On 26/09/23 19:02, Peter Bergner wrote: > The powerpc toolchain keeps a copy of the HWCAP bit masks in our TCB for fast > access by our __builtin_cpu_supports built-in function. The TCB space for > the HWCAP entries - which are created in pairs - is an ABI extension, so > waiting to create the space for HWCAP3 and HWCAP4 until we need them is > problematical, given distro unwillingness to apply ABI modifying patches > to distro point releases. Define AT_HWCAP3 and AT_HWCAP4 in the generic > uapi header so they can be used in GLIBC to reserve space in the powerpc > TCB for their future use. This is different than previously exported auxv, where each AT_* constant would have a auxv entry. On glibc it would require changing _dl_parse_auxv to iterate over the auxv_values to find AT_HWCAP3/AT_HWCAP4 (not ideal, but doable). Wouldn't be better to always export it on fs/binfmt_elf.c, along with all the machinery to setup it (ELF_HWCAP3, etc), along with proper documentation? > > I scanned both the Linux and GLIBC source codes looking for unused AT_* > values and 29 and 30 did not seem to be used, so they are what I went > with. If anyone sees a problem with using those specific values, I'm > amenable to using other values, just let me know what would be better. > > Peter > > > Signed-off-by: Peter Bergner <bergner@xxxxxxxxxxxxx> > --- > include/uapi/linux/auxvec.h | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/include/uapi/linux/auxvec.h b/include/uapi/linux/auxvec.h > index 6991c4b8ab18..cc61cb9b3e9a 100644 > --- a/include/uapi/linux/auxvec.h > +++ b/include/uapi/linux/auxvec.h > @@ -32,6 +32,8 @@ > #define AT_HWCAP2 26 /* extension of AT_HWCAP */ > #define AT_RSEQ_FEATURE_SIZE 27 /* rseq supported feature size */ > #define AT_RSEQ_ALIGN 28 /* rseq allocation alignment */ > +#define AT_HWCAP3 29 /* extension of AT_HWCAP */ > +#define AT_HWCAP4 30 /* extension of AT_HWCAP */ > > #define AT_EXECFN 31 /* filename of program */ >
