Re: [cfe-users] RFC v2: Re: cacheflush.2
Hi Michael, On 12/11/20 9:15 AM, Michael Kerrisk (man-pages) wrote: > i Alex, > > On 12/10/20 9:56 PM, Alejandro Colomar (man-pages) wrote: >> Hi all, >> >> v2: >> >> [ >> NOTES >>Unless you need the finer grained control that this system >>call provides, you probably want to use the GCC built-in >>function __builtin___clear_cache(), which provides a more >>portable interface: >> >>void __builtin___clear_cache(void *begin, void *end); >> ] > > This seems a reasonable text to me, but I think it would be helpful > to say a little more precisely what kind of portability we are > talking about here. Sure. > > Greater ortability across Linux architectures? Greater portability > across platforms supported by GCC (including non-Linux) platforms? > Something else? '... which provides a portable interface across platforms supported by GCC:' sounds good. Maybe GCC devs have something more to add. Thanks, Alex > > Thanks, > > Michael > > -- Alejandro Colomar Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/ http://www.alejandro-colomar.es ___ cfe-users mailing list cfe-users@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-users
[cfe-users] RFC v2: Re: cacheflush.2
Hi all, v2: [ NOTES Unless you need the finer grained control that this system call provides, you probably want to use the GCC built-in function __builtin___clear_cache(), which provides a more portable interface: void __builtin___clear_cache(void *begin, void *end); ] If you like it, I'll send the patch. BTW, I'll also have a look and document the different prototypes for cacheflush(2). Thanks, Alex On 12/10/20 8:20 PM, Heinrich Schuchardt wrote: > On 12/10/20 7:17 PM, Dave Martin wrote: >> On Wed, Dec 09, 2020 at 07:34:09PM +0100, Alejandro Colomar >> (man-pages) wrote: >>> Hi Heinrich & Michael, >>> >>> What about the following?: >>> >>> [ >>> NOTES >>> GCC provides a similar function, which may be useful on archi‐ >>> tectures that lack this system call: >>> >>> void __builtin___clear_cache(void *begin, void *end); >>> ] >>> >>> Cheers, >>> >>> Alex >> >> Maybe we should discourage people from calling the cacheflush syscall? >> >> I think that people shouldn't be using the syscall unless they really >> need the finer grained control it provides, and are prepared to take a >> hit to portability. >> >> (On arches where userspace is allowed to do cache flushing directly, >> __builtin___clear_cache() should transparently do the right thing, with >> no syscall overhead -- if not, that's probably a bug in the toolchain or >> compiler support library.) > > What the compiler builtin does depends on the architecture (e.g. nothing > for x86, cacheflush() for MIPS, a private syscall (0xf0002) on ARM, > assembly code on ARM64, ...) and on the the operating system (Linux, > BSD, OS X). For portable code the builtin is really the best choice. > > Best regards > > Heinrich > >> >> [...] >> >> Cheers >> ---Dave >> > -- Alejandro Colomar Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/ http://www.alejandro-colomar.es ___ cfe-users mailing list cfe-users@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-users
Re: [cfe-users] cacheflush.2
Hi Heinrich, It looks like a bug (or at least an undocumented divergence from GCC) in Clang/LLVM. Or I couldn't find the documentation for it. Clang uses 'char *': https://github.com/llvm/llvm-project/blob/7faf62a80bfc3a9dfe34133681fcc31f8e8d658b/clang/include/clang/Basic/Builtins.def#L583 GCC uses 'void *': https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html I CCd Clang and GCC lists; maybe they know about that divergence. Cheers, Alex On 12/9/20 7:48 PM, Heinrich Schuchardt wrote: > On 12/9/20 7:34 PM, Alejandro Colomar (man-pages) wrote: >> Hi Heinrich & Michael, >> >> What about the following?: >> >> [ >> NOTES >> GCC provides a similar function, which may be useful on archi‐ >> tectures that lack this system call: >> >> void __builtin___clear_cache(void *begin, void *end); >> ] > > I just checked building with Clang/LLVM. There the arguments are of type > (char *). See the following error output: > > +arch/sandbox/cpu/cache.c:19:26: