On 10/10/2023 03:56, Stefano Stabellini wrote:
On Fri, 6 Oct 2023, Nicola Vetrini wrote:
Given the following macros in <xen/perfc.h> and
#define perfc_incra(x,y)
\
( (y) <= PERFC_LAST_ ## x - PERFC_ ## x ?
\
++this_cpu(perfcounters)[PERFC_ ## x + (y)] : 0 )
and the following violation
xen/arch/arm/traps.c:1407.5-1407.32:
reference to enum constant `PERFC_hypercalls' has essential type
`enum
perfcounter'
and standard type `int'
<preprocessed xen/arch/arm/traps.c>:11606.29-11606.44: preprocessed
tokens
<scratch space>:137.1-137.16: expanded from macro `PERFC_'
xen/include/xen/perfc.h:69.35-69.45: expanded from macro
`perfc_incra'
xen/arch/arm/traps.c:1407.5-1407.32:
`+' addition operator expects a number or a character
<preprocessed xen/arch/arm/traps.c>:11606.46: preprocessed tokens
xen/include/xen/perfc.h:69.47: expanded from macro `perfc_incra'
the difference between enumerated values is forbidden by the Rule. In
the
coding standard's
interpretation, named enums are unordered list of symbols, which can
only be
compared for
equality.
There are a few possible paths forward:
1. use means different from named enums to generate these constants
(such as
#define-s or
constants integers);
This is a viable option
2. explicitly deviate subtraction of enums, therefore defining an
explicit
ordering on
enumerated values;
I would prefer to avoid a project-wide deviation, because I think in
general it is a good rule to have. If we go with a deviation, I think
it
would be better to deviate PERFCOUNTER or perfc.h specifically. This is
a file that changes very rarely. We could make the case that this is
safe with GCC (most probably is) and this case was reviewed carefully
and doesn't change often (3 changes in the last 10 yeas).
3. use an unnamed enum, effectively considering the enumerated values
as plain
integers.
This does not violate the Rule.
What do you mean by unname enum?
e.g.
enum {
#include <xen/perfc_defn.h>
NUM_PERFCOUNTERS
};
instead of
enum perfcounter {
#include <xen/perfc_defn.h>
NUM_PERFCOUNTERS
};
--
Nicola Vetrini, BSc
Software Engineer, BUGSENG srl (https://bugseng.com)