On 2024/7/31 9:00, Song Liu wrote: > Hi Masami, > >> On Jul 30, 2024, at 6:03 AM, Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote: >> >> On Mon, 29 Jul 2024 17:54:32 -0700 >> Song Liu <song@xxxxxxxxxx> wrote: >> >>> With CONFIG_LTO_CLANG=y, the compiler may add suffix to function names >>> to avoid duplication. This causes confusion with users of kallsyms. >>> On one hand, users like livepatch are required to match the symbols >>> exactly. On the other hand, users like kprobe would like to match to >>> original function names. >>> >>> Solve this by splitting kallsyms APIs. Specifically, existing APIs now >>> should match the symbols exactly. Add two APIs that matches the full >>> symbol, or only the part without .llvm.suffix. Specifically, the following >>> two APIs are added: >>> >>> 1. kallsyms_lookup_name_or_prefix() >>> 2. kallsyms_on_each_match_symbol_or_prefix() >> >> Since this API only removes the suffix, "match prefix" is a bit confusing. >> (this sounds like matching "foo" with "foo" and "foo_bar", but in reality, >> it only matches "foo" and "foo.llvm.*") >> What about the name below? >> >> kallsyms_lookup_name_without_suffix() >> kallsyms_on_each_match_symbol_without_suffix() > > I am open to name suggestions. I named it as xx or prefix to highlight > that these two APIs will try match full name first, and they only match > the symbol without suffix when there is no full name match. > > Maybe we can call them: > - kallsyms_lookup_name_or_without_suffix() > - kallsyms_on_each_match_symbol_or_without_suffix() > > Again, I am open to any name selections here. Only static functions have suffixes. In my opinion, explicitly marking static might be a little clearer. kallsyms_lookup_static_name() kallsyms_on_each_match_static_symbol() > >> >>> >>> These APIs will be used by kprobe. >> >> No other user need this? > > AFACIT, kprobe is the only use case here. Sami, please correct > me if I missed any users. > > > More thoughts on this: > > I actually hope we don't need these two new APIs, as they are > confusing. Modern compilers can do many things to the code > (inlining, etc.). So when we are tracing a function, we are not > really tracing "function in the source code". Instead, we are > tracing "function in the binary". If a function is inlined, it > will not show up in the binary. If a function is _partially_ > inlined (inlined by some callers, but not by others), it will > show up in the binary, but we won't be tracing it as it appears > in the source code. Therefore, tracing functions by their names > in the source code only works under certain assumptions. And > these assumptions may not hold with modern compilers. Ideally, > I think we cannot promise the user can use name "ping_table" to > trace function "ping_table.llvm.15394922576589127018" > > Does this make sense? > > Thanks, > Song > > > [...] > -- Regards, Zhen Lei
