From 67820470cc94be2472feae65eb8b7b02433b7b2d Mon Sep 17 00:00:00 2001 From: Cornelius Diekmann Date: Thu, 10 Aug 2017 14:55:35 +0200 Subject: [PATCH] Clarify: vDSO is linked automatically with glibc Change is partly a verbatim copy of https://www.kernel.org/doc/Documentation/ABI/stable/vdso Quote: "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." The old version of the book was slightly imprecise. It was unclear to me whether this is an optional or a default behavior. --- SysCall/syscall-3.md | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/SysCall/syscall-3.md b/SysCall/syscall-3.md index ac47a25..79474dc 100644 --- a/SysCall/syscall-3.md +++ b/SysCall/syscall-3.md @@ -230,7 +230,7 @@ That's all. Now let's look on the modern concept - `vDSO`. Introduction to vDSO -------------------------------------------------------------------------------- -As I already wrote above, `vsyscall` is an obsolete concept and replaced by the `vDSO` or `virtual dynamic shared object`. The main difference between the `vsyscall` and `vDSO` mechanisms is that `vDSO` maps memory pages into each process in a shared object [form](https://en.wikipedia.org/wiki/Library_%28computing%29#Shared_libraries), but `vsyscall` is static in memory and has the same address every time. For the `x86_64` architecture it is called -`linux-vdso.so.1`. All userspace applications linked with this shared library via the `glibc`. For example: +As I already wrote above, `vsyscall` is an obsolete concept and replaced by the `vDSO` or `virtual dynamic shared object`. The main difference between the `vsyscall` and `vDSO` mechanisms is that `vDSO` maps memory pages into each process in a shared object [form](https://en.wikipedia.org/wiki/Library_%28computing%29#Shared_libraries), but `vsyscall` is static in memory and has the same address every time. For the `x86_64` architecture it is called -`linux-vdso.so.1`. All userspace applications that dynamically link to `glibc` will use the `vDSO` automatically. For example: ``` ~$ ldd /bin/uname