Re: .exit.text section in vmlinux

On Fri, 30 Jun 2006, Magnus Damm wrote:

Hi guys,

I understand why ".exit.text" is present in the case of modules, but I
can't get my head around why it is included in the vmlinux file.
Functions like the ones below puzzle me:

kernel/configs.c: static void __exit ikconfig_cleanup(void)
drivers/net/ne2k-pci.c: static void __exit ne2k_pci_cleanup(void)
drivers/net/ne2k-pci.c: static void __devexit ne2k_pci_remove_one
(struct pci_dev *pdev)

I can see how the last "__devexit" function might be called during
some hotplug event, but are the two "__exit" functions ever going to
be called from the kernel? Since my kernel is configured without
CONFIG_HOTPLUG both both "__exit" and "__devexit" end up in the
".exit.text" section.

The linker script arch/i386/kernel/vmlinux.lds.S mentions the following:

/* .exit.text is discard at runtime, not link time, to deal with references
from .altinstructions and .eh_frame */

.altinstructions is for alternatives code (code that is rewritten at runtime based on some factor such as UP-vs-SMP). .eh_frame has call framing information used for unwinding. I think it's copied into the vsyscall page (not entirely familiar with this mechanism though).

The text above seems to answer my question, but I cannot say I fully
understand the comment. I'd appreciate if someone could explain a bit
more if possible.

Ok, so the section should be discarded at runtime. Sounds ok. But
where in the code is this section discarded? -ENOSYS?

When you see "Freeing unused kernel memory", the memory between __init_begin and __init_end (as marked in vmlinux.ld.S) is released. See arch-specific mm/init.c.

Thanks,

/ magnus

Thanks,
Chase
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