typedef unsigned int UInt32;
typedef unsigned char UInt8;
struct Data
{
UInt8 data[16];
const UInt8* getData() const
{
return data + 4;
}
};
struct Value {
UInt32 value;
static void update (Value& signal, const Data& source, UInt32 startBit);
};
void Value::update(Value& signal, const Data& source, UInt32 startByte)
{
UInt32& value = signal.value;
const UInt8* data = source.getData();
asm( "lwbrx %0,%1,%2;\n":"=r"(value): "r"(data), "r"(startByte), "m" (*(data
+ startByte)) );
}
generated for gcc-4.2.4 on powerpc:
00000000 <_ZN5Value6updateERS_RK4Dataj>:
0: 38 04 00 04 addi r0,r4,4
4: 7c 80 2c 2c lwbrx r4,0,r5
8: 90 83 00 00 stw r4,0(r3)
c: 4e 80 00 20 blr
the correct version without -funroll-loops reads:
00000000 <_ZN5Value6updateERS_RK4Dataj>:
0: 38 84 00 04 addi r4,r4,4
4: 7c 84 2c 2c lwbrx r4,r4,r5
8: 90 83 00 00 stw r4,0(r3)
c: 4e 80 00 20 blr
lwbrx sums the contents of r4 and r5 and accesses this address, swaps it's
value and stores it again in r4. The incorrect version accesses an invalid
address, which leads to a segmentation fault.
this is corrected at least with gcc-4.3.1, there i couldn't reproduce the
behaviour.
--
Summary: [4.2] -funroll-loops destroys inline asm code von
powerpc
Product: gcc
Version: 4.2.4
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: inline-asm
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: rbuergel at web dot de
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37562
