"brian m. carlson" <sandals@xxxxxxxxxxxxxxxxxxxx> writes:
> On 2020-08-06 at 23:47:34, Junio C Hamano wrote:
>> I am wondering if it is a good idea to use something like
>>
>> static inline void precompose_argv(int argc, const char **argv)
>> {
>> ; /* nothing */
>> }
>>
>> instead. As long as the compiler is reasonable enough, this should
>> not result in any code change in the result, except that it would
>> still catch wrong arguments, even if these two parameters are unused
>> and optimized out.
>
> Yes, this seems like a prudent approach. I believe it's widely used by
> the Linux kernel, so presumably compilers are capable enough to optimize
> it out. As you noted, it provides type checking for all platforms,
> which is nice.
So I hope the following (untested and not signed off yet) may lead
us in the right direction?
-- >8 --
Subject: compat-util: type-check parameters of mocked functions
When there is no need to run a specific function on certain platforms,
we often #define an empty function to swallow its parameters and
make it into a no-op, e.g.
#define precompose_argv(c,v) /* no-op */
While this guarantees that no unneeded code is generated, it also
discards type and other checks on these parameters, e.g. a new code
written with the argv-array API (diff_args is of type "struct
argv_array" that has .argc and .argv members):
precompose_argv(diff_args.argc, diff_args.argv);
must be updated to use "struct strvec diff_args" with .nr and .v
members, like so:
precompose_argv(diff_args.nr, diff_args.v);
after the argv-array API has been updated to the strvec API.
However, the "no oop" C preprocessor macro is too aggressive to
discard what is unused, and did not catch such a call that was left
unconverted.
Using a "static inline" function whose body is a no-op should still
result in the same binary with decent compilers yet catch such a
reference to a missing field or passing a value of a wrong type.
While at it, I notice that precompute_str() has never been used
anywhere in the code, since it was introduced at 76759c7d (git on
Mac OS and precomposed unicode, 2012-07-08). Instead of turning it
into a static inline, just remove it.
---
git-compat-util.h | 20 +++++++++++++++-----
1 file changed, 15 insertions(+), 5 deletions(-)
diff --git a/git-compat-util.h b/git-compat-util.h
index 5637114b8d..7a0fb7a045 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -252,8 +252,10 @@ typedef unsigned long uintptr_t;
#ifdef PRECOMPOSE_UNICODE
#include "compat/precompose_utf8.h"
#else
-#define precompose_str(in,i_nfd2nfc)
-#define precompose_argv(c,v)
+static inline void precompose_argv(int argc, const char **argv)
+{
+ ; /* nothing */
+}
#define probe_utf8_pathname_composition()
#endif
@@ -270,7 +272,9 @@ struct itimerval {
#endif
#ifdef NO_SETITIMER
-#define setitimer(which,value,ovalue)
+static inline int setitimer(int which, const struct itimerval *value, struct itimerval *newvalue) {
+ ; /* nothing */
+}
#endif
#ifndef NO_LIBGEN_H
@@ -1231,8 +1235,14 @@ int warn_on_fopen_errors(const char *path);
#endif
#ifndef _POSIX_THREAD_SAFE_FUNCTIONS
-#define flockfile(fh)
-#define funlockfile(fh)
+static inline void flockfile(FILE *fh)
+{
+ ; /* nothing */
+}
+static inline void funlockfile(FILE *fh)
+{
+ ; /* nothing */
+}
#define getc_unlocked(fh) getc(fh)
#endif
