[PATCH] KVM: selftests: Treat %llx like %lx when formatting guest printf

[PATCH] KVM: selftests: Treat %llx like %lx when formatting guest printf

[Sean Christopherson]

Treat %ll* formats the same as %l* formats when processing printfs from
the guest so that using e.g. %llx instead of %lx generates the expected
output.  Ideally, unexpected formats would generate compile-time warnings
or errors, but it's not at all obvious how to actually accomplish that.

Alternatively, guest_vsnprintf() could assert on an unexpected format,
but since the vast majority of printfs are for failed guest asserts,
getting *something* printed is better than nothing.

E.g. before

 ==== Test Assertion Failure ====
  x86_64/private_mem_conversions_test.c:265: mem[i] == 0
  pid=4286 tid=4290 errno=4 - Interrupted system call
     1	0x0000000000401c74: __test_mem_conversions at private_mem_conversions_test.c:336
     2	0x00007f3aae6076da: ?? ??:0
     3	0x00007f3aae32161e: ?? ??:0
  Expected 0x0 at offset 0 (gpa 0x%lx), got 0x0

and after

 ==== Test Assertion Failure ====
  x86_64/private_mem_conversions_test.c:265: mem[i] == 0
  pid=5664 tid=5668 errno=4 - Interrupted system call
     1	0x0000000000401c74: __test_mem_conversions at private_mem_conversions_test.c:336
     2	0x00007fbe180076da: ?? ??:0
     3	0x00007fbe17d2161e: ?? ??:0
  Expected 0x0 at offset 0 (gpa 0x100000000), got 0xcc

Fixes: e5119382499c ("KVM: selftests: Add guest_snprintf() to KVM selftests")
Cc: Aaron Lewis <aaronlewis@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 tools/testing/selftests/kvm/lib/guest_sprintf.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/tools/testing/selftests/kvm/lib/guest_sprintf.c b/tools/testing/selftests/kvm/lib/guest_sprintf.c
index c4a69d8aeb68..74627514c4d4 100644
--- a/tools/testing/selftests/kvm/lib/guest_sprintf.c
+++ b/tools/testing/selftests/kvm/lib/guest_sprintf.c
@@ -200,6 +200,13 @@ int guest_vsnprintf(char *buf, int n, const char *fmt, va_list args)
 			++fmt;
 		}
 
+		/*
+		 * Play nice with %llu, %llx, etc.  KVM selftests only support
+		 * 64-bit builds, so just treat %ll* the same as %l*.
+		 */
+		if (qualifier == 'l' && *fmt == 'l')
+			++fmt;
+
 		/* default base */
 		base = 10;
 

base-commit: 7c7cce2cf7ee2ac54851ba1fbcf0e968932e32b9
-- 
2.42.0.515.g380fc7ccd1-goog

Re: [PATCH] KVM: selftests: Treat %llx like %lx when formatting guest printf

[Sean Christopherson]

On Thu, 21 Sep 2023 10:16:41 -0700, Sean Christopherson wrote:
> Treat %ll* formats the same as %l* formats when processing printfs from
> the guest so that using e.g. %llx instead of %lx generates the expected
> output.  Ideally, unexpected formats would generate compile-time warnings
> or errors, but it's not at all obvious how to actually accomplish that.
> 
> Alternatively, guest_vsnprintf() could assert on an unexpected format,
> but since the vast majority of printfs are for failed guest asserts,
> getting *something* printed is better than nothing.
> 
> [...]

Applied to kvm-x86 selftests, thanks!

[1/1] KVM: selftests: Treat %llx like %lx when formatting guest printf
      https://github.com/kvm-x86/linux/commit/b15e7490a1ef

--
https://github.com/kvm-x86/linux/tree/next