Re: [PATCH] powerpc: Ensure .mem(init|exit).text are within _stext/_etext

Hi,

In our linker script we open code the list of text sections, because
we need to include the __ftr_alt sections, which are arch-specific.

This means we can't use TEXT_TEXT as defined in vmlinux.lds.h, and so
we don't have the MEM_KEEP() logic for memory hotplug sections.

If we build the kernel with the gold linker, and with
CONFIG_MEMORY_HOTPLUG=y, we see that functions marked __meminit can
end up outside of the _stext/_etext range, and also outside of
_sinittext/_einittext, eg:

    c000000000000000 T _stext
    c0000000009e0000 A _etext
    c0000000009e3f18 T hash__vmemmap_create_mapping
    c000000000ca0000 T _sinittext
    c000000000d00844 T _einittext

This causes them to not be recognised as text by is_kernel_text(), and
prevents them being patched by jump_label (and presumably
ftrace/kprobes etc.).

Fix it by adding MEM_KEEP() directives, mirroring what TEXT_TEXT does.

This isn't a problem when CONFIG_MEMORY_HOTPLUG=n, because we use the
standard INIT_TEXT_SECTION() and EXIT_TEXT macros from vmlinux.lds.h.

Thanks Michael, looks good:

Tested-by: Anton Blanchard <redacted>

Anton
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