On Thu, Feb 18, 2021 at 05:59:39PM +0100, Peter Zijlstra wrote: > Currently out retpolines consist of 2 symbols, > __x86_indirect_thunk_\reg, which is the compiler target, and > __x86_retpoline_\reg, which is the actual retpoline. Both are > consecutive in code and aligned such that for any one register they > both live in the same cacheline: > > 0000000000000000 <__x86_indirect_thunk_rax>: > 0: ff e0 jmpq *%rax > 2: 90 nop > 3: 90 nop > 4: 90 nop > > 0000000000000005 <__x86_retpoline_rax>: > 5: e8 07 00 00 00 callq 11 <__x86_retpoline_rax+0xc> > a: f3 90 pause > c: 0f ae e8 lfence > f: eb f9 jmp a <__x86_retpoline_rax+0x5> > 11: 48 89 04 24 mov %rax,(%rsp) > 15: c3 retq > 16: 66 2e 0f 1f 84 00 00 00 00 00 nopw %cs:0x0(%rax,%rax,1) > > The thunk is an alternative_2, where one option is a jmp to the > retpoline.
So the reason I originally did that was because objtool could not deal with alternatives with stack ops. But we've recently fixed that.
