path: root/Documentation/ABI
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authorLinus Torvalds <>2011-07-22 17:05:15 -0700
committerLinus Torvalds <>2011-07-22 17:05:15 -0700
commit8e204874db000928e37199c2db82b7eb8966cc3c (patch)
treeeae66035cb761c3c5a79e98b92280b5156bc01ef /Documentation/ABI
parent3e0b8df79ddb8955d2cce5e858972a9cfe763384 (diff)
parentaafade242ff24fac3aabf61c7861dfa44a3c2445 (diff)
Merge branch 'x86-vdso-for-linus' of git://
* 'x86-vdso-for-linus' of git:// x86-64, vdso: Do not allocate memory for the vDSO clocksource: Change __ARCH_HAS_CLOCKSOURCE_DATA to a CONFIG option x86, vdso: Drop now wrong comment Document the vDSO and add a reference parser ia64: Replace clocksource.fsys_mmio with generic arch data x86-64: Move vread_tsc and vread_hpet into the vDSO clocksource: Replace vread with generic arch data x86-64: Add --no-undefined to vDSO build x86-64: Allow alternative patching in the vDSO x86: Make alternative instruction pointers relative x86-64: Improve vsyscall emulation CS and RIP handling x86-64: Emulate legacy vsyscalls x86-64: Fill unused parts of the vsyscall page with 0xcc x86-64: Remove vsyscall number 3 (venosys) x86-64: Map the HPET NX x86-64: Remove kernel.vsyscall64 sysctl x86-64: Give vvars their own page x86-64: Document some of entry_64.S x86-64: Fix alignment of jiffies variable
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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