Messages in this thread | | | From | Sami Tolvanen <> | Date | Fri, 1 Oct 2021 13:05:44 -0700 | Subject | Re: [PATCH v5] kallsyms: strip LTO suffixes from static functions |
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On Fri, Oct 1, 2021 at 12:58 PM 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. > > Combine handling of the various schemes by truncating after the first > '.'. Strip off these suffixes so that we can continue to hook such > static functions. Clang releases prior to clang-13 would use '$' > instead of '.' > > Link: https://reviews.llvm.org/rGc6e5c4654bd5045fe22a1a52779e48e2038a404c > Reported-by: KE.LI(Lieke) <like1@oppo.com> > Suggested-by: Fangrui Song <maskray@google.com> > Suggested-by: Nathan Chancellor <nathan@kernel.org> > Suggested-by: Padmanabha Srinivasaiah <treasure4paddy@gmail.com> > Suggested-by: Sami Tolvanen <samitolvanen@google.com> > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> > --- > Changes v4 -> v5: > * Absorb Padmanabha Srinivasaiah's patch from > https://lore.kernel.org/lkml/20210814124224.8551-1-treasure4paddy@gmail.com/. > * Add Padmanabha's Suggested-by tag. > * Rewrite the patch to truncate after first '.', as per Sami's comment > from > https://lore.kernel.org/lkml/CABCJKue5Ay6_+8sibzh5wRh3gPzV1g72gJ9m2ot4E1ezj8bpHA@mail.gmail.com/. > * Add Sami's Suggested-by tag. > * Verify that the '$' delimiter only appears for > thin LTO + CFI + clang <= 12, use __clang_minor__ to check. > * Update comments as per Nathan + Fangrui, add their Suggested-by tags. > * While Nathan + Fangrui did review v4, v5 is too different IMO to carry > those tags forward. > > 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 | 45 ++++++++++++++++++++++++++++++++------------- > 1 file changed, 32 insertions(+), 13 deletions(-) > > diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c > index 0ba87982d017..3e4766204b07 100644 > --- a/kernel/kallsyms.c > +++ b/kernel/kallsyms.c > @@ -164,26 +164,45 @@ 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$707af9a22804d33c81801f27dcfe489b. > - * This causes confusion and potentially breaks user space tools, so we > - * strip the suffix from expanded symbol names. > - */ > -static inline bool cleanup_symbol_name(char *s) > +static bool cleanup_symbol_name(char *s) > { > char *res; > > + if (!IS_ENABLED(CONFIG_LTO_CLANG)) > + return false; > + > + /* > + * LLVM appends various suffixes for local functions and variables that must > + * be promoted to global scope as part of LTO. This can break hooking of > + * static functions with kprobes. '.' is not a valid character in an > + * identifier in C. Suffixes observed: > + * - foo.llvm.[0-9a-f]+ > + * - foo.[0-9a-f]+ > + * - foo.[0-9a-f]+.cfi_jt > + */ > + res = strchr(s, '.'); > + if (res) { > + *res = '\0'; > + return true; > + } > + > + if (!IS_ENABLED(CONFIG_CFI_CLANG) || !IS_ENABLED(CONFIG_LTO_CLANG_THIN) || > + __clang_major__ >= 13) > + return false; > + > + /* > + * Prior to LLVM 13, the following suffixes were observed when thinLTO > + * and CFI are both enabled: > + * - foo$[0-9]+ > + */ > res = strrchr(s, '$'); > - if (res) > + if (res) { > *res = '\0'; > + return true; > + } > > - return res != NULL; > + return false; > } > -#else > -static inline bool cleanup_symbol_name(char *s) { return false; } > -#endif
Thanks for sending the patch, Nick. This looks correct to me.
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Sami
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