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SubjectRe: [PATCH v8 0/3] ARM: Implement MODULE_PLT support in FTRACE
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On 3/30/21 4:40 AM, Alexander A Sverdlin wrote:
> From: Alexander Sverdlin <alexander.sverdlin@nokia.com>
>
> 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.
>
> Changelog:
> v8:
> * Add warn suppress parameter to arm_gen_branch_link()
> v7:
> * rebased
> v6:
> * rebased
> v5:
> * BUILD_BUG_ON() ensures fixed_plts[] always fits one PLT block
> * use "for" loop instead of "while"
> * scripts/recordmcount is filtering reloc types
> v4:
> * Fixed build without CONFIG_FUNCTION_TRACER
> * Reorganized pre-allocated PLTs handling in get_module_plt(),
> now compiler eliminates the whole FTRACE-related handling code
> if ARRAY_SIZE(fixed_plts) == 0
> v3:
> * Only extend struct dyn_arch_ftrace when ARM_MODULE_PLTS is enabled
> v2:
> * As suggested by Steven Rostedt, refrain from tree-wide API modification,
> save module pointer in struct dyn_arch_ftrace instead (PowerPC way)
>
> Alexander Sverdlin (3):
> ARM: PLT: Move struct plt_entries definition to header
> ARM: Add warn suppress parameter to arm_gen_branch_link()
> ARM: ftrace: Add MODULE_PLTS support

Tested-by: Florian Fainelli <f.fainelli@gmail.com>

Thanks a lot!
--
Florian

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