error: passing 'uint8_t *' (aka > 'unsigned char *') to parameter of type 'char *' converts between > pointers to integer types with different sign [-Werror,-Wpointer-sign] > + __builtin___clear_cache(state->ram_buf, > + ^~ > +arch/sandbox/cpu/cache.c:20:12: error: passing 'uint8_t *' (aka > 'unsigned char *') to parameter of type 'char *' converts between > pointers to integer types with different sign [-Werror,-Wpointer-sign] > + state->ram_buf + state->ram_size); > + ^~~~ > > Best regards > > Heinrich > >> >> Cheers, >> >> Alex >> >> On 12/9/20 7:04 PM, Heinrich Schuchardt wrote: >>> Hello Michael, >>> >>> function cacheflush() does not exist on many architectures. >>> >>> It would have saved me a lot of time if the man-page had referenced >>> GCC's >>> >>> void __builtin___clear_cache(void *begin, void *end) >>> >>> Maybe you can add it to NOTES. >>> >>> Best regards >>> >>> heirnich >> > -- Alejandro Colomar Linux man-pages comaintainer; http://www.kernel.org/doc/man-pages/ http://www.alejandro-colomar.es ___ cfe-users mailing list cfe-users@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-users
Re: [cfe-users] cacheflush.2
It looks like GCC recently moved from 'char *' to 'void *'. This SO question[1] (4 years ago) quotes the GCC docs and they had 'char *'. Maybe Clang hasn't noticed the change. I'll report a bug. [1]: https://stackoverflow.com/q/35741814/6872717 On 12/9/20 8:15 PM, Alejandro Colomar (man-pages) wrote: > Hi Heinrich, > > It looks like a bug (or at least an undocumented divergence from GCC) in > Clang/LLVM. Or I couldn't find the documentation for it. > > Clang uses 'char *': > https://github.com/llvm/llvm-project/blob/7faf62a80bfc3a9dfe34133681fcc31f8e8d658b/clang/include/clang/Basic/Builtins.def#L583 > > GCC uses 'void *': > https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html > > I CCd Clang and GCC lists; maybe they know about that divergence. > > Cheers, > > Alex > > On 12/9/20 7:48 PM, Heinrich Schuchardt wrote: >> On 12/9/20 7:34 PM, Alejandro Colomar (man-pages) wrote: >>> Hi Heinrich & Michael, >>> >>> What about the following?: >>> >>> [ >>> NOTES >>> GCC provides a similar function, which may be useful on archi‐ >>> tectures that lack this system call: >>> >>> void __builtin___clear_cache(void *begin, void *end); >>> ] >> >> I just checked building with Clang/LLVM. There the arguments are of type >> (char *). See the following error output: >> >> +arch/sandbox/cpu/cache.c:19:26: error: passing 'uint8_t *' (aka >> 'unsigned char *') to parameter of type 'char *' converts between >> pointers to integer types with different sign [-Werror,-Wpointer-sign] >> + __builtin___clear_cache(state->ram_buf, >> + ^~ >> +arch/sandbox/cpu/cache.c:20:12: error: passing 'uint8_t *' (aka >> 'unsigned char *') to parameter of type 'char *' converts between >> pointers to integer types with different sign [-Werror,-Wpointer-sign] >> + state->ram_buf + state->ram_size); >> + ^~~~ >> >> Best regards >> >> Heinrich >> >>> >>> Cheers, >>> >>> Alex >>> >>> On 12/9/20 7:04 PM, Heinrich Schuchardt wrote: Hello Michael, function cacheflush() does not exist on many architectures. It would have saved me a lot of time if the man-page had referenced GCC's void __builtin___clear_cache(void *begin, void *end) Maybe you can add it to NOTES. Best regards heirnich >>> >> > -- Alejandro Colomar Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/ http://www.alejandro-colomar.es ___ cfe-users mailing list cfe-users@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-users
[cfe-users] RFC v3: Re: cacheflush.2
