Re: [PATCH v2 3/3] tracing/kprobes: Use APIs that matches symbols without .XXX suffix

On Aug 8, 2024, at 2:48 AM, Petr Mladek [off-list ref] wrote:

On Wed 2024-08-07 19:46:31, Song Liu wrote:

quoted

quoted

On Aug 7, 2024, at 7:58 AM, zhang warden [off-list ref] wrote:

quoted

In my GCC built, we have suffixes like ".constprop.0", ".part.0", ".isra.0", 
and ".isra.0.cold".

A fresher's eye, I met sometime when try to build a livepatch module and found some mistake caused by ".constprop.0" ".part.0" which is generated by GCC.

These section with such suffixes is special and sometime the symbol st_value is quite different. What is these kind of section (or symbol) use for?

IIUC, constprop means const propagation. For example, function 
"foo(int a, int b)" that is called as "foo(a, 10)" will be come 
"foo(int a)" with a hard-coded b = 10 inside. 

.part.0 is part of the function, as the other part is inlined in 
the caller.

Hmm, we should not remove the suffixes like .constprop*, .part*,
.isra*. They implement a special optimized variant of the function.
It is not longer the original full-featured one.

This is a difference against adding a suffix for a static function.
Such a symbol implements the original full-featured function.

Allow tracing without .llvm.<hash> suffixes may target a different 
function with same name, i.e. func_a.llvm.1 vs. func_a.llvm.2. We
can probably detect and report this in the kernel. However, I would 
rather we just disallow tracing without suffixes. I think Masami
also agrees with this. 

Thanks,
Song