[Tinycc-devel] question about bit-fields

[Didier Barvaux]

Hello all,

I'm trying to build my project with tcc (yesterday's git version). It
succeeds without any required change (cool!), but tests fail :(

I narrowed the problem to bit-fields, and more especially to the length
of some bit-fields. I created a small test program to explain the
problem:

$ cat test.c 

#include <stdint.h>

struct data
{
        unsigned int foo:4;
        unsigned int bar:4;
        uint8_t other;
        uint16_t other2;
};

int main(void)
{
        return sizeof(struct data);
}

$ gcc -Wall -Werror -Wextra -g -O2 -o test_gcc test.c
$ ./test_gcc ; echo $?
4
$ clang -Wall -Werror -Wextra -g -O2 -o test_clang test.c
$ ./test_clang ; echo $?
4
$ tcc -Wall -Werror -Wextra -g -O2 -o test_tcc test.c
$ ./test_tcc ; echo $?
8

Length 4 is expected, but tcc reports 8. Reporting the expected
length is important because the structure defines a network header.

I then tried to replace unsigned-int-based bitfield by an uint8_t-based
bitfield:

$ cat test2.c 

#include <stdint.h>

struct data
{
        uint8_t foo:4;
        uint8_t bar:4;
        uint8_t other;
        uint16_t other2;
};

int main(void)
{
        return sizeof(struct data);
}

$ gcc -Wall -Werror -Wextra -g -O2 -o test2_gcc test2.c
$ ./test2_gcc ; echo $?
4
$ clang -Wall -Werror -Wextra -g -O2 -o test2_clang test2.c
$ ./test2_clang ; echo $?
4
$ tcc -Wall -Werror -Wextra -g -O2 -o test2_tcc test2.c
$ ./test2_tcc ; echo $?
4

Expected result is given by tcc this time. Problem is that I cannot
change the struct's definition from unsigned int to uint8_t.

Is there an option or a declaration to make tcc compute the expected
length for unsigned-int-based bit fields?

For the record, GCC is version 4.5.3, clang is version 3.0, and tcc is
git rev f98c2306a0857ad3f8800f91e0554a27adc7f675.

Regards,
Didier

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