Hi all, Please review this text: [ NOTES Unless you need the finer grained control that this system call provides, you probably want to use the GCC built-in function __builtin___clear_cache(), which provides a more portable interface: void __builtin___clear_cache(void *begin, void *end); On platforms that don't require instruction cache flushes, __builtin___clear_cache() has no effect. Note: On some GCC-compatible compilers, such as clang, the prototype for this function uses char * instead of void *. ] Thanks, Alex On 12/11/20 7:02 PM, Alejandro Colomar (man-pages) wrote: > Hi Michael, > > On 12/11/20 9:15 AM, Michael Kerrisk (man-pages) wrote: >> i Alex, >> >> On 12/10/20 9:56 PM, Alejandro Colomar (man-pages) wrote: >>> Hi all, >>> >>> v2: >>> >>> [ >>> NOTES >>>Unless you need the finer grained control that this system >>>call provides, you probably want to use the GCC built-in >>>function __builtin___clear_cache(), which provides a more >>>portable interface: >>> >>>void __builtin___clear_cache(void *begin, void *end); >>> ] >> >> This seems a reasonable text to me, but I think it would be helpful >> to say a little more precisely what kind of portability we are >> talking about here. > Sure. > >> >> Greater ortability across Linux architectures? Greater portability >> across platforms supported by GCC (including non-Linux) platforms? >> Something else? > > '... which provides a portable interface across platforms supported by > GCC:' sounds good. > > Maybe GCC devs have something more to add. > > Thanks, > > Alex > >> >> Thanks, >> >> Michael >> >> > -- Alejandro Colomar Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/ http://www.alejandro-colomar.es ___ cfe-users mailing list cfe-users@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-users
[cfe-users] RFC v4: Re: cacheflush.2
I forgot to add a junk to the text. v4: NOTES Unless you need the finer grained control that this system call provides, you probably want to use the GCC built-in function __builtin___clear_cache(), which provides a portable interface across platforms supported by GCC and compatible compilers: //Maybe 'and compatible compilers' is redundant and I should remove it? void __builtin___clear_cache(void *begin, void *end); On platforms that don't require instruction cache flushes, __builtin___clear_cache() has no effect. Note: On some GCC-compatible compilers, such as clang, the prototype for this function uses char * instead of void *. On 12/11/20 7:22 PM, Alejandro Colomar (man-pages) wrote: > Hi all, > > Please review this text: > > [ > NOTES >Unless you need the finer grained control that this system >call provides, you probably want to use the GCC built-in >function __builtin___clear_cache(), which provides a more >portable interface: > >void __builtin___clear_cache(void *begin, void *end); > >On platforms that don't require instruction cache flushes, >__builtin___clear_cache() has no effect. > >Note: On some GCC-compatible compilers, such as clang, the >prototype for this function uses char * instead of void *. > ] > > Thanks, > > Alex > > On 12/11/20 7:02 PM, Alejandro Colomar (man-pages) wrote: >> Hi Michael, >> >> On 12/11/20 9:15 AM, Michael Kerrisk (man-pages) wrote: >>> i Alex, >>> >>> On 12/10/20 9:56 PM, Alejandro Colomar (man-pages) wrote: Hi all, v2: [ NOTES Unless you need the finer grained control that this system call provides, you probably want to use the GCC built-in function __builtin___clear_cache(), which provides a more portable interface: void __builtin___clear_cache(void *begin, void *end); ] >>> >>> This seems a reasonable text to me, but I think it would be helpful >>> to say a little more precisely what kind of portability we are >>> talking about here. >> Sure. >> >>> >>> Greater ortability across Linux architectures? Greater portability >>> across platforms supported by GCC (including non-Linux) platforms? >>> Something else? >> >> '... which provides a portable interface across platforms supported by >> GCC:' sounds good. >> >> Maybe GCC devs have something more to add. > >> >> Thanks, >> >> Alex >> >>> >>> Thanks, >>> >>> Michael >>> >>> >> > -- Alejandro Colomar Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/ http://www.alejandro-colomar.es ___ cfe-users mailing list cfe-users@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-users
Re: [cfe-users] cacheflush.2
