On 5/11/17 12:31 PM, David Miller wrote:
I haven't done more work on bintuils BPF support because we
need to figure out exactly what to do with relocations. So
I've been trying to spend time thinking about this.
As far as I can tell the 64-bit BPF relocation llvm uses
is used in two situations:
1) 64-bit relocations against data
2) 64-bit relocations against ldimm64 instructions
If this is true it's a very bad decision that has ramifications for us
right now.
One must always explicitly define relocations as being against data or
instruction fields. You cannot use the same relocation for both kinds
of transformations, somehow trying to figure out what to do
"contextually". That doesn't work.
why it doesn't work?
as far as i can see x86 doesn't care where the relo applies.
afaik relocations are divided into absolute, pc relative and pic
relative and it doesn't matter whether they're against .text,
.eh_frame or .debug_* sections.
We have just two so far: absolute 32-bit and absolute 64-bit relocation.
I don't see what we would use pc-relative relo for.
If I remember correctly, the x64 and other cpus use pc-relative for
'call foo' insns since this is how those instructions work.
We don't have such calls yet.
