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bitfields: Implement MS compatible layout

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Bit-fields are layed out differently in visual C, this implements
a compatible mode.  Checked against Visual C/C++ 2016.
Unfortunately the GCC implementation of MS layout (behind
-mms-bitfields) actually is different, and hence not compatible
with MS in all cases :-/
This commit is contained in:
Michael Matz 2016-11-07 19:36:21 +01:00
parent 78c7096162
commit bd69bce20f
1 changed files with 30 additions and 7 deletions
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37
tccgen.c
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@ -3266,7 +3266,7 @@ static void struct_add_offset (Sym *s, int offset)
static void struct_layout(CType *type, AttributeDef *ad)
{
int align, maxalign, offset, c, bit_pos;
int align, maxalign, offset, c, bit_pos, bt, prevbt;
Sym *f;
if (ad->a.aligned)
maxalign = ad->a.aligned;
@ -3275,6 +3275,7 @@ static void struct_layout(CType *type, AttributeDef *ad)
offset = 0;
c = 0;
bit_pos = 0;
prevbt = VT_STRUCT; /* make it never match */
for (f = type->ref->next; f; f = f->next) {
int extra_bytes = 0;
int typealign, bit_size;
@ -3312,7 +3313,7 @@ static void struct_layout(CType *type, AttributeDef *ad)
}
/*if (extra_bytes) c += extra_bytes;
else*/ if (bit_size < 0) {
int addbytes = (bit_pos + 7) >> 3;
int addbytes = pcc ? (bit_pos + 7) >> 3 : 0;
if (type->ref->type.t == TOK_STRUCT) {
c = (c + addbytes + align - 1) & -align;
offset = c;
@ -3328,6 +3329,7 @@ static void struct_layout(CType *type, AttributeDef *ad)
if (align > maxalign)
maxalign = align;
bit_pos = 0;
prevbt = VT_STRUCT;
} else {
/* A bit-field. Layout is more complicated. There are two
options TCC implements: PCC compatible and MS compatible
@ -3347,9 +3349,9 @@ static void struct_layout(CType *type, AttributeDef *ad)
its container (depending on base type) or it's a zero-width
bit-field. Packed non-zero-width bit-fields always are
placed adjacent. */
if (typealign != 1 &&
(bit_pos + bit_size > size * 8 ||
bit_size == 0)) {
if ((typealign != 1 &&
bit_pos + bit_size > size * 8) ||
bit_size == 0) {
c = (c + ((bit_pos + 7) >> 3) + typealign - 1) & -typealign;
offset = c;
bit_pos = 0;
@ -3364,12 +3366,31 @@ static void struct_layout(CType *type, AttributeDef *ad)
maxalign = typealign;
}
} else {
tcc_error("ms bit-field layout not implemented");
bt = f->type.t & VT_BTYPE;
if (
((
bit_pos + bit_size > size * 8) ||
(bit_size == 0 && prevbt == bt) ||
(bit_size > 0 && bt != prevbt))) {
c = (c + typealign - 1) & -typealign;
offset = c;
bit_pos = 0;
/* In MS bitfield mode a bit-field run always uses
at least as many bits as the underlying type. */
c += size;
}
if (bit_size > 0 || prevbt == bt) {
if (align > maxalign)
maxalign = align;
if (typealign > maxalign)
maxalign = typealign;
}
prevbt = bt;
}
f->type.t = (f->type.t & ~(0x3f << VT_STRUCT_SHIFT))
| (bit_pos << VT_STRUCT_SHIFT);
bit_pos += bit_size;
if (bit_pos >= size * 8) {
if (pcc && bit_pos >= size * 8) {
c += size;
bit_pos -= size * 8;
}
@ -3573,6 +3594,8 @@ static void struct_decl(CType *type, AttributeDef *ad, int u)
if (v && bit_size == 0)
tcc_error("zero width for bit-field '%s'",
get_tok_str(v, NULL));
if (tok == TOK_ATTRIBUTE1 || tok == TOK_ATTRIBUTE2)
parse_attribute(&ad1);
}
size = type_size(&type1, &align);
/* Only remember non-default alignment. */