[ruby-core:103395] [Ruby master Bug#17793] `shorten-64-to-32` error for 32-bit Android due to `struct stat` definition

Issue #17793 has been updated by xtkoba (Tee KOBAYASHI).


It makes no difference because neither `SIZEOF_DEVT` nor `SIZEOF_DEV_T` is defined on Android (both for 32- and 64-bit). Is this as expected?

For armv7a-android16:
```
$ clang (...snip...) -o file.o -c ../file.c -Wundef
../file.c:580:34: warning: 'SIZEOF_DEV_T' is not defined, evaluates to 0 [-Wundef]
#if SIZEOF_STRUCT_STAT_ST_DEV <= SIZEOF_DEV_T
                                 ^
../file.c:756:36: warning: 'SIZEOF_DEV_T' is not defined, evaluates to 0 [-Wundef]
# if SIZEOF_STRUCT_STAT_ST_RDEV <= SIZEOF_DEV_T
                                   ^
../file.c:6269:5: warning: 'SIZEOF_DEV_T' is not defined, evaluates to 0 [-Wundef]
#if SIZEOF_DEV_T > SIZEOF_INT
    ^
3 warnings generated.
```

For aarch64-android21:
```
$ clang (...snip...) -o file.o -c ../file.c -Wundef
../file.c:580:5: warning: 'SIZEOF_DEV_T' is not defined, evaluates to 0 [-Wundef]
#if SIZEOF_STRUCT_STAT_ST_DEV <= SIZEOF_DEV_T
    ^
.ext/include/aarch64-linux-android/ruby/config.h:170:35: note: expanded from macro 'SIZEOF_STRUCT_STAT_ST_DEV'
#define SIZEOF_STRUCT_STAT_ST_DEV SIZEOF_DEV_T
                                  ^
../file.c:580:34: warning: 'SIZEOF_DEV_T' is not defined, evaluates to 0 [-Wundef]
#if SIZEOF_STRUCT_STAT_ST_DEV <= SIZEOF_DEV_T
                                 ^
../file.c:756:6: warning: 'SIZEOF_DEV_T' is not defined, evaluates to 0 [-Wundef]
# if SIZEOF_STRUCT_STAT_ST_RDEV <= SIZEOF_DEV_T
     ^
.ext/include/aarch64-linux-android/ruby/config.h:171:36: note: expanded from macro 'SIZEOF_STRUCT_STAT_ST_RDEV'
#define SIZEOF_STRUCT_STAT_ST_RDEV SIZEOF_DEV_T
                                   ^
../file.c:756:36: warning: 'SIZEOF_DEV_T' is not defined, evaluates to 0 [-Wundef]
# if SIZEOF_STRUCT_STAT_ST_RDEV <= SIZEOF_DEV_T
                                   ^
../file.c:6269:5: warning: 'SIZEOF_DEV_T' is not defined, evaluates to 0 [-Wundef]
#if SIZEOF_DEV_T > SIZEOF_INT
    ^
5 warnings generated.
```

----------------------------------------
Bug #17793: `shorten-64-to-32` error for 32-bit Android due to `struct stat` definition
https://bugs.ruby-lang.org/issues/17793#change-91489

* Author: xtkoba (Tee KOBAYASHI)
* Status: Open
* Priority: Normal
* Backport: 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN
----------------------------------------
[Here is a failure log for armv7a-android from CI.](http://rubyci.s3.amazonaws.com/crossruby/crossruby-master-armv7a-android30/log/20210411T143751Z.fail.html.gz)

This failure is because `struct stat` for 32-bit Android is defined as follows. Note that the member `st_dev` is of type `unsigned long long` (instead of `dev_t`), and `st_mode` is of type `unsigned int` (instead of `mode_t`).

```c
struct stat {
  unsigned long long st_dev;
  unsigned char __pad0[4];
  unsigned long __st_ino;
  unsigned int st_mode;
  nlink_t st_nlink;
  uid_t st_uid;
  gid_t st_gid;
  unsigned long long st_rdev;
  unsigned char __pad3[4];
  long long st_size;
  unsigned long st_blksize;
  unsigned long long st_blocks;
  struct timespec st_atim;
  struct timespec st_mtim;
  struct timespec st_ctim;
  unsigned long long st_ino;
};
```

I personally avoid these errors by passing the following two arguments to `./configure`. I am not 100% sure this results in no other problems.

```
rb_cv_dev_t_convertible=ULL
rb_cv_mode_t_convertible=UINT
```



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