Re: [PATCH] x86/tdx: Do not corrupt frame-pointer in __tdx_hypercall()

[Peter Zijlstra]

On Mon, Jan 30, 2023 at 04:53:54PM +0300, Kirill A. Shutemov wrote:
> If compiled with CONFIG_FRAME_POINTER=y, objtool in not happy that
> __tdx_hypercall() messes up RBP.
> 
>   objtool: __tdx_hypercall+0x7f: return with modified stack frame
> 
> Rework the function to store TDX_HCALL_ flags on stack instead of RBP.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Fixes: c30c4b2555ba ("x86/tdx: Refactor __tdx_hypercall() to allow pass down more arguments")
> Link: https://lore.kernel.org/all/202301290255.buUBs99R-lkp@xxxxxxxxx
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> ---
> 
> The patch is against tip/x86/tdx. tip/sched/core removes
> TDX_HCALL_ISSUE_STI. The trird hunk of the patch is not relevant
> after that.

Right, this should work. But it does leave me wondering, should we
perhaps strive to completely remove the flags thing and move to
__tdx_hypercall() and __tdx_hypercall_ret() or something? That is,
simply have two different functions, one with and one without return
data.

It should be trivial to generate that without actual code duplication.