Messages in this thread | | | Subject | Re: [PATCH v2] kallsyms: strip LTO suffixes from static functions | From | Nathan Chancellor <> | Date | Mon, 28 Jun 2021 12:45:59 -0700 |
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On 6/28/2021 12:05 PM, 'Nick Desaulniers' via Clang Built Linux wrote: > Similar to: > commit 8b8e6b5d3b01 ("kallsyms: strip ThinLTO hashes from static > functions") > > It's very common for compilers to modify the symbol name for static > functions as part of optimizing transformations. That makes hooking > static functions (that weren't inlined or DCE'd) with kprobes difficult. > > LLVM has yet another name mangling scheme used by thin LTO. Strip off > these suffixes so that we can continue to hook such static functions. > > Reported-by: KE.LI(Lieke) <like1@oppo.com> > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> > --- > Changes v1 -> v2: > * Both mangling schemes can occur for thinLTO + CFI, this new scheme can > also occur for thinLTO without CFI. Split cleanup_symbol_name() into > two function calls. > * Drop KE.LI's tested by tag. > * Do not carry Fangrui's Reviewed by tag. > * Drop the inline keyword; it is meaningless. > > kernel/kallsyms.c | 33 +++++++++++++++++++++++++++++---- > 1 file changed, 29 insertions(+), 4 deletions(-) > > diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c > index 4067564ec59f..fbce4a1ec700 100644 > --- a/kernel/kallsyms.c > +++ b/kernel/kallsyms.c > @@ -171,14 +171,30 @@ static unsigned long kallsyms_sym_address(int idx) > return kallsyms_relative_base - 1 - kallsyms_offsets[idx]; > } > > -#if defined(CONFIG_CFI_CLANG) && defined(CONFIG_LTO_CLANG_THIN) > +#ifdef CONFIG_LTO_CLANG_THIN > +/* > + * LLVM appends a suffix for local variables that must be promoted to global > + * scope as part of thin LTO. foo() becomes foo.llvm.974640843467629774. This > + * can break hooking of static functions with kprobes. > + */ > +static bool cleanup_symbol_name_thinlto(char *s) > +{ > + char *res; > + > + res = strstr(s, ".llvm."); > + if (res) > + *res = '\0'; > + > + return res != NULL; > +} > +#ifdef CONFIG_CFI_CLANG > /* > * LLVM appends a hash to static function names when ThinLTO and CFI are > * both enabled, i.e. foo() becomes foo$707af9a22804d33c81801f27dcfe489b. > * This causes confusion and potentially breaks user space tools, so we > * strip the suffix from expanded symbol names. > */ > -static inline bool cleanup_symbol_name(char *s) > +static bool cleanup_symbol_name_thinlto_cfi(char *s) > { > char *res; > > @@ -189,8 +205,17 @@ static inline bool cleanup_symbol_name(char *s) > return res != NULL; > } > #else > -static inline bool cleanup_symbol_name(char *s) { return false; } > -#endif > +static bool cleanup_symbol_name_thinlto_cfi(char *s) { return false; } > +#endif /* CONFIG_CFI_CLANG */ > +#else > +static bool cleanup_symbol_name_thinlto(char *s) { return false; } > +#endif /* CONFIG_LTO_CLANG_THIN */ > + > +static bool cleanup_symbol_name(char *s) > +{ > + return cleanup_symbol_name_thinlto(s) && > + cleanup_symbol_name_thinlto_cfi(s);
Won't this be a build error when CONFIG_LTO_CLANG_THIN=n and CONFIG_CFI_CLANG=n because cleanup_symbol_name_thinlto_cfi() will not be defined? Should the cleanup_symbol_name_thinlto_cfi() stub be in the last else block?
Cheers, Nathan
> +} > > /* Lookup the address for this symbol. Returns 0 if not found. */ > unsigned long kallsyms_lookup_name(const char *name) >
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