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Fix bitfields with non-int types and in unions 

The ISO C draft allow only signed/unsigned int and _Bool as base type
for bitfields. TinyCC ever since allowed a wider range of types, but
there were many bugs that shifted values when they shouldn't, etc..
The patch introduces a restriction to the layout of bitfields with
mixed types that makes it incompatible with GCC. In

struct {
  typeA x:1;
  typeB y:1;
};

y is combined with x in the same byte iff typeA is typeB (neglecting
signedness). This is done to avoid alignment issues and exceeding the
width of typeA.
tcc-xref
Daniel Glöckner 2008-09-11 19:18:58 +02:00 committed by grischka
parent 43a34d354a
commit 3783b33508
1 changed files with 28 additions and 8 deletions
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36
tcc.c
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@ -4929,10 +4929,17 @@ int gv(int rc)
/* NOTE: get_reg can modify vstack[] */
if (vtop->type.t & VT_BITFIELD) {
CType type;
bit_pos = (vtop->type.t >> VT_STRUCT_SHIFT) & 0x3f;
bit_size = (vtop->type.t >> (VT_STRUCT_SHIFT + 6)) & 0x3f;
/* remove bit field info to avoid loops */
vtop->type.t &= ~(VT_BITFIELD | (-1 << VT_STRUCT_SHIFT));
/* cast to int to propagate signedness in following ops */
type.t = VT_INT;
if((vtop->type.t & VT_UNSIGNED) ||
(vtop->type.t & VT_BTYPE) == VT_BOOL)
type.t |= VT_UNSIGNED;
gen_cast(&type);
/* generate shifts */
vpushi(32 - (bit_pos + bit_size));
gen_op(TOK_SHL);
@ -6465,7 +6472,7 @@ void vstore(void)
(sbt == VT_INT && dbt == VT_SHORT)) {
/* optimize char/short casts */
delayed_cast = VT_MUSTCAST;
vtop->type.t = ft & VT_TYPE;
vtop->type.t = ft & (VT_TYPE & ~(VT_BITFIELD | (-1 << VT_STRUCT_SHIFT)));
/* XXX: factorize */
if (ft & VT_CONSTANT)
warning("assignment of read-only location");
@ -6522,13 +6529,20 @@ void vstore(void)
vswap();
vrott(3);
if((ft & VT_BTYPE) == VT_BOOL) {
gen_cast(&vtop[-1].type);
vtop[-1].type.t = (vtop[-1].type.t & ~VT_BTYPE) | (VT_BYTE | VT_UNSIGNED);
}
/* duplicate destination */
vdup();
vtop[-1] = vtop[-2];
/* mask and shift source */
vpushi((1 << bit_size) - 1);
gen_op('&');
if((ft & VT_BTYPE) != VT_BOOL) {
vpushi((1 << bit_size) - 1);
gen_op('&');
}
vpushi(bit_pos);
gen_op(TOK_SHL);
/* load destination, mask and or with source */
@ -6724,7 +6738,7 @@ static void parse_attribute(AttributeDef *ad)
static void struct_decl(CType *type, int u)
{
int a, v, size, align, maxalign, c, offset;
int bit_size, bit_pos, bsize, bt, lbit_pos;
int bit_size, bit_pos, bsize, bt, lbit_pos, prevbt;
Sym *s, *ss, *ass, **ps;
AttributeDef ad;
CType type1, btype;
@ -6787,6 +6801,7 @@ static void struct_decl(CType *type, int u)
} else {
maxalign = 1;
ps = &s->next;
prevbt = VT_INT;
bit_pos = 0;
offset = 0;
while (tok != '}') {
@ -6845,11 +6860,13 @@ static void struct_decl(CType *type, int u)
/* XXX: what to do if only padding in a
structure ? */
/* zero size: means to pad */
if (bit_pos > 0)
bit_pos = bsize;
bit_pos = 0;
} else {
/* we do not have enough room ? */
if ((bit_pos + bit_size) > bsize)
/* we do not have enough room ?
did the type change?
is it a union? */
if ((bit_pos + bit_size) > bsize ||
bt != prevbt || a == TOK_UNION)
bit_pos = 0;
lbit_pos = bit_pos;
/* XXX: handle LSB first */
@ -6858,6 +6875,7 @@ static void struct_decl(CType *type, int u)
(bit_size << (VT_STRUCT_SHIFT + 6));
bit_pos += bit_size;
}
prevbt = bt;
} else {
bit_pos = 0;
}
@ -8684,6 +8702,8 @@ static void init_putv(CType *type, Section *sec, unsigned long c,
(bt == VT_INT && bit_size != 32)))
error("initializer element is not computable at load time");
switch(bt) {
case VT_BOOL:
vtop->c.i = (vtop->c.i != 0);
case VT_BYTE:
*(char *)ptr |= (vtop->c.i & bit_mask) << bit_pos;
break;