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author | Linus Torvalds <torvalds@linux-foundation.org> | 2011-07-23 00:05:15 (GMT) |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2011-07-23 00:05:15 (GMT) |
commit | 8e204874db000928e37199c2db82b7eb8966cc3c (patch) | |
tree | eae66035cb761c3c5a79e98b92280b5156bc01ef /Documentation/ABI | |
parent | 3e0b8df79ddb8955d2cce5e858972a9cfe763384 (diff) | |
parent | aafade242ff24fac3aabf61c7861dfa44a3c2445 (diff) | |
download | linux-8e204874db000928e37199c2db82b7eb8966cc3c.tar.xz |
Merge branch 'x86-vdso-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip
* '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
Diffstat (limited to 'Documentation/ABI')
-rw-r--r-- | Documentation/ABI/stable/vdso | 27 |
1 files changed, 27 insertions, 0 deletions
diff --git a/Documentation/ABI/stable/vdso b/Documentation/ABI/stable/vdso new file mode 100644 index 0000000..8a1cbb5 --- /dev/null +++ b/Documentation/ABI/stable/vdso @@ -0,0 +1,27 @@ +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.)
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