diff options
Diffstat (limited to 'share/doc/gcc/BPF-Built_002din-Functions.html')
| -rw-r--r-- | share/doc/gcc/BPF-Built_002din-Functions.html | 200 |
1 files changed, 200 insertions, 0 deletions
diff --git a/share/doc/gcc/BPF-Built_002din-Functions.html b/share/doc/gcc/BPF-Built_002din-Functions.html new file mode 100644 index 0000000..f27e840 --- /dev/null +++ b/share/doc/gcc/BPF-Built_002din-Functions.html @@ -0,0 +1,200 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- This file documents the use of the GNU compilers. + +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>Using the GNU Compiler Collection (GCC): BPF Built-in Functions</title> + +<meta name="description" content="Using the GNU Compiler Collection (GCC): BPF Built-in Functions"> +<meta name="keywords" content="Using the GNU Compiler Collection (GCC): BPF Built-in Functions"> +<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="Indices.html#Indices" rel="index" title="Indices"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="Target-Builtins.html#Target-Builtins" rel="up" title="Target Builtins"> +<link href="FR_002dV-Built_002din-Functions.html#FR_002dV-Built_002din-Functions" rel="next" title="FR-V Built-in Functions"> +<link href="Blackfin-Built_002din-Functions.html#Blackfin-Built_002din-Functions" rel="previous" title="Blackfin Built-in Functions"> +<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_US" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> +<a name="BPF-Built_002din-Functions"></a> +<div class="header"> +<p> +Next: <a href="FR_002dV-Built_002din-Functions.html#FR_002dV-Built_002din-Functions" accesskey="n" rel="next">FR-V Built-in Functions</a>, Previous: <a href="Blackfin-Built_002din-Functions.html#Blackfin-Built_002din-Functions" accesskey="p" rel="previous">Blackfin Built-in Functions</a>, Up: <a href="Target-Builtins.html#Target-Builtins" accesskey="u" rel="up">Target Builtins</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html#Indices" title="Index" rel="index">Index</a>]</p> +</div> +<hr> +<a name="BPF-Built_002din-Functions-1"></a> +<h4 class="subsection">6.60.12 BPF Built-in Functions</h4> + +<p>The following built-in functions are available for eBPF targets. +</p> +<dl> +<dt><a name="index-_005f_005fbuiltin_005fbpf_005fload_005fbyte"></a>Built-in Function: <em>unsigned long long</em> <strong>__builtin_bpf_load_byte</strong> <em>(unsigned long long <var>offset</var>)</em></dt> +<dd><p>Load a byte from the <code>struct sk_buff</code> packet data pointed by the register <code>%r6</code> and return it. +</p></dd></dl> + +<dl> +<dt><a name="index-_005f_005fbuiltin_005fbpf_005fload_005fhalf"></a>Built-in Function: <em>unsigned long long</em> <strong>__builtin_bpf_load_half</strong> <em>(unsigned long long <var>offset</var>)</em></dt> +<dd><p>Load 16 bits from the <code>struct sk_buff</code> packet data pointed by the register <code>%r6</code> and return it. +</p></dd></dl> + +<dl> +<dt><a name="index-_005f_005fbuiltin_005fbpf_005fload_005fword"></a>Built-in Function: <em>unsigned long long</em> <strong>__builtin_bpf_load_word</strong> <em>(unsigned long long <var>offset</var>)</em></dt> +<dd><p>Load 32 bits from the <code>struct sk_buff</code> packet data pointed by the register <code>%r6</code> and return it. +</p></dd></dl> + +<dl> +<dt><a name="index-_005f_005fbuiltin_005fpreserve_005faccess_005findex"></a>Built-in Function: <em>void *</em> <strong>__builtin_preserve_access_index</strong> <em>(<var>expr</var>)</em></dt> +<dd><p>BPF Compile Once-Run Everywhere (CO-RE) support. Instruct GCC to generate CO-RE relocation records for any accesses to aggregate data structures (struct, union, array types) in <var>expr</var>. This builtin is otherwise transparent, the return value is whatever <var>expr</var> evaluates to. It is also overloaded: <var>expr</var> may be of any type (not necessarily a pointer), the return type is the same. Has