1GETAUXVAL(3) Linux Programmer's Manual GETAUXVAL(3)
2
6 getauxval - retrieve a value from the auxiliary vector
7
9 #include <sys/auxv.h>
10 unsigned long getauxval(unsigned long type);
12
14 The getauxval() function retrieves values from the auxiliary vector, a
15 mechanism that the kernel's ELF binary loader uses to pass certain in‐
16 formation to user space when a program is executed.
17 Each entry in the auxiliary vector consists of a pair of values: a type
19 that identifies what this entry represents, and a value for that type.
20 Given the argument type, getauxval() returns the corresponding value.
21 The value returned for each type is given in the following list. Not
23 all type values are present on all architectures.
24 AT_BASE
26 The base address of the program interpreter (usually, the dy‐
27 namic linker).
28 AT_BASE_PLATFORM
30 A pointer to a string (PowerPC and MIPS only). On PowerPC, this
31 identifies the real platform; may differ from AT_PLATFORM. On
32 MIPS, this identifies the ISA level (since Linux 5.7).
33 AT_CLKTCK
35 The frequency with which times(2) counts. This value can also
36 be obtained via sysconf(_SC_CLK_TCK).
37 AT_DCACHEBSIZE
39 The data cache block size.
40 AT_EGID
42 The effective group ID of the thread.
43 AT_ENTRY
45 The entry address of the executable.
46 AT_EUID
48 The effective user ID of the thread.
49 AT_EXECFD
51 File descriptor of program.
52 AT_EXECFN
54 A pointer to a string containing the pathname used to execute
55 the program.
56 AT_FLAGS
58 Flags (unused).
59 AT_FPUCW
61 Used FPU control word (SuperH architecture only). This gives
62 some information about the FPU initialization performed by the
63 kernel.
64 AT_GID The real group ID of the thread.
66 AT_HWCAP
68 An architecture and ABI dependent bit-mask whose settings indi‐
69 cate detailed processor capabilities. The contents of the bit
70 mask are hardware dependent (for example, see the kernel source
71 file arch/x86/include/asm/cpufeature.h for details relating to
72 the Intel x86 architecture; the value returned is the first
73 32-bit word of the array described there). A human-readable
74 version of the same information is available via /proc/cpuinfo.
75 AT_HWCAP2 (since glibc 2.18)
77 Further machine-dependent hints about processor capabilities.
78 AT_ICACHEBSIZE
80 The instruction cache block size.
81 AT_L1D_CACHEGEOMETRY
83 Geometry of the L1 data cache, encoded with the cache line size
84 in bytes in the bottom 16 bits and the cache associativity in
85 the next 16 bits. The associativity is such that if N is the
86 16-bit value, the cache is N-way set associative.
87 AT_L1D_CACHESIZE
89 The L1 data cache size.
90 AT_L1I_CACHEGEOMETRY
92 Geometry of the L1 instruction cache, encoded as for
93 AT_L1D_CACHEGEOMETRY.
94 AT_L1I_CACHESIZE
96 The L1 instruction cache size.
97 AT_L2_CACHEGEOMETRY
99 Geometry of the L2 cache, encoded as for AT_L1D_CACHEGEOMETRY.
100 AT_L2_CACHESIZE
102 The L2 cache size.
103 AT_L3_CACHEGEOMETRY
105 Geometry of the L3 cache, encoded as for AT_L1D_CACHEGEOMETRY.
106 AT_L3_CACHESIZE
108 The L3 cache size.
109 AT_PAGESZ
111 The system page size (the same value returned by sysconf(_SC_PA‐
112 GESIZE)).
113 AT_PHDR
115 The address of the program headers of the executable.
116 AT_PHENT
118 The size of program header entry.
119 AT_PHNUM
121 The number of program headers.
122 AT_PLATFORM
124 A pointer to a string that identifies the hardware platform that
125 the program is running on. The dynamic linker uses this in the
126 interpretation of rpath values.
127 AT_RANDOM
129 The address of sixteen bytes containing a random value.
130 AT_SECURE
132 Has a nonzero value if this executable should be treated se‐
133 curely. Most commonly, a nonzero value indicates that the
134 process is executing a set-user-ID or set-group-ID binary (so
135 that its real and effective UIDs or GIDs differ from one an‐
136 other), or that it gained capabilities by executing a binary
137 file that has capabilities (see capabilities(7)). Alterna‐
138 tively, a nonzero value may be triggered by a Linux Security
139 Module. When this value is nonzero, the dynamic linker disables
140 the use of certain environment variables (see ld-linux.so(8))
141 and glibc changes other aspects of its behavior. (See also se‐
142 cure_getenv(3).)
143 AT_SYSINFO
145 The entry point to the system call function in the vDSO. Not
146 present/needed on all architectures (e.g., absent on x86-64).
147 AT_SYSINFO_EHDR
149 The address of a page containing the virtual Dynamic Shared Ob‐
150 ject (vDSO) that the kernel creates in order to provide fast im‐
151 plementations of certain system calls.
152 AT_UCACHEBSIZE
154 The unified cache block size.
155 AT_UID The real user ID of the thread.
157
159 On success, getauxval() returns the value corresponding to type. If
160 type is not found, 0 is returned.
161
163 ENOENT (since glibc 2.19)
164 No entry corresponding to type could be found in the auxiliary
165 vector.
166
168 The getauxval() function was added to glibc in version 2.16.
169
171 For an explanation of the terms used in this section, see at‐
172 tributes(7).
173 ┌────────────┬───────────────┬─────────┐
175 │Interface │ Attribute │ Value │
176 ├────────────┼───────────────┼─────────┤
177 │getauxval() │ Thread safety │ MT-Safe │
178 └────────────┴───────────────┴─────────┘
180 This function is a nonstandard glibc extension.
181
183 The primary consumer of the information in the auxiliary vector is the
184 dynamic linker, ld-linux.so(8). The auxiliary vector is a convenient
185 and efficient shortcut that allows the kernel to communicate a certain
186 set of standard information that the dynamic linker usually or always
187 needs. In some cases, the same information could be obtained by system
188 calls, but using the auxiliary vector is cheaper.
189 The auxiliary vector resides just above the argument list and environ‐
191 ment in the process address space. The auxiliary vector supplied to a
192 program can be viewed by setting the LD_SHOW_AUXV environment variable
193 when running a program:
194 $ LD_SHOW_AUXV=1 sleep 1
196 The auxiliary vector of any process can (subject to file permissions)
198 be obtained via /proc/[pid]/auxv; see proc(5) for more information.
199
201 Before the addition of the ENOENT error in glibc 2.19, there was no way
202 to unambiguously distinguish the case where type could not be found
203 from the case where the value corresponding to type was zero.
204
206 secure_getenv(3), vdso(7), ld-linux.so(8)
207
209 This page is part of release 5.10 of the Linux man-pages project. A
210 description of the project, information about reporting bugs, and the
211 latest version of this page, can be found at
212 https://www.kernel.org/doc/man-pages/.
213GNU 2020-06-09 GETAUXVAL(3)