Re: [edk2-devel] VariablePolicy: Final Changes Thread 2 - ECC & UnitTest

["Laszlo Ersek" <lersek@redhat.com>]

On 10/07/20 03:46, Michael D Kinney wrote:
>
> Bret,
>
> Initializing variable in declaration for structures and arrays
> introduces use of intrinsics.  Since it is possible for unit test
> sources to be used for both host and target tests, I recommend we
> continue to follow the EDK II coding style for unit tests to support
> maximum compatibility and code reuse.
>
> Using a module global variable with initializers instead of
> initializing a local declaration is the same amount of work, so I do
> not believe that will result in fewer tests.
>
> I agree it is useful to have the test data next to the test code. This
> can be accomplished by breaking up into more files so the test data is
> immediately above the test function the test data is used.  Does ECC
> raise an error if a module global is placed between 2 functions?  A
> 2nd approach to put the module global immediately above the test
> function the test data is used.

Consider the following example structure type, for the sake of
discussion:

  typedef struct {
    UINT32 Value;
  } TEST_DATA;


* Case#1: block scope, automatic storage duration

  EFI_STATUS
  FoobarTest (
    VOID
    )
  {
    TEST_DATA TestData = { 42 };
    // ...
  }

Problem: uses intrinsics.


* Case#2: file scope, static storage duration.

  STATIC CONST TEST_DATA mTestData = { 42 };

  EFI_STATUS
  FoobarTest (
    VOID
    )
  {
    // ...
  }

Problem: either "mTestData" is textually far from FoobarTest(), or -- if
we keep them close to each other -- we mix variable definitions with
function definitions, at file scope.


* Case #3: block scope, static storage duration.

  EFI_STATUS
  FoobarTest (
    VOID
    )
  {
    STATIC CONST TEST_DATA TestData = { 42 };
    // ...
  }

Problem: there should be none. Does not involve intrinsics, and the
object definition is part of the function's scope.


If ECC does not recognize case#3 as valid, then that is an *ECC bug*.

ECC has no reason to prevent case#3, as case#3 does not involve
intrinsics, and is a generally valid and useful C language construct (it
combines the life cycle of case#2 with the visibility of case#1).

Again, if ECC rejects case#3, that's *definitely* a bug in ECC, and we
should fix it first. Given that ECC includes a full-blown C language
parser, the fix should not be too difficult -- check if the declaration
has the "static" storage-class specifier.

... In fact, I think that purely CONST-qualifying TestData might suffice
for shutting up ECC. See the following in
"BaseTools/Source/Python/Ecc/c.py", method
"CheckFuncLayoutLocalVariable":

>         for Result in ResultSet:
>             if len(Result[1]) > 0 and 'CONST' not in Result[3]:
>                 PrintErrorMsg(ERROR_C_FUNCTION_LAYOUT_CHECK_NO_INIT_OF_VARIABLE, 'Variable Name: %s' % Result[0], FileTable, Result[2])

So case#3 should work through that avenue already, because case#3 has
CONST *too*.

Now, in case#3, if "TestData" needs to undergo modifications, and so
CONST is not immediately desirable, that's solvable:

  EFI_STATUS
  FoobarTest (
    VOID
    )
  {
    STATIC CONST TEST_DATA TestDataTemplate = { 42 };
    TEST_DATA TestData;

    CopyMem (&TestData, TestDataTemplate, sizeof (TEST_DATA));
    // ...
  }

Thanks
Laszlo

>
> Best regards,
>
> Mike
>
> From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Bret Barkelew via groups.io
> Sent: Tuesday, October 6, 2020 5:28 PM
> To: devel@edk2.groups.io
> Subject: [edk2-devel] VariablePolicy: Final Changes Thread 2 - ECC & UnitTest
>
> I\x19ve worked through all the ECC issues with Variable Policy (AND the UnitTests) on this branch:
> Commits · corthon/edk2 (github.com)<https://github.com/corthon/edk2/commits/var_policy_dev_submission_v8>
>
> I even wrote the Main() entry point lib that Laszlo suggested (it works rather nicely):
> TEMP: Staging for HostTest entry point · corthon/edk2@4ce5210 (github.com)<https://github.com/corthon/edk2/commit/4ce52108b3e1bcb2ba78995be94c3949fe647eda>
>
> However, there\x19s one that I just can\x19t get past and I would like to take it up with the community. I don\x19t think that UnitTests should have to deal with the \x1ccan\x19t initialize variables in declaration\x1d check. Almost none of the solutions that I tested worked, and the ones that did were too cumbersome. They failed on two key points that are important for test writing:
>
>   *   They were annoying to write ===> fewer tests.
>   *   They moved even more of the test case data away from the test ===> harder to read tests.
>
> I would like to move for an exception for unit tests (or at least host-based unit tests), but I don\x19t know how to accomplish that from a technical standpoint.
>
> Thoughts?
>
> - Bret
>
>
>
>
> 
>
>