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198 lines
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HTML
198 lines
10 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Copyright (C) 1988-2018 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being "Funding Free Software", the Front-Cover
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Texts being (a) (see below), and with the Back-Cover Texts being (b)
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(see below). A copy of the license is included in the section entitled
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"GNU Free Documentation License".
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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software. Copies published by the Free Software Foundation raise
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funds for GNU development. -->
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Stack Checking (GNU Compiler Collection (GCC) Internals)</title>
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<meta name="description" content="Stack Checking (GNU Compiler Collection (GCC) Internals)">
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<meta name="keywords" content="Stack Checking (GNU Compiler Collection (GCC) Internals)">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Stack-and-Calling.html#Stack-and-Calling" rel="up" title="Stack and Calling">
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<link href="Frame-Registers.html#Frame-Registers" rel="next" title="Frame Registers">
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<link href="Exception-Handling.html#Exception-Handling" rel="prev" title="Exception Handling">
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</style>
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</head>
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<body lang="en">
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<a name="Stack-Checking"></a>
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<div class="header">
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<p>
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Next: <a href="Frame-Registers.html#Frame-Registers" accesskey="n" rel="next">Frame Registers</a>, Previous: <a href="Exception-Handling.html#Exception-Handling" accesskey="p" rel="prev">Exception Handling</a>, Up: <a href="Stack-and-Calling.html#Stack-and-Calling" accesskey="u" rel="up">Stack and Calling</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>
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</div>
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<hr>
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<a name="Specifying-How-Stack-Checking-is-Done"></a>
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<h4 class="subsection">18.9.3 Specifying How Stack Checking is Done</h4>
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<p>GCC will check that stack references are within the boundaries of the
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stack, if the option <samp>-fstack-check</samp> is specified, in one of
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three ways:
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</p>
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<ol>
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<li> If the value of the <code>STACK_CHECK_BUILTIN</code> macro is nonzero, GCC
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will assume that you have arranged for full stack checking to be done
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at appropriate places in the configuration files. GCC will not do
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other special processing.
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</li><li> If <code>STACK_CHECK_BUILTIN</code> is zero and the value of the
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<code>STACK_CHECK_STATIC_BUILTIN</code> macro is nonzero, GCC will assume
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that you have arranged for static stack checking (checking of the
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static stack frame of functions) to be done at appropriate places
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in the configuration files. GCC will only emit code to do dynamic
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stack checking (checking on dynamic stack allocations) using the third
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approach below.
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</li><li> If neither of the above are true, GCC will generate code to periodically
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“probe” the stack pointer using the values of the macros defined below.
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</li></ol>
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<p>If neither STACK_CHECK_BUILTIN nor STACK_CHECK_STATIC_BUILTIN is defined,
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GCC will change its allocation strategy for large objects if the option
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<samp>-fstack-check</samp> is specified: they will always be allocated
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dynamically if their size exceeds <code>STACK_CHECK_MAX_VAR_SIZE</code> bytes.
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</p>
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<dl>
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<dt><a name="index-STACK_005fCHECK_005fBUILTIN"></a>Macro: <strong>STACK_CHECK_BUILTIN</strong></dt>
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<dd><p>A nonzero value if stack checking is done by the configuration files in a
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machine-dependent manner. You should define this macro if stack checking
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is required by the ABI of your machine or if you would like to do stack
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checking in some more efficient way than the generic approach. The default
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value of this macro is zero.
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</p></dd></dl>
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<dl>
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<dt><a name="index-STACK_005fCHECK_005fSTATIC_005fBUILTIN"></a>Macro: <strong>STACK_CHECK_STATIC_BUILTIN</strong></dt>
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<dd><p>A nonzero value if static stack checking is done by the configuration files
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in a machine-dependent manner. You should define this macro if you would
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like to do static stack checking in some more efficient way than the generic
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approach. The default value of this macro is zero.
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</p></dd></dl>
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<dl>
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<dt><a name="index-STACK_005fCHECK_005fPROBE_005fINTERVAL_005fEXP"></a>Macro: <strong>STACK_CHECK_PROBE_INTERVAL_EXP</strong></dt>
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<dd><p>An integer specifying the interval at which GCC must generate stack probe
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instructions, defined as 2 raised to this integer. You will normally
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define this macro so that the interval be no larger than the size of
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the “guard pages” at the end of a stack area. The default value
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of 12 (4096-byte interval) is suitable for most systems.
