Re: [PATCH v7 0/2] ARM: Implement MODULE_PLT support in FTRACE

(+ Linus)

On Wed, 3 Feb 2021 at 19:24, Florian Fainelli [off-list ref] wrote:

On 1/27/21 3:09 AM, Alexander A Sverdlin wrote:

quoted

From: Alexander Sverdlin <redacted>

FTRACE's function tracer currently doesn't always work on ARM with
MODULE_PLT option enabled. If the module is loaded too far, FTRACE's
code modifier cannot cope with introduced veneers and turns the
function tracer off globally.

ARM64 already has a solution for the problem, refer to the following
patches:

arm64: ftrace: emit ftrace-mod.o contents through code
arm64: module-plts: factor out PLT generation code for ftrace
arm64: ftrace: fix !CONFIG_ARM64_MODULE_PLTS kernels
arm64: ftrace: fix building without CONFIG_MODULES
arm64: ftrace: add support for far branches to dynamic ftrace
arm64: ftrace: don't validate branch via PLT in ftrace_make_nop()

But the presented ARM variant has just a half of the footprint in terms of
the changed LoCs. It also retains the code validation-before-modification
instead of switching it off.

Ard, Russell should this be sent to the patch tracker?

Apologies for the delay. Unfortunately, I don't have time to review this.

Linus?

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