Hello Martin, Thanks for the correction! Then the prototypes that changes from 'char *' to 'void *' in r269082 were not exposed to the user, right? I guess then those are just internal implementation where GCC did use 'char *'. Where is the actual prototype exposed to the user declared? Thanks, Alex P.S.: Michael, wait for a patch revision (v6). On 12/14/20 10:13 PM, Martin Sebor wrote: > On 12/11/20 11:14 AM, Alejandro Colomar (man-pages) via Gcc wrote: >> It looks like GCC recently moved from 'char *' to 'void *'. >> This SO question[1] (4 years ago) quotes the GCC docs >> and they had 'char *'. > > __builtin___clear_cache in GCC has always been declared to take > void*. The signature in the manual was recently corrected to match > the implementation, i.e., from char* to void*, in r269082. > > Martin > >> Maybe Clang hasn't noticed the change. >> I'll report a bug. >> >> [1]: https://stackoverflow.com/q/35741814/6872717 >> >> On 12/9/20 8:15 PM, Alejandro Colomar (man-pages) wrote: >>> Hi Heinrich, >>> >>> It looks like a bug (or at least an undocumented divergence from GCC) in >>> Clang/LLVM. Or I couldn't find the documentation for it. >>> >>> Clang uses 'char *': >>> https://github.com/llvm/llvm-project/blob/7faf62a80bfc3a9dfe34133681fcc31f8e8d658b/clang/include/clang/Basic/Builtins.def#L583 >>> >>> >>> GCC uses 'void *': >>> https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html >>> >>> I CCd Clang and GCC lists; maybe they know about that divergence. >>> >>> Cheers, >>> >>> Alex >>> >>> On 12/9/20 7:48 PM, Heinrich Schuchardt wrote: On 12/9/20 7:34 PM, Alejandro Colomar (man-pages) wrote: > Hi Heinrich & Michael, > > What about the following?: > > [ > NOTES > GCC provides a similar function, which may be useful on > archi‐ > tectures that lack this system call: > > void __builtin___clear_cache(void *begin, void *end); > ] I just checked building with Clang/LLVM. There the arguments are of type (char *). See the following error output: +arch/sandbox/cpu/cache.c:19:26: error: passing 'uint8_t *' (aka 'unsigned char *') to parameter of type 'char *' converts between pointers to integer types with different sign [-Werror,-Wpointer-sign] + __builtin___clear_cache(state->ram_buf, + ^~ +arch/sandbox/cpu/cache.c:20:12: error: passing 'uint8_t *' (aka 'unsigned char *') to parameter of type 'char *' converts between pointers to integer types with different sign [-Werror,-Wpointer-sign] + state->ram_buf + state->ram_size); + ^~~~ Best regards Heinrich > > Cheers, > > Alex > > On 12/9/20 7:04 PM, Heinrich Schuchardt wrote: >> Hello Michael, >> >> function cacheflush() does not exist on many architectures. >> >> It would have saved me a lot of time if the man-page had referenced >> GCC's >> >> void __builtin___clear_cache(void *begin, void *end) >> >> Maybe you can add it to NOTES. >> >> Best regards >> >> heirnich > >>> >> > -- Alejandro Colomar Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/ http://www.alejandro-colomar.es ___ cfe-users mailing list cfe-users@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-users
[cfe-users] Ping: cacheflush.2
Hi Martin, I sent you an email, but I received a "delivery failure". If you're reading this from a list, could you answer, please? Thanks, Alex On 12/14/20 11:34 PM, Alejandro Colomar (man-pages) wrote: > Hello Martin, > > Thanks for the correction! > Then the prototypes that changes from 'char *' to 'void *' in r269082 > were not exposed to the user, right? > I guess then those are just internal implementation where GCC did use > 'char *'. > > Where is the actual prototype exposed to the user declared? > > Thanks, > > Alex > > P.S.: Michael, wait for a patch revision (v6). > > On 12/14/20 10:13 PM, Martin Sebor wrote: >> On 12/11/20 11:14 AM, Alejandro Colomar (man-pages) via Gcc wrote: >>> It looks like GCC recently moved from 'char *' to 'void *'. >>> This SO question[1] (4 years ago) quotes the GCC docs >>> and they had 'char *'. >> >> __builtin___clear_cache in GCC has always been declared to take >> void*. The signature in the manual was recently corrected to match >> the implementation, i.e., from char* to void*, in r269082. >> >> Martin >> >>> Maybe Clang hasn't noticed the change. >>> I'll report a bug. >>> >>> [1]: https://stackoverflow.com/q/35741814/6872717 >>> >>> On 12/9/20 8:15 PM, Alejandro Colomar (man-pages) wrote: Hi Heinrich, It looks like a bug (or at least an undocumented divergence from