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</p></dd></dl>
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<dl>
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<dt><a name="index-STACK_005fCHECK_005fMOVING_005fSP"></a>Macro: <strong>STACK_CHECK_MOVING_SP</strong></dt>
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<dd><p>An integer which is nonzero if GCC should move the stack pointer page by page
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when doing probes. This can be necessary on systems where the stack pointer
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contains the bottom address of the memory area accessible to the executing
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thread at any point in time. In this situation an alternate signal stack
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is required in order to be able to recover from a stack overflow. The
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default value of this macro is zero.
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</p></dd></dl>
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<dl>
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<dt><a name="index-STACK_005fCHECK_005fPROTECT"></a>Macro: <strong>STACK_CHECK_PROTECT</strong></dt>
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<dd><p>The number of bytes of stack needed to recover from a stack overflow, for
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languages where such a recovery is supported. The default value of 4KB/8KB
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with the <code>setjmp</code>/<code>longjmp</code>-based exception handling mechanism and
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8KB/12KB with other exception handling mechanisms should be adequate for most
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architectures and operating systems.
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</p></dd></dl>
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<p>The following macros are relevant only if neither STACK_CHECK_BUILTIN
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nor STACK_CHECK_STATIC_BUILTIN is defined; you can omit them altogether
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in the opposite case.
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</p>
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<dl>
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<dt><a name="index-STACK_005fCHECK_005fMAX_005fFRAME_005fSIZE"></a>Macro: <strong>STACK_CHECK_MAX_FRAME_SIZE</strong></dt>
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<dd><p>The maximum size of a stack frame, in bytes. GCC will generate probe
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instructions in non-leaf functions to ensure at least this many bytes of
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stack are available. If a stack frame is larger than this size, stack
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checking will not be reliable and GCC will issue a warning. The
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default is chosen so that GCC only generates one instruction on most
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systems. You should normally not change the default value of this macro.
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</p></dd></dl>
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<dl>
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<dt><a name="index-STACK_005fCHECK_005fFIXED_005fFRAME_005fSIZE"></a>Macro: <strong>STACK_CHECK_FIXED_FRAME_SIZE</strong></dt>
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<dd><p>GCC uses this value to generate the above warning message. It
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represents the amount of fixed frame used by a function, not including
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space for any callee-saved registers, temporaries and user variables.
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You need only specify an upper bound for this amount and will normally
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use the default of four words.
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</p></dd></dl>
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<dl>
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<dt><a name="index-STACK_005fCHECK_005fMAX_005fVAR_005fSIZE"></a>Macro: <strong>STACK_CHECK_MAX_VAR_SIZE</strong></dt>
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<dd><p>The maximum size, in bytes, of an object that GCC will place in the
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fixed area of the stack frame when the user specifies
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<samp>-fstack-check</samp>.
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GCC computed the default from the values of the above macros and you will
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normally not need to override that default.
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</p></dd></dl>
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<dl>
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<dt><a name="index-TARGET_005fSTACK_005fCLASH_005fPROTECTION_005fFINAL_005fDYNAMIC_005fPROBE"></a>Target Hook: <em>bool</em> <strong>TARGET_STACK_CLASH_PROTECTION_FINAL_DYNAMIC_PROBE</strong> <em>(rtx <var>residual</var>)</em></dt>
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<dd><p>Some targets make optimistic assumptions about the state of stack probing when they emit their prologues. On such targets a probe into the end of any dynamically allocated space is likely required for safety against stack clash style attacks. Define this variable to return nonzero if such a probe is required or zero otherwise. You need not define this macro if it would always have the value zero.
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</p></dd></dl>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Frame-Registers.html#Frame-Registers" accesskey="n" rel="next">Frame Registers</a>, Previous: <a href="Exception-Handling.html#Exception-Handling" accesskey="p" rel="prev">Exception Handling</a>, Up: <a href="Stack-and-Calling.html#Stack-and-Calling" accesskey="u" rel="up">Stack and Calling</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>
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</div>
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