Re: [PATCH] arm64/module-plts: Consider the special case where plt_max_entries is 0

On Tue, Jul 14, 2020 at 08:48:11AM +0000, 彭浩(Richard) wrote:

On Thu, Jul 09, 2020 at 07:18:01AM +0000,Peng Hao(Richard) wrote:

quoted

On Thu, 9 Jul 2020 at 09:50, Peng Hao(Richard) [off-list ref] wrote:

quoted

quoted

quoted

Apparently, you are hitting a R_AARCH64_JUMP26 or R_AARCH64_CALL26
relocation that operates on a b or bl instruction that is more than
128 megabytes away from its target.

My understanding is that a module that calls functions that are not part of the module will use PLT.
Plt_max_entries =0 May occur if a module does not depend on other module functions.

A PLT slot is allocated for each b or bl instruction that refers to a
symbol that lives in a different section, either of the same module
(e.g., bl in .init calling into .text), of another module, or of the
core kernel.

I don't see how you end up with plt_max_entries in this case, though.

if a module does not depend on other module functions, PLT entries in the module is equal to 0.

quoted

This brings me back to my earlier question: if there are no PLT entries in
the module, then count_plts() will not find any R_AARCH64_JUMP26 or
R_AARCH64_CALL26 relocations that require PLTs and will therefore return 0.
The absence of these relocations means that module_emit_plt_entry() will not
be called by apply_relocate_add(), and so your patch should have no effect.

1.The module in question is the calling function from core kernel.( Ib_core.ko triggered the warning multiple times).
2. There are multiple threads loading IB_core.ko
[   73.388931]  ###cpu=33, name=ib_core, core_plts=0, init_plts=0  
[   73.402102]  #### cpu=33,pid=2297,name=ib_core, module_emit_plt_entry:plt_num_entries=1, plt_max_entries=0 (warning)
[   73.439391]  ###cpu=24, name=ib_core, core_plts=0, init_plts=0  
[   73.448617]  ###cpu=4, name=ib_core, core_plts=0, init_plts=0  
[   73.547535]  ###cpu=221, name=ib_core, core_plts=0, init_plts=0  
[   75.198075]  #### cpu=24,pid=2336,name=ib_core, module_emit_plt_entry:plt_num_entries=1, plt_max_entries=0 (warning)
[   75.489496]  #### cpu=4,pid=2344,name=ib_core, module_emit_plt_entry:plt_num_entries=1, plt_max_entries=0(warning)

I don't understand why count_plts returns 0 when CONFIG_RANDOMIZE_BASE=n for R_AARCH64_JUMP26 and R_AARCH64_CALL26.

3. Set CONFIG_ARM64_MODULE_PLTS=y and restart the server several times without triggering this warning.

Can you provide a means for us to reproduce this failure with an upstream
kernel, please? I really can't tell what's going on from the report. If I
can reproduce the problem locally, then I'm happy to take a look.

Thanks,

Will

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