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Merge branch 'x86-vdso-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

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* 'x86-vdso-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  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
This commit is contained in:
Linus Torvalds
2011-07-22 17:05:15 -07:00
parent 3e0b8df79d aafade242f
commit 8e204874db
41 changed files with 946 additions and 397 deletions
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Documentation/ABI/stable/vdso
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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,
though.
(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.)