no effect if <code>-mco-re</code> is not in effect (either specified or implied). +</p></dd></dl> + +<dl> +<dt><a name="index-_005f_005fbuiltin_005fpreserve_005ffield_005finfo"></a>Built-in Function: <em>unsigned int</em> <strong>__builtin_preserve_field_info</strong> <em>(<var>expr</var>, unsigned int <var>kind</var>)</em></dt> +<dd><p>BPF Compile Once-Run Everywhere (CO-RE) support. This builtin is used to +extract information to aid in struct/union relocations. <var>expr</var> is +an access to a field of a struct or union. Depending on <var>kind</var>, different +information is returned to the program. A CO-RE relocation for the access in +<var>expr</var> with kind <var>kind</var> is recorded if <code>-mco-re</code> is in effect. +</p> +<p>The following values are supported for <var>kind</var>: +</p><dl compact="compact"> +<dt><code>FIELD_BYTE_OFFSET = 0</code></dt> +<dd><p>The returned value is the offset, in bytes, of the field from the +beginning of the containing structure. For bit-fields, this is the byte offset +of the containing word. +</p> +</dd> +<dt><code>FIELD_BYTE_SIZE = 1</code></dt> +<dd><p>The returned value is the size, in bytes, of the field. For bit-fields, +this is the size in bytes of the containing word. +</p> +</dd> +<dt><code>FIELD_EXISTENCE = 2</code></dt> +<dd><p>The returned value is 1 if the field exists, 0 otherwise. Always 1 at +compile time. +</p> +</dd> +<dt><code>FIELD_SIGNEDNESS = 3</code></dt> +<dd><p>The returned value is 1 if the field is signed, 0 otherwise. +</p> +</dd> +<dt><code>FIELD_LSHIFT_U64 = 4</code></dt> +<dt><code>FIELD_RSHIFT_U64 = 5</code></dt> +<dd><p>The returned value is the number of bits of left- or right-shifting +(respectively) needed in order to recover the original value of the field, +after it has been loaded by a read of <code>FIELD_BYTE_SIZE</code> bytes into an +unsigned 64-bit value. Primarily useful for reading bit-field values +from structures that may change between kernel versions. +</p> +</dd> +</dl> + +<p>Note that the return value is a constant which is known at +compile time. If the field has a variable offset then +<code>FIELD_BYTE_OFFSET</code>, <code>FIELD_LSHIFT_U64</code>, +and <code>FIELD_RSHIFT_U64</code> are not supported. +Similarly, if the field has a variable size then +<code>FIELD_BYTE_SIZE</code>, <code>FIELD_LSHIFT_U64</code>, +and <code>FIELD_RSHIFT_U64</code> are not supported. +</p> +<p>For example, <code>__builtin_preserve_field_info</code> can be used to reliably +extract bit-field values from a structure that may change between +kernel versions: +</p> +<div class="smallexample"> +<pre class="smallexample">struct S +{ + short a; + int x:7; + int y:5; +}; + +int +read_y (struct S *arg) +{ + unsigned long long val; + unsigned int offset + = __builtin_preserve_field_info (arg->y, FIELD_BYTE_OFFSET); + unsigned int size + = __builtin_preserve_field_info (arg->y, FIELD_BYTE_SIZE); + + /* Read size bytes from arg + offset into val. */ + bpf_probe_read (&val, size, arg + offset); + + val <<= __builtin_preserve_field_info (arg->y, FIELD_LSHIFT_U64); + + if (__builtin_preserve_field_info (arg->y, FIELD_SIGNEDNESS)) + val = ((long long) val + >> __builtin_preserve_field_info (arg->y, FIELD_RSHIFT_U64)); + else + val >>= __builtin_preserve_field_info (arg->y, FIELD_RSHIFT_U64); + + return val; +} + +</pre></div> +</dd></dl> + +<hr> +<div class="header"> +<p> +Next: <a href="FR_002dV-Built_002din-Functions.html#FR_002dV-Built_002din-Functions" accesskey="n" rel="next">FR-V Built-in Functions</a>, Previous: <a href="Blackfin-Built_002din-Functions.html#Blackfin-Built_002din-Functions" accesskey="p" rel="previous">Blackfin Built-in Functions</a>, Up: <a href="Target-Builtins.html#Target-Builtins" accesskey="u" rel="up">Target Builtins</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html#Indices" title="Index" rel="index">Index</a>]</p> +</div> + + + +</body> +</html> |