These need to be bit-exact following exactly what is shown in the
assembly.
libunwind parses where EIP is to see if it is in a stack frame.
Also needsto live in VDSO otherwise backtrace doesn't work.
Fairly straightforward, just requires enabling lld in this case since
cross-compiling doesn't work well with gnu linker.
Also lld doesn't understand the linker script program header symbolic
names for read/write/execute. So we need to use the raw number there.
Works around an issue where GCC 11 generates broken `init_array` section
and also plt sections that glibc doesn't understand.
The `mov ebp, ecx` was breaking vsyscall and was expected to be used
with the `syscall` instruction rather than `int 0x80`.
Remove that to fix it.
Also remove the pushes and pops around the syscall instruction, these
are unnecessary in an emulated environment, we won't clobber the
registers.
Fixes Steam execution with VDSO.
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
