As recently pointed out by Thomas, if a register is forced for two
different register variables, among them one is used as "+" (both input
and output) and another is only used as input, Clang would treat the
conflicting input parameters as undefined behaviour and optimize away
the argument assignment.
Instead use "=r" (only output) for the output parameter and "r" (only
input) for the input parameter.
While the example from the GCC documentation uses "0" for the input
parameter, this is not necessary as confirmed by the GCC developers and "r"
matches what the other architectures' vDSO implementations are using.
[ alex: Update log to match v2 (Thomas) ]
Link: https://lore.kernel.org/all/20250603-loongarch-vdso-syscall-v1-1-6d12d6dfbdd0@linutronix.de/
Link: https://gcc.gnu.org/onlinedocs/gcc-15.1.0/gcc/Local-Register-Variables.html
Link: https://gcc.gnu.org/pipermail/gcc-help/2025-June/144266.html
Cc: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Cc: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Xi Ruoyao <xry111@xry111.site>
Reviewed-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Fixes: ee0d03053e ("RISC-V: vDSO: Wire up getrandom() vDSO")
Link: https://lore.kernel.org/r/20250606092443.73650-2-xry111@xry111.site
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Signed-off-by: Palmer Dabbelt <palmer@dabbelt.com>
Hook up the generic vDSO implementation to the generic vDSO getrandom
implementation by providing the required __arch_chacha20_blocks_nostack
and getrandom_syscall implementations. Also wire up the selftests.
The benchmark result:
vdso: 25000000 times in 2.466341333 seconds
libc: 25000000 times in 41.447720005 seconds
syscall: 25000000 times in 41.043926672 seconds
vdso: 25000000 x 256 times in 162.286219353 seconds
libc: 25000000 x 256 times in 2953.855018685 seconds
syscall: 25000000 x 256 times in 2796.268546000 seconds
[ alex: - Fix dynamic relocation
- Squash Nathan's fix https://lore.kernel.org/all/20250423-riscv-fix-compat_vdso-lld-v2-1-b7bbbc244501@kernel.org/
- Add comment from Loongarch ]
Signed-off-by: Xi Ruoyao <xry111@xry111.site>
Link: https://lore.kernel.org/r/20250411024600.16045-1-xry111@xry111.site
Tested-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Signed-off-by: Palmer Dabbelt <palmer@dabbelt.com>
