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- What: vDSO
- Date: July 2011
- KernelVersion: 3.0
- Contact: Andy Lutomirski <luto@kernel.org>
- Description:
- 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 according to your platform's ABI. On many
- platforms they are called just like ordinary C function. On other platforms
- (ex: powerpc) they are called with the same convention as system calls which
- is different from ordinary C functions. 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
- tools/testing/selftests/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.
- Note:
- 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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