diff options
Diffstat (limited to 'Documentation/ABI/stable/vdso')
| -rw-r--r-- | Documentation/ABI/stable/vdso | 35 |
1 files changed, 35 insertions, 0 deletions
diff --git a/Documentation/ABI/stable/vdso b/Documentation/ABI/stable/vdso new file mode 100644 index 000000000..951838d42 --- /dev/null +++ b/Documentation/ABI/stable/vdso @@ -0,0 +1,35 @@ +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 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 +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. |