Using the LLVM backend of BPF, I sometimes get the wrong code to be
generated.
For example, for the following program:
int bpf_prog1(void *ign)
{
volatile unsigned long t = 0x8983984739ull;
return *(unsigned long *)((0xffffffff8fff0002ull) + t);
}
The generated code is
0: 18 01 00 00 39 47 98 83 00 00 00 00 89 00 00 00 r1 =
590618314553ll
2: 7b 1a f8 ff 00 00 00 00 *(u64 *)(r10 - 8) = r1
3: 79 a1 f8 ff 00 00 00 00 r1 = *(u64 *)(r10 - 8)
4: 79 10 02 00 00 00 00 00 r0 = *(u64 *)(r1 + 2)
5: 95 00 00 00 00 00 00 00 exit
The culprit seems to be in the offset check in BPFDAGToDAGISel::SelectAddr()
( and BPFDAGToDAGISel::SelectFIAddr() ).
Currently, the check is done using:
if (isInt<32>(CN->getSExtValue()))
When in fact, the offset is 16-bit, so it should be done using:
if (isInt<16>(CN->getSExtValue()))
Please let me know what you think.
Thanks,
Nadav
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