Wrong ABI: structs with unnamed bit-fields

[ch3root]

The second sizeof in the testcase below gives different results in tis-interpreter and in gcc/clang.

Source code:

#include <stdio.h>

int main()
{
  printf("%zu %zu %zu\n",
    sizeof(struct { char c; int  :0; }),
    sizeof(struct { char c; int  :1; }),
    sizeof(struct { char c; char :1; }));
}

tis-interpreter (21f4c7a) output:

[value] Analyzing a complete application starting at main
[value] Computing initial state
[value] Initial state computed

4 4 2

[value] done for function main

gcc (GCC) 7.0.0 20160627 (experimental):

$ gcc -std=c11 -pedantic -Wall -Wextra -O3 -fsanitize=undefined test.c && ./a.out
4 2 2

clang version 3.9.0 (trunk 271312):

$ clang -std=c11 -Weverything -Wno-padded -O3 -fsanitize=undefined test.c && ./a.out
4 2 2

Relevant rule from amd64 abi -- the last sentence in 3.1.2.:

"Unnamed bit-fields’ types do not affect the alignment of a structure or union."

Not sure what doesn it mean for the first sizeof in the testcase...