Messages in this thread | | | Date | Mon, 4 Oct 2021 12:46:40 +0200 | From | Padmanabha Srinivasaiah <> | Subject | Re: [PATCH v5] kallsyms: strip LTO suffixes from static functions |
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On Fri, Oct 01, 2021 at 01:05:44PM -0700, Sami Tolvanen wrote: > 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
Nick, Thanks for absorbing the patch and sharing same. Sami, Thanks for reviewing and yours inputs
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