Re: [XEN PATCH] xen: Drop logic for old clang versions.

[Nicola Vetrini <nicola.vetrini@bugseng.com>]

On 2025-08-11 09:47, Roger Pau Monné wrote:
> On Sun, Aug 10, 2025 at 03:03:53PM +0200, nicola.vetrini@gmail.com 
> wrote:
>> From: Nicola Vetrini <nicola.vetrini@bugseng.com>
>> 
>> The enforced toolchain baseline for clang is version 11,
>> therefore this logic is effectively dead code.
>> 
>> No functional change.
>> 
>> Signed-off-by: Nicola Vetrini <nicola.vetrini@gmail.com>
> 
> Acked-by: Roger Pau Monné <roger.pau@citrix.com>
> 
>> ---
>> Mentioned in https://gitlab.com/xen-project/xen/-/issues/201
>> ---
>>  xen/common/coverage/llvm.c   | 4 ----
>>  xen/include/xen/self-tests.h | 9 +--------
>>  2 files changed, 1 insertion(+), 12 deletions(-)
>> 
>> diff --git a/xen/common/coverage/llvm.c b/xen/common/coverage/llvm.c
>> index 50d7a3c5d301..517b2aa8c202 100644
>> --- a/xen/common/coverage/llvm.c
>> +++ b/xen/common/coverage/llvm.c
>> @@ -44,12 +44,8 @@
>>      ((uint64_t)'f' << 16) | ((uint64_t)'R' << 8)  | ((uint64_t)129)
>>  #endif
>> 
>> -#if __clang_major__ >= 4 || (__clang_major__ == 3 && __clang_minor__ 
>> >= 9)
>>  #define LLVM_PROFILE_VERSION    4
>>  #define LLVM_PROFILE_NUM_KINDS  2
>> -#else
>> -#error "clang version not supported with coverage"
>> -#endif
> 
> Rant: most of the LLVM coverage stuff is already kind of dead code, as
> the format of the data changes between versions and there's no way for
> LLVM to generate the blob itself using a builtin function or
> similar.  We haven't kept up with new formats, and now it's not
> possible to parse the output coverage data when using newish LLVM
> versions.
> 
> Linux converts it's LLVM coverage data to gcov format (which AFAIK is
> way more stable), and exports it in gcov format.  We should consider
> importing that from Linux.
> 
> Thanks, Roger.

Fair point. Generally I found coverage reports generated using LLVM 
tooling a bit more informative than gcov's, but I don't know how much 
work would it be to adapt Xen for newer versions of LLVM.

-- 
Nicola Vetrini, B.Sc.
Software Engineer
BUGSENG (https://bugseng.com)
LinkedIn: https://www.linkedin.com/in/nicola-vetrini-a42471253