Messages in this thread | | | From | Sami Tolvanen <> | Date | Fri, 6 Aug 2021 09:20:54 -0700 | Subject | Re: [PATCH v4] kallsyms: strip LTO suffixes from static functions |
| |
On Wed, Jul 7, 2021 at 11:18 AM Nick Desaulniers <ndesaulniers@google.com> 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> > Suggested-by: Nathan Chancellor <nathan@kernel.org> > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> > --- > Changes v3 -> v4: > * Convert this function to use IS_ENABLED rather than provide multiple > definitions based on preprocessor checks. > * Add Nathan's suggested-by. > > Changes v2 -> v3: > * Un-nest preprocessor checks, as per Nathan. > > 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 | 43 ++++++++++++++++++++++++++++++------------- > 1 file changed, 30 insertions(+), 13 deletions(-) > > diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c > index 4067564ec59f..a10dab216f4f 100644 > --- a/kernel/kallsyms.c > +++ b/kernel/kallsyms.c > @@ -171,26 +171,43 @@ 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) > -/* > - * 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(char *s) > { > char *res; > > + /* > + * LLVM appends a suffix for local variables that must be promoted to > + * global scope as part of ThinLTO. foo() becomes > + * foo.llvm.974640843467629774. This can break hooking of static > + * functions with kprobes. > + */ > + if (!IS_ENABLED(CONFIG_LTO_CLANG_THIN)) > + return false; > + > + res = strstr(s, ".llvm."); > + if (res) { > + *res = '\0'; > + return true; > + } > + > + /* > + * LLVM appends a hash to static function names when ThinLTO and CFI > + * are both enabled, i.e. foo() becomes > + * foo$707af9a22804d33c81801f27dcfe489b. This causes confusion and > + * potentially breaks user space tools, so we strip the suffix from > + * expanded symbol names. > + */ > + if (!IS_ENABLED(CONFIG_CFI_CLANG)) > + return false; > + > res = strrchr(s, '$'); > - if (res) > + if (res) { > *res = '\0'; > + return true; > + }
Note that starting with https://reviews.llvm.org/D97484, the hash separator is '.' instead of '$'. It looks like this change will be in Clang 13.
Sami
| |