[Mspgcc-users] Bug Report: Accessing bit-fields in structs

[Jan Hauer]

Hello,

There is a problem with accessing bit fields in structs: It
seems that whenever the first member of a struct is a bitfield
consisting of more than 1 bit a subsequent bitfield in the same struct
is accessed incorrectly (writing seems to work ok, but reading not).
This is true for msp430-gcc 3.3.2 and 3.4.0. It does, however, work
correctly for 3.2.3. I pasted in a simple application isolating the
error.

Compiled under RedHat 9 with:
msp430-gcc -Os -g -mmcu=msp430x149 -o app.elf app.c

Regards,
Jan Hauer


//------------------- code snippet start ---------------------//

typedef struct
{
  unsigned int flag1: 4;
  unsigned int flag2: 1;
} s1_t;

typedef struct {
  volatile unsigned
    flag1: 4,
    flag2: 1;
} __attribute__ ((packed)) s2_t;

typedef struct 
{
  unsigned int flag1: 1;
  unsigned int flag2: 1;
} s3_t;

s1_t s1;
s2_t s2;
s3_t s3;
int test;

int main()
{
  test = 0;
  s1.flag2= 1;
  s2.flag2 = 1;
  s3.flag2 = 1;
  
  if (s1.flag2 == 1)
    test += 1;
  else
    test += 2;

  if (s2.flag2 == 1)
    test += 10;
  else
    test += 20;

  if (s3.flag2 == 1)
    test += 100;
  else
    test += 200;

  // results
  // msp430-gcc 3.2.3: test = 111
  // msp430-gcc 3.3.2: test = 122
  // msp430-gcc 3.4.0: test = 122
}
  
//----------------- code snippet end -------------------//