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    SubjectRe: [PATCH v8 0/3] ARM: Implement MODULE_PLT support in FTRACE
    Date
    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)

    FWIW, ftracetest did not pick up new failures (nor were new tests fixed)
    with this patch series.
    --
    Florian

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