lkml.org 
[lkml]   [2020]   [Feb]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH v8 04/12] scs: disable when function graph tracing is enabled
On Wed, Feb 19, 2020 at 3:34 AM Mark Rutland <mark.rutland@arm.com> wrote:
> Fangrui Song has implemented `-fpatchable-function-entry` in LLVM (for
> 10.x onwards), so we can support this when DYNAMIC_FTRACE_WITH_REGS is
> selected.
>
> This can be:
>
> depends on DYNAMIC_FTRACE_WITH_REGS || !FUNCTION_GRAPH_TRACER
>
> ... and we can update the commit message to something like:
>
> | With SCS the return address is taken from the shadow stack and the
> | value in the frame record has no effect. The mcount based graph tracer
> | hooks returns by modifying frame records on the (regular) stack, and
> | thus is not compatible. The patchable-function-entry graph tracer
> | used for DYNAMIC_FTRACE_WITH_REGS modifies the LR before it is saved
> | to the shadow stack, and is compatible.
> |
> | Modifying the mcount based graph tracer to work with SCS would require
> | a mechanism to determine the corresponding slot on the shadow stack
> | (and to pass this through the ftrace infrastructure), and we expect
> | that everyone will eventually move to the patchable-function-entry
> | based graph tracer anyway, so for now let's disable SCS when the
> | mcount-based graph tracer is enabled.
> |
> | SCS and patchable-function-entry are both supported from LLVM 10.x.
>
> Assuming you're happy with that:
>
> Reviewed-by: Mark Rutland <mark.rutland@arm.com>

Great, thanks for pointing that out! This looks good to me, I'll use this in v9.

Sami

\
 
 \ /
  Last update: 2020-02-19 19:02    [W:0.313 / U:0.540 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site