path: root/Documentation/ABI/stable/vdso
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authorAnton Arapov <>2012-04-16 10:05:28 +0200
committerAnton Arapov <>2012-04-16 10:05:28 +0200
commitb4b6116a13633898cf868f2f103c96a90c4c20f8 (patch)
tree93d1b7e2cfcdf473d8d4ff3ad141fa864f8491f6 /Documentation/ABI/stable/vdso
parentedd4be777c953e5faafc80d091d3084b4343f5d3 (diff)
fedora kernel: d9aad82f3319f3cfd1aebc01234254ef0c37ad84v3.3.2-1
Signed-off-by: Anton Arapov <>
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+On some architectures, when the kernel loads any userspace program it
+maps an ELF DSO into that program's address space. This DSO is called
+the vDSO and it often contains useful and highly-optimized alternatives
+to real syscalls.
+These functions are called just like ordinary C function according to
+your platform's ABI. Call them from a sensible context. (For example,
+if you set CS on x86 to something strange, the vDSO functions are
+within their rights to crash.) In addition, if you pass a bad
+pointer to a vDSO function, you might get SIGSEGV instead of -EFAULT.
+To find the DSO, parse the auxiliary vector passed to the program's
+entry point. The AT_SYSINFO_EHDR entry will point to the vDSO.
+The vDSO uses symbol versioning; whenever you request a symbol from the
+vDSO, specify the version you are expecting.
+Programs that dynamically link to glibc will use the vDSO automatically.
+Otherwise, you can use the reference parser in Documentation/vDSO/parse_vdso.c.
+Unless otherwise noted, the set of symbols with any given version and the
+ABI of those symbols is considered stable. It may vary across architectures,
+(As of this writing, this ABI documentation as been confirmed for x86_64.
+ The maintainers of the other vDSO-using architectures should confirm
+ that it is correct for their architecture.) \ No newline at end of file