On Thu, 09 Nov 2023 00:22:46 PST (-0800), cleger@rivosinc.com wrote:
On 09/11/2023 04:26, Palmer Dabbelt wrote:
On Wed, 13 Sep 2023 07:07:11 PDT (-0700), cleger@rivosinc.com wrote:
Currently, the sud_test expects the emulated syscall to return the emulated syscall number. This assumption only works on architectures were the syscall calling convention use the same register for syscall number/syscall return value. This is not the case for RISC-V and thus the return value must be also emulated using the provided ucontext.
Signed-off-by: Clément Léger cleger@rivosinc.com
tools/testing/selftests/syscall_user_dispatch/sud_test.c | 8 ++++++++ 1 file changed, 8 insertions(+)
diff --git a/tools/testing/selftests/syscall_user_dispatch/sud_test.c b/tools/testing/selftests/syscall_user_dispatch/sud_test.c index b5d592d4099e..1b5553c19700 100644 --- a/tools/testing/selftests/syscall_user_dispatch/sud_test.c +++ b/tools/testing/selftests/syscall_user_dispatch/sud_test.c @@ -158,6 +158,14 @@ static void handle_sigsys(int sig, siginfo_t *info, void *ucontext)
/* In preparation for sigreturn. */ SYSCALL_DISPATCH_OFF(glob_sel);
+ /* + * Modify interrupted context returned value according to syscall + * calling convention + */ +#if defined(__riscv) + ((ucontext_t*)ucontext)->uc_mcontext.__gregs[REG_A0] = MAGIC_SYSCALL_1; +#endif }
TEST(dispatch_and_return)
I'm not sure if I'm just tired, but it took me a while to figure out why this was necessary. I think this is a better explanation:
I think it's because this mechanism does not behave like other syscalls at all and the classic calling convention does not really apply...
Yep. I also got tripped up because I mis-read the docs and though SIGSYS was only for some error case (where it's actually for all the intercepted syscalls).
diff --git a/tools/testing/selftests/syscall_user_dispatch/sud_test.c b/tools/testing/selftests/syscall_user_dispatch/sud_test.c index b5d592d4099e..a913fd90cfa3 100644 --- a/tools/testing/selftests/syscall_user_dispatch/sud_test.c +++ b/tools/testing/selftests/syscall_user_dispatch/sud_test.c @@ -158,6 +158,16 @@ static void handle_sigsys(int sig, siginfo_t *info, void *ucontext) /* In preparation for sigreturn. */ SYSCALL_DISPATCH_OFF(glob_sel); + /* + * The tests for argument handling assume that `syscall(x) == x`. This + * is a NOP on x86 because the syscall number is passed in %rax, which + * happens to also be the function ABI return register. Other + * architectures may need to swizzle the arguments around. + */
Indeed, that is more clear. Should I send a v2 ?
I would, but +Thomas as it looks like he's the one taking patches for this.
+#if defined(__riscv) + (ucontext_t*)ucontext)->uc_mcontext.__gregs[REG_A0] = + (ucontext_t*)ucontext)->uc_mcontext.__gregs[REG_A7]; +#endif } TEST(dispatch_and_return)
but also
Reviewed-by: Palmer Dabbelt palmer@rivosinc.com Acked-by: Palmer Dabbelt palmer@rivosinc.com
as I agree this is correct.
also: wouldn't arm64 also need to move x8 into x0 here, for essentially the same reason as we do?
Yes, as well as for a bunch of other architectures. I suspect this has only been tested on x86. AFAIK, this feature is mainly for wine usage which then makes sense for x86 and games.
Ya, makes sense -- I'd just looked at Arm to double-check my understanding here, as we usually don't find bugs in generic code before Arm does.
Thanks,
Clément