jrtc27 added inline comments.
================
Comment at: lldb/source/Host/common/NativeProcessProtocol.cpp:525-526
static const uint8_t g_s390x_opcode[] = {0x00, 0x01};
+ static const uint8_t g_ppc_opcode[] = {0x7f, 0xc0, 0x00, 0x08};
static const uint8_t g_ppc64le_opcode[] = {0x08, 0x00, 0xe0, 0x7f}; // trap
----------------
mgorny wrote:
> mgorny wrote:
> > jrtc27 wrote:
> > > krytarowski wrote:
> > > > jrtc27 wrote:
> > > > > Why are these two different? Should it not always be `trap` ie `tw
> > > > > 31,0,0`? If not that should be explained here. These names also
> > > > > aren't great as it's unclear which ppc64 is using unless you read the
> > > > > code below (I'd expect either ppc and ppc64 or ppc and ppcle as the
> > > > > two "axes", but ppc and ppc64le are on a diagonal in the 2x2 grid).
> > > > On PPC we assume Big-Endian unless specified otherwise, so no need to
> > > > specify ppcbe or ppc64be.
> > > I realise why there is no `be` suffix, that's not what I was asking.
> > > Currently there are four options (though ppcle isn't implemented in
> > > FreeBSD):
> > > | | Big | Little |
> > > | 32 | ppc | ppcle |
> > > | 64 | ppc64 | ppc64le |
> > >
> > > If the difference between the two encodings is solely endianness then
> > > they should be called `g_ppc_opcode` and `g_ppcle_opcode`. If the
> > > difference between the two encodings is solely machine word size then
> > > they should be called `g_ppc_opcode` and g_ppc64_opcode`. But
> > > `g_ppc_opcode` vs g_ppc64le_opcode` has *both* differences in the name,
> > > which tells you nothing about *why* they are different, and thus does not
> > > obviously state which encoding ppc64 uses, if either of them.
> > >
> > > As for the encodings themselves, they obviously differ in endianness, but
> > > there is also a difference in the second/third byte where
> > > `g_ppc_opcode[1]` is `0xc0` but `g_ppc64le_opcode[2]` is `0xe0`. That
> > > does not make sense to me, but if it's there for a reason it needs a
> > > comment.
> > I don't really know what's the difference between the `0xc0` and `0xe0`
> > opcode. Both can be found in various places in LLDB sources. I've copied
> > this one from `source/Target/Platform.cpp`). Maybe `0xc0` works on Big
> > Endian ppc as well, I've copied `0xe0` because it was used by the relevant
> > code before. I'll simplify the code as suggested and try `0xc0`.
> Sorry, I got the two exchanged. I meant I'm going to try `0xe0`.
FWIW 0xc is `tw 30, 0, 0` whereas 0xe is `tw 31, 0, 0` i.e. the canonical
unconditional trap instruction, which `trap` is an alias for.
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D95947/new/
https://reviews.llvm.org/D95947
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