Messages in this thread | | | Subject | Re: [PATCH v2 1/1] x86/tdx: Add __tdcall() and __tdvmcall() helper functions | From | Dave Hansen <> | Date | Thu, 22 Apr 2021 18:21:07 -0700 |
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On 4/22/21 6:09 PM, Kuppuswamy, Sathyanarayanan wrote: > But let me try to explain it here. What I meant by complication is, > for in/out instruction, we use alternative_io() to substitute in/out > instructions with tdg_in()/tdg_out() assembly calls. So we have to ensure > that we don't corrupt registers or stack from the substituted instructions > > If you check the implementation of tdg_in()/tdg_out(), you will notice > that we have added code to preserve the caller registers. So, if we use > C wrapper for this use case, there is a chance that it might mess > the caller registers or stack. > > alternative_io("in" #bwl " %w2, %" #bw "0", \ > "call tdg_in" #bwl, X86_FEATURE_TDX_GUEST, \ > "=a"(value), "d"(port))
Are you saying that calling C functions from inline assembly might corrupt the stack or registers? Are you suggesting that you simply can't call C functions from inline assembly? Or, that you can't express the register clobbers of a function call in inline assembly?
You might want to check around the kernel to see how other folks do it.
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