Messages in this thread | | | Date | Wed, 08 Nov 2023 19:26:34 -0800 (PST) | Subject | Re: [PATCH] selftests: sud_test: return correct emulated syscall value on RISC-V | From | Palmer Dabbelt <> |
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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:
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. + */ +#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?
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