>Since each machine has its own conventions for which data types are +passed in which kind of register, your implementation of <code>va_arg</code> +has to embody these conventions. The easiest way to categorize the +specified data type is to use <code>__builtin_classify_type</code> together +with <code>sizeof</code> and <code>__alignof__</code>. +</p> +<p><code>__builtin_classify_type</code> ignores the value of <var>object</var>, +considering only its data type. It returns an integer describing what +kind of type that is—integer, floating, pointer, structure, and so on. +</p> +<p>The file <samp>typeclass.h</samp> defines an enumeration that you can use to +interpret the values of <code>__builtin_classify_type</code>. +</p></dd></dl> + +<p>These machine description macros help implement varargs: +</p> +<dl> +<dt><a name="index-TARGET_005fEXPAND_005fBUILTIN_005fSAVEREGS"></a>Target Hook: <em>rtx</em> <strong>TARGET_EXPAND_BUILTIN_SAVEREGS</strong> <em>(void)</em></dt> +<dd><p>If defined, this hook produces the machine-specific code for a call to +<code>__builtin_saveregs</code>. This code will be moved to the very +beginning of the function, before any parameter access are made. The +return value of this function should be an RTX that contains the value +to use as the return of <code>__builtin_saveregs</code>. +</p></dd></dl> + +<dl> +<dt><a name="index-TARGET_005fSETUP_005fINCOMING_005fVARARGS"></a>Target Hook: <em>void</em> <strong>TARGET_SETUP_INCOMING_VARARGS</strong> <em>(cumulative_args_t <var>args_so_far</var>, const function_arg_info <var>&arg</var>, int *<var>pretend_args_size</var>, int <var>second_time</var>)</em></dt> +<dd><p>This target hook offers an alternative to using +<code>__builtin_saveregs</code> and defining the hook +<code>TARGET_EXPAND_BUILTIN_SAVEREGS</code>. Use it to store the anonymous +register arguments into the stack so that all the arguments appear to +have been passed consecutively on the stack. Once this is done, you can +use the standard implementation of varargs that works for machines that +pass all their arguments on the stack. +</p> +<p>The argument <var>args_so_far</var> points to the <code>CUMULATIVE_ARGS</code> data +structure, containing the values that are obtained after processing the +named arguments. The argument <var>arg</var> describes the last of these named +arguments. The argument <var>arg</var> should not be used if the function type +satisfies <code>TYPE_NO_NAMED_ARGS_STDARG_P</code>, since in that case there are +no named arguments and all arguments are accessed with <code>va_arg</code>. +</p> +<p>The target hook should do two things: first, push onto the stack all the +argument registers <em>not</em> used for the named arguments, and second, +store the size of the data thus pushed into the <code>int</code>-valued +variable pointed to by <var>pretend_args_size</var>. The value that you +store here will serve as additional offset for setting up the stack +frame. +</p> +<p>Because you must generate code to push the anonymous arguments at +compile time without knowing their data types, +<code>TARGET_SETUP_INCOMING_VARARGS</code> is only useful on machines that +have just a single category of argument register and use it uniformly +for all data types. +</p> +<p>If the argument <var>second_time</var> is nonzero, it means that the +arguments of the function are being analyzed for the second time. This +happens for an inline function, which is not actually compiled until the +end of the source file. The hook <code>TARGET_SETUP_INCOMING_VARARGS</code> should +not generate any instructions in this case. +</p></dd></dl> + +<dl> +<dt><a name="index-TARGET_005fSTRICT_005fARGUMENT_005fNAMING"></a>Target Hook: <em>bool</em> <strong>TARGET_STRICT_ARGUMENT_NAMING</strong> <em>(cumulative_args_t <var>ca</var>)</em></dt> +<dd><p>Define this hook to return <code>true</code> if the location where a function +argument is passed depends on whether or not it is a named argument. +</p> +<p>This hook controls how the <var>named</var> argument to <code>TARGET_FUNCTION_ARG</code> +is set for varargs and stdarg functions. If this hook returns +<code>true</code>, the <var>named</var> argument is always true for named +arguments, and false for unnamed arguments. If it returns <code>false</code>, +but <code>TARGET_PRETEND_OUTGOING_VARARGS_NAMED</code> returns <code>true</code>, +then all arguments are treated as named. Otherwise, all named arguments +except the last are treated as named. +</p> +<p>You need not define this hook if it always returns <code>false</code>. +</p></dd></dl> + +<dl> +<dt><a name="index-TARGET_005fCALL_005fARGS"></a>Target Hook: <em>void</em> <strong>TARGET_CALL_ARGS</strong> <em>(rtx, <var>tree</var>)</em></dt> +<dd><p>While generating RTL for a function call, this target hook is invoked once +for each argument passed to the function, either a register returned by +<code>TARGET_FUNCTION_ARG</code> or a memory location. It is called just +before the point where argument registers are stored. The type of the +function to be called is also passed as the second argument; it is +<code>NULL_TREE</code> for libcalls. The <code>TARGET_END_CALL_ARGS</code> hook is +invoked just after the code to copy the return reg has been emitted. +This functionality can be used to perform special setup of call argument +registers if a target needs it. +For functions without arguments, the hook is called once with <code>pc_rtx</code> +passed instead of an argument register. +Most ports do not need to implement anything for this hook. +</p></dd></dl> + +<dl> +<dt><a name="index-TARGET_005fEND_005fCALL_005fARGS"></a>Target Hook: <em>void</em> <strong>TARGET_END_CALL_ARGS</strong> <em>(void)</em></dt> +<dd><p>This target hook is invoked while generating RTL for a function call, +just after the point where the return reg is copied into a pseudo. It +signals that all the call argument and return registers for the just +emitted call are now no longer in use. +Most ports do not need to implement anything for this hook. +</p></dd></dl> + +<dl> +<dt><a name="index-TARGET_005fPRETEND_005fOUTGOING_005fVARARGS_005fNAMED"></a>Target Hook: <em>bool</em> <strong>TARGET_PRETEND_OUTGOING_VARARGS_NAMED</strong> <em>(cumulative_args_t <var>ca</var>)</em></dt> +<dd><p>If you need to conditionally change ABIs so that one works with +<code>TARGET_SETUP_INCOMING_VARARGS</code>, but the other works like neither +<code>TARGET_SETUP_INCOMING_VARARGS</code> nor <code>TARGET_STRICT_ARGUMENT_NAMING</code> was +defined, then define this hook to return <code>true</code> if +<code>TARGET_SETUP_INCOMING_VARARGS</code> is used, <code>false</code> otherwise. +Otherwise, you should not define this hook. +</p></dd></dl> + +<hr> +<div class="header"> +<p> +Next: <a href="Trampolines.html#Trampolines" accesskey="n" rel="next">Trampolines</a>, Previous: <a href="Stack-and-Calling.html#Stack-and-Calling" accesskey="p" rel="previous">Stack and Calling</a>, Up: <a href="Target-Macros.html#Target-Macros" accesskey="u" rel="up">Target Macros</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p> +</div> + + + +</body> +</html> |