VDSO is heavily abused by Proton games to the point it is showing up as
CPU time.
Implement a guest-facing only thunk library using the hardcoded VDSO
interface in Thunks.
If available this will always be loaded on application load and set the
auxv value to support it.
This requires a bit of special treatment as our first user of linker
scripts since the format of the ELF must be careful crafted to not break
applications trying to parse it.
This library exposes a handful of symbols:
- clock_gettime
- clock_getres
- gettimeofday
- time
- getcpu
- All previous with `__vdso_` prefix
- LINUX_2.6
All of these symbols get routed directly to the host architecture VDSO
interface if they exist.
AArch64 doesn't have getcpu or time VDSO.
In a microbench, VDSO improved bench times substantially
x86-64 host: 3.612s -> 1.369s - 2.63x speed
AArch64 host: 3.821s -> 2.284s - 1.67x speed
- AArch64 isn't as improved due to missing VDSO symbols
This is also our first /always/ enabled thunk as long as the file exists
