C++ structure/array initialization - c++

Question

I have a C++ array or structure initialization issue that I have not been able to resolve.
I have a 4-level nested structure. Each level is actually the same 48 bytes wrapped in the structure next level up. The issue is when the structure is initialized and declared as a scalar value, it is correctly initialized with the provided values. However, when it is declared as a single element array, all 48 bytes become zeros, as shown below. Unfortunately the structures are too complicated to be pasted here.
If I define 4 simple structures, one containing another, with the innermost one containing the same 12 unsigned integers, then it is initialized correctly, even if it is declared in an array.
Has anyone experienced similar issues? What am I missing? What compiler flags, options, etc could lead to such a problem? Appreciate any comments and help.
#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include "bls12_381/fq.hpp"
static constexpr embedded_pairing::bls12_381::Fq scalar = {
{{{.std_words = {0x1c7238e5, 0xcf1c38e3, 0x786f0c70, 0x1616ec6e, 0x3a6691ae, 0x21537e29,
0x4d9e82ef, 0xa628f1cb, 0x2e5a7ddf, 0xa68a205b, 0x47085aba, 0xcd91de45}}}}
};
static constexpr embedded_pairing::bls12_381::Fq array[1] = {
{{{{.std_words = {0x1c7238e5, 0xcf1c38e3, 0x786f0c70, 0x1616ec6e, 0x3a6691ae, 0x21537e29,
0x4d9e82ef, 0xa628f1cb, 0x2e5a7ddf, 0xa68a205b, 0x47085aba, 0xcd91de45}}}}}
};
void print_struct(const char *title, const uint8_t *cbuf, int len)
{
printf("\n");
printf("[%s] %d\n", title, len);
for (int i = 0; i < len; i++) {
if (i % 30 == 0 && i != 0)
printf("\n");
else if ((i % 10 == 0 || i % 20 == 0) && i != 0)
printf(" ");
printf("%02X ", cbuf[i]);
}
printf("\n");
}
void run_tests()
{
print_struct("scalar", (const uint8_t *) &scalar, sizeof(scalar));
print_struct("array", (const uint8_t *) &array[0], sizeof(array[0]));
}
[scalar] 48
E5 38 72 1C E3 38 1C CF 70 0C 6F 78 6E EC 16 16 AE 91 66 3A 29 7E 53 21 EF 82 9E 4D CB F1
28 A6 DF 7D 5A 2E 5B 20 8A A6 BA 5A 08 47 45 DE 91 CD
[array] 48
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
I've just narrowed down the example.
The following is a complete and standalone example. I also forgot to mention that the initialization on Linux using g++ 9.3.0, -std=c++17, gets the expected results of all FF's. However, on an embedded device, the inherited structure gets all 0's.
#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
struct Data {
uint32_t words;
};
struct Overlay {
Data val;
};
struct Inherit : Data {
};
static Overlay overlay[1] = {
{{.words = 0xffffffff}}
};
static Inherit inherit[1] = {
{{.words = 0xffffffff}}
};
void print_struct(const char *title, const uint8_t *cbuf, int len)
{
printf("[%s] %d\n", title, len);
for (int i = 0; i < len; i++) {
printf("%02X ", cbuf[i]);
}
printf("\n");
}
int main()
{
print_struct("overlay", (const uint8_t *) &overlay[0], sizeof(overlay[0])); // FF FF FF FF
print_struct("inherit", (const uint8_t *) &inherit[0], sizeof(inherit[0])); // 00 00 00 00 <-- incorrect?
return 0;
}