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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <07c221c020bfa0e03566e06e036ff5a923d6a324.1589552055.git.szabolcs.nagy@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: Adhemerval Zanella via Libc-alpha Reply-To: Adhemerval Zanella Errors-To: libc-alpha-bounces@sourceware.org Sender: "Libc-alpha" On 15/05/2020 11:40, Szabolcs Nagy wrote: > RETURN_ADDRESS is used at several places in glibc to mean a valid > code address of the call site, but with pac-ret it has a pointer > authentication code (PAC), so its definition is adjusted. > > strip_pac is omitted if glibc is bulit without pac-ret, but it could s/bulit/built > be added unconditionally (that's just unnecessary operations). > Inline asm is used instead of __builtin_aarch64_xpaclri since that > is an undocumented builtin and not available in all supported gccs. > > Note: such change indicates a problem in the pac-ret design: it > can break code that uses __builtin_return_address and the breakage > is only visible at runtime on a system with pac-ret enabled. It is > not ideal that users need target specific inline asm to fix this up. > For now we can recommend disabling pac-ret where this is a problem, > but gcc might need improvements in this are to make pac-ret usable. > > TODO: __builtin_return_address handling with pac-ret: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94891 LGTM, thanks. Reviewed-by: Adhemerval Zanella > --- > sysdeps/aarch64/sysdep.h | 17 +++++++++++++++++ > 1 file changed, 17 insertions(+) > > diff --git a/sysdeps/aarch64/sysdep.h b/sysdeps/aarch64/sysdep.h > index c51572a690..7a70cf7a2b 100644 > --- a/sysdeps/aarch64/sysdep.h > +++ b/sysdeps/aarch64/sysdep.h > @@ -35,6 +35,23 @@ > > #define PTR_SIZE (1< > +#ifndef __ASSEMBLER__ > +/* Strip pointer authentication code from pointer p. */ > +static inline void * > +strip_pac (void *p) > +{ > + register void *ra asm ("x30") = (p); > + asm ("hint 7 // xpaclri" : "+r"(ra)); > + return ra; Indentation seems off here (tab instead of double space). > +} > + > +/* This is needed when glibc is built with -mbranch-protection=pac-ret. */ > +# ifdef HAVE_AARCH64_PAC_RET > +# undef RETURN_ADDRESS > +# define RETURN_ADDRESS(n) strip_pac (__builtin_return_address (n)) > +# endif > +#endif > + > #ifdef __ASSEMBLER__ > > /* Syntactic details of assembler. */ > Ok.