KVM: selftests: Add formatted guest assert support in ucall framework

Add printf-based GUEST_ASSERT macros and accompanying host-side support to
provide an assert-specific versions of GUEST_PRINTF().  To make it easier
to parse assert messages, for humans and bots alike, preserve/use the same
layout as host asserts, e.g. in the example below, the reported expression,
file, line number, and message are from the guest assertion, not the host
reporting of the assertion.

The call stack still captures the host reporting, but capturing the guest
stack is a less pressing concern, i.e. can be done in the future, and an
optimal solution would capture *both* the host and guest stacks, i.e.
capturing the host stack isn't an outright bug.

  Running soft int test
  ==== Test Assertion Failure ====
    x86_64/svm_nested_soft_inject_test.c:39: regs->rip != (unsigned long)l2_guest_code_int
    pid=214104 tid=214104 errno=4 - Interrupted system call
       1	0x0000000000401b35: run_test at svm_nested_soft_inject_test.c:191
       2	0x00000000004017d2: main at svm_nested_soft_inject_test.c:212
       3	0x0000000000415b03: __libc_start_call_main at libc-start.o:?
       4	0x000000000041714f: __libc_start_main_impl at ??:?
       5	0x0000000000401660: _start at ??:?
    Expected IRQ at RIP 0x401e50, received IRQ at 0x401e50

Don't bother sharing code between ucall_assert() and ucall_fmt(), as
forwarding the variable arguments would either require using macros or
building a va_list, i.e. would make the code less readable and/or require
just as much copy+paste code anyways.

Gate the new macros with a flag so that tests can more or less be switched
over one-by-one.  The slow conversion won't be perfect, e.g. library code
won't pick up the flag, but the only asserts in library code are of the
vanilla GUEST_ASSERT() variety, i.e. don't print out variables.

Add a temporary alias to GUEST_ASSERT_1() to fudge around ARM's
arch_timer.h header using GUEST_ASSERT_1(), thus thwarting any attempt to
convert tests one-by-one.

Link: https://lore.kernel.org/r/20230729003643.1053367-9-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

1 files changed, 22 insertions, 0 deletions

diff --git a/tools/testing/selftests/kvm/lib/ucall_common.c b/tools/testing/selftests/kvm/lib/ucall_common.c
index b507db91139b..816a3fa109bf 100644
--- a/tools/testing/selftests/kvm/lib/ucall_common.c
+++ b/tools/testing/selftests/kvm/lib/ucall_common.c
@@ -75,6 +75,28 @@ static void ucall_free(struct ucall *uc)
 	clear_bit(uc - ucall_pool->ucalls, ucall_pool->in_use);
 }
 
+void ucall_assert(uint64_t cmd, const char *exp, const char *file,
+		  unsigned int line, const char *fmt, ...)
+{
+	struct ucall *uc;
+	va_list va;
+
+	uc = ucall_alloc();
+	uc->cmd = cmd;
+
+	WRITE_ONCE(uc->args[GUEST_ERROR_STRING], (uint64_t)(exp));
+	WRITE_ONCE(uc->args[GUEST_FILE], (uint64_t)(file));
+	WRITE_ONCE(uc->args[GUEST_LINE], line);
+
+	va_start(va, fmt);
+	guest_vsnprintf(uc->buffer, UCALL_BUFFER_LEN, fmt, va);
+	va_end(va);
+
+	ucall_arch_do_ucall((vm_vaddr_t)uc->hva);
+
+	ucall_free(uc);
+}
+
 void ucall_fmt(uint64_t cmd, const char *fmt, ...)
 {
 	struct ucall *uc;