Check headers for reallocarray

[FuPeiJiang]

meson's cc.has_function(f) only does a link check (faster)
on Android's bionic libc, reallocarray links, but the headers don't define reallocarray

older malloc.h (on termux):

/**
 * [reallocarray(3)](https://man7.org/linux/man-pages/man3/reallocarray.3.html)
 * resizes allocated memory on the heap.
 *
 * Equivalent to `realloc(__ptr, __item_count * __item_size)` but fails if the
 * multiplication overflows.
 *
 * Returns a pointer (which may be different from `__ptr`) to the resized
 * memory on success and returns a null pointer and sets `errno` on failure
 * (but see the notes for malloc()).
 */
#if __ANDROID_API__ >= 29
__nodiscard void* _Nullable reallocarray(void* _Nullable __ptr, size_t __item_count, size_t __item_size) __BIONIC_ALLOC_SIZE(2, 3) __INTRODUCED_IN(29);
#elif defined(__ANDROID_UNAVAILABLE_SYMBOLS_ARE_WEAK__)
#include <errno.h>
static __inline __nodiscard void* _Nullable reallocarray(void* _Nullable __ptr, size_t __item_count, size_t __item_size) __BIONIC_ALLOC_SIZE(2, 3) {
  size_t __new_size;
  if (__builtin_mul_overflow(__item_count, __item_size, &__new_size)) {
    errno = ENOMEM;
    return NULL;
  }
  return realloc(__ptr, __new_size);
}
#endif

if the header does not define it, (__ANDROID_API__ too low), then use compat.c fallback ?

cc.has_header_symbol(header, f, args: ['-D_GNU_SOURCE'])

symbol check is not a function check, but I don't know how to do a function check
-D_GNU_SOURCE is needed because this is the command used by meson:

... -D_FILE_OFFSET_BITS=64 -O0 -Werror=implicit-function-declaration -std=c11

without -std=c11, it'd work,

#if defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
#include <alloca.h>
...
void *reallocarray (void *, size_t, size_t);
void qsort_r (void *, size_t, size_t, int (*)(const void *, const void *, void *), void *);
#endif

somewhere above:

conf.set('_GNU_SOURCE', true)

defines _GNU_SOURCE, but I found no way of passing conf to cc.has_header_symbol to not have to do

args: ['-D_GNU_SOURCE']

extras:

cc.has_function()

#define reallocarray meson_disable_define_of_reallocarray

#include <limits.h>
#undef reallocarray

#ifdef __cplusplus
extern "C"
#endif
char reallocarray (void);

#if defined __stub_reallocarray || defined __stub___reallocarray
fail fail fail this function is not going to work
#endif

int main(void) {
    return reallocarray ();
}

cc.has_header_symbol()

#include <stdlib.h>
int main(void) {
    /* If it's not defined as a macro, try to use as a symbol */
    #ifndef reallocarray
        reallocarray;
    #endif
    return 0;
}

[rom1v]

Thank you for the PR.

on Android's bionic libc, reallocarray links, but the headers don't define reallocarray

Just for information, does this fix the issue:

diff --git app/src/compat.h app/src/compat.h
index 296d1a9ff..59a2771a2 100644
--- app/src/compat.h
+++ app/src/compat.h
@@ -103,7 +103,7 @@ long nrand48(unsigned short xsubi[3]);
 long jrand48(unsigned short xsubi[3]);
 #endif
 
-#ifndef HAVE_REALLOCARRAY
+#if !defined(HAVE_REALLOCARRAY) || (defined(__ANDROID_API__) && __ANDROID_API__ < 29)
 void *reallocarray(void *ptr, size_t nmemb, size_t size);
 #endif
 

?

EDIT: fixed the condition

[FuPeiJiang]

Just for information, does this fix the issue:

diff --git app/src/compat.h app/src/compat.h
index 296d1a9ff..59a2771a2 100644
--- app/src/compat.h
+++ app/src/compat.h
@@ -103,7 +103,7 @@ long nrand48(unsigned short xsubi[3]);
 long jrand48(unsigned short xsubi[3]);
 #endif
 
-#ifndef HAVE_REALLOCARRAY
+#if !defined(HAVE_REALLOCARRAY) || (defined(__ANDROID_API__) && __ANDROID_API__ < 29)
 void *reallocarray(void *ptr, size_t nmemb, size_t size);
 #endif
 

EDIT: fixed the condition ?

This declares reallocarray when __ANDROID_API__ < 29 (and links to /system/lib64/libc.so)
which may not be desired, if truly targetting __ANDROID_API__ < 29 (older /system/lib64/libc.so doesn't contain reallocarray)

if you want to inline the condition, then:
when __ANDROID_API__ < 29: it should use fallback reallocarray defined in compat.c (declare and define instead of just declare)

diff --git a/app/src/compat.c b/app/src/compat.c
index 785f843..289f54f 100644
--- a/app/src/compat.c
+++ b/app/src/compat.c
@@ -3,7 +3,7 @@
 #include "config.h"
 
 #include <assert.h>
-#ifndef HAVE_REALLOCARRAY
+#if !defined(HAVE_REALLOCARRAY) || (defined(__ANDROID_API__) && __ANDROID_API__ < 29)
 # include <errno.h>
 #endif
 #include <stdlib.h>
@@ -98,7 +98,7 @@ long jrand48(unsigned short xsubi[3]) {
 #endif
 #endif
 
-#ifndef HAVE_REALLOCARRAY
+#if !defined(HAVE_REALLOCARRAY) || (defined(__ANDROID_API__) && __ANDROID_API__ < 29)
 void *reallocarray(void *ptr, size_t nmemb, size_t size) {
     size_t bytes;
     if (__builtin_mul_overflow(nmemb, size, &bytes)) {