Messages in this thread | | | From | Fāng-ruì Sòng <> | Date | Wed, 7 Jul 2021 11:59:55 -0700 | Subject | Re: [PATCH v4] kallsyms: strip LTO suffixes from static functions |
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On Wed, Jul 7, 2021 at 11:34 AM Nathan Chancellor <nathan@kernel.org> wrote: > > On 7/7/2021 11:18 AM, Nick Desaulniers 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> > > Code looks fine, small comment about a comment below. > > Reviewed-by: Nathan Chancellor <nathan@kernel.org> > > > --- > > 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 > > This says local variables but the example uses a function? Is that correct?
local functions/variables.
Both functions and variables can have a .llvm.[0-9]+ suffix.
Aside from this, the updated description looks good to me
Reviewed-by: Fangrui Song <maskray@google.com>
> > + * 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; > > + } > > > > - return res != NULL; > > + return false; > > } > > -#else > > -static inline bool cleanup_symbol_name(char *s) { return false; } > > -#endif > > > > /* Lookup the address for this symbol. Returns 0 if not found. */ > > unsigned long kallsyms_lookup_name(const char *name) > >
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