GCC) in Clang/LLVM. Or I couldn't find the documentation for it. Clang uses 'char *': https://github.com/llvm/llvm-project/blob/7faf62a80bfc3a9dfe34133681fcc31f8e8d658b/clang/include/clang/Basic/Builtins.def#L583 GCC uses 'void *': https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html I CCd Clang and GCC lists; maybe they know about that divergence. Cheers, Alex On 12/9/20 7:48 PM, Heinrich Schuchardt wrote: > On 12/9/20 7:34 PM, Alejandro Colomar (man-pages) wrote: >> Hi Heinrich & Michael, >> >> What about the following?: >> >> [ >> NOTES >> GCC provides a similar function, which may be useful on >> archi‐ >> tectures that lack this system call: >> >> void __builtin___clear_cache(void *begin, void *end); >> ] > > I just checked building with Clang/LLVM. There the arguments are of > type > (char *). See the following error output: > > +arch/sandbox/cpu/cache.c:19:26: error: passing 'uint8_t *' (aka > 'unsigned char *') to parameter of type 'char *' converts between > pointers to integer types with different sign [-Werror,-Wpointer-sign] > + __builtin___clear_cache(state->ram_buf, > + ^~ > +arch/sandbox/cpu/cache.c:20:12: error: passing 'uint8_t *' (aka > 'unsigned char *') to parameter of type 'char *' converts between > pointers to integer types with different sign [-Werror,-Wpointer-sign] > + state->ram_buf + state->ram_size); > + ^~~~ > > Best regards > > Heinrich > >> >> Cheers, >> >> Alex >> >> On 12/9/20 7:04 PM, Heinrich Schuchardt wrote: >>> Hello Michael, >>> >>> function cacheflush() does not exist on many architectures. >>> >>> It would have saved me a lot of time if the man-page had referenced >>> GCC's >>> >>> void __builtin___clear_cache(void *begin, void *end) >>> >>> Maybe you can add it to NOTES. >>> >>> Best regards >>> >>> heirnich >> > >>> >> > -- Alejandro Colomar Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/ http://www.alejandro-colomar.es/ ___ cfe-users mailing list cfe-users@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-users
Re: [cfe-users] Ping: cacheflush.2
Hi Martin, Thanks! It's good to learn some GCC internal details :) Cheers, Alex On 12/18/20 5:51 PM, Martin Sebor wrote: > On 12/18/20 3:42 AM, Alejandro Colomar (man-pages) wrote: >> Hi Martin, >> >> I sent you an email, but I received a "delivery failure". >> If you're reading this from a list, could you answer, please? >> >> Thanks, >> >> Alex >> >> On 12/14/20 11:34 PM, Alejandro Colomar (man-pages) wrote: >>> Hello Martin, >>> >>> Thanks for the correction! >>> Then the prototypes that changes from 'char *' to 'void *' in r269082 >>> were not exposed to the user, right? >>> I guess then those are just internal implementation where GCC did use >>> 'char *'. > > __builtin___clear_cache was added to GCC in r126535 (the __builtin_ > prefix is added by the macro): > > +DEF_EXT_LIB_BUILTIN (BUILT_IN_CLEAR_CACHE, "__clear_cache", > BT_FN_VOID_PTR_PTR, ATTR_NOTHROW_LIST) > > The BT_FN_VOID_PTR_PTR macro describes its signature as returning > void and taking two void pointer arguments. AFAIK, this has never > changed. Contrary to that, the manual entry for the built-in added > in the same revision documented it as taking two char*. That was > corrected to void* in r269082 to match. > > There's a GCC internal declaration of __clear_cache (apparently > provided in libgcc for VxWorks). It was added in r264479 and > it also used char*. This was also changed to void* in r269082 > to match the built-in. Looks like this __clear_cache has just > been removed from libgcc in GCC 11: > https://gcc.gnu.org/pipermail/gcc-cvs/2020-December/338478.html > >>> >>> Where is the actual prototype exposed to the user declared? > > Built-in functions are declared implicitly by GCC. They have no > explicit declarations like user-defined functions. The implicit > internal "declarations" are specified in the GCC internal file > gcc/builtins.def, where they are hidden behind layers of macros. > For example, on the GCC 10 branch, the declaration for > __builtin___clear_cache is here: > > https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/builtins.def;h=fa8b0641ab13b36f983c591a7020f6b432e5fb3d;hb=refs/heads/releases/gcc-10#l837 > > > Martin > >>> >>> Thanks, >>> >>> Alex >>> >>> P.S.: Michael, wait for a patch revision (v6). >>> >>> On 12/14/20 10:13 PM, Martin Sebor wrote: On 12/11/20 11:14 AM, Alejandro Colomar (man-pages) via Gcc wrote: > It looks like GCC recently moved from 'char *' to 'void *'. > This SO question[1] (4 years ago) quotes the GCC docs > and they had 'char *'. __builtin___clear_cache in GCC has always been declared to take void*. The signature in the manual was recently corrected to match the implementation, i.e., from char* to void*, in r269082. Martin > Maybe Clang hasn't noticed the change. > I'll report a bug. > > [1]: https://stackoverflow.com/q/35741814/6872717 > > On 12/9/20 8:15 PM, Alejandro Colomar (man-pages) wrote: >> Hi Heinrich, >> >> It looks like a bug (or at least an undocumented divergence from >> GCC) in >> Clang/LLVM. Or I couldn't find the documentation for it. >> >> Clang uses 'char *': >> https://github.com/llvm/llvm-project/blob/7faf62a80bfc3a9dfe34133681fcc31f8e8d658b/clang/include/clang/Basic/Builtins.def#L583 >> >> >> >> GCC uses 'void *': >> https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html >> >> I CCd Clang and GCC lists; maybe they know about that divergence. >> >> Cheers, >> >> Alex >> >> On 12/9/20 7:48 PM, Heinrich Schuchardt wrote: >>> On 12/9/20 7:34 PM, Alejandro Colomar (man-pages) wrote: Hi Heinrich & Michael, What about the following?: [ NOTES GCC provides a similar function, which may be useful on archi‐ tectures that lack this system call: void __builtin___clear_cache(void *begin, void *end); ] >>> >>> I just checked building with Clang/LLVM. There the arguments are of >>> type >>> (char *). See the following error output: >>> >>> +arch/sandbox/cpu/cache.c:19:26: error: passing 'uint8_t *' (aka >>> 'unsigned char *') to parameter of type 'char *' converts between >>> pointers to integer types with different sign >>> [-Werror,-Wpointer-sign] >>> + __builtin___clear_cache(state->ram_buf, >>> + ^~ >>> +arch/sandbox/cpu/cache.c:20:12: error: passing 'uint8_t *' (aka >>> 'unsigned char *') to parameter of type 'char *' converts between >>> pointers to integer types with different sign >>> [-Werror,-Wpointer-sign] >>> + state->ram_buf + state->ram_size); >>> + ^~~~ >>> >>> Best regards >>> >>> Heinrich >>> Cheers
[cfe-users] Ping: [PATCH v6] cacheflush.2: Document __builtin___clear_cache() as a more portable alternative
Ping On 12/15/20 2:30 PM, Alejandro Colomar wrote: > Reported-by: Heinrich Schuchardt > Signed-off-by: Alejandro Colomar > Cc: Martin Sebor > Cc: Dave Martin > --- > > v6: > - GCC has always exposed 'void *', as Martin Sebor noted. > It's Clang (and maybe others) that (following GCC's docs) > exposed 'char *'. > > man2/cacheflush.2 | 24 > 1 file changed, 24 insertions(+) > > diff --git a/man2/cacheflush.2 b/man2/cacheflush.2 > index aba625721..7a2eed506 100644 > --- a/man2/cacheflush.2 > +++ b/man2/cacheflush.2 > @@ -86,6 +86,30 @@ On Linux, this call first appeared on the MIPS > architecture, > but nowadays, Linux provides a > .BR cacheflush () > system call on some other architectures, but with different arguments. > +.SH NOTES > +Unless you need the finer grained control that this system call provides, > +you probably want to use the GCC built-in function > +.BR __builtin___clear_cache (), > +which provides a portable interface > +across platforms supported by GCC and compatible compilers: > +.PP > +.in +4n > +.EX > +.BI "void __builtin___clear_cache(void *" begin ", void *" end ); > +.EE > +.in > +.PP > +On platforms that don't require instruction cache flushes, > +.BR __builtin___clear_cache () > +has no effect. > +.PP > +.IR Note : > +On some GCC-compatible compilers, > +the prototype for this built-in function uses > +.I char * > +instead of > +.I void * > +for the parameters. > .SH BUGS > Linux kernels older than version 2.6.11 ignore the > .I addr > -- Alejandro Colomar Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/ http://www.alejandro-colomar.es/ ___ cfe-users mailing list cfe-users@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-users
