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Date: Wed, 13 Apr 2016 19:13:59 -0400
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: [PATCH v2] add powerpc64 port
On Thu, Apr 14, 2016 at 01:05:07AM +0200, Szabolcs Nagy wrote:
> * Bobby Bingham <koorogi@...rogi.info> [2016-04-04 00:26:11 -0500]:
> > +++ b/arch/powerpc64/bits/setjmp.h
> > @@ -0,0 +1 @@
> > +typedef unsigned long long __jmp_buf[66];
>
> hm glibc seems to use long[64] with 16byte alignment,
> is the size diff because of alignment?
Good catch.
> > +#if defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
> > +#define MINSIGSTKSZ 2048
> > +#define SIGSTKSZ 8192
> > +#endif
>
> i think these should be bigger, e.g. follow ppc 4k, 10k
Agreed.
> > +typedef struct {
> > + unsigned long vrregs[32][2];
> > + unsigned _pad[3];
> > + unsigned vrsave;
> > + unsigned vscr;
> > + unsigned _pad2[3];
> > +} vrregset_t;
>
> it seems this type should be 16 byte aligned like elf_vrreg_t
>
> (aarch64 has a similar issue i plan to fix: there we use
> 128bit long double to get correct alignment, but kernel
> and glibc uses __int128 which is visible in public headers.
> in powerpc64 at least __vector128 is not exposed in glibc,
> only 16byte aligned structs.)
I don't know what the best solution here is.
> > +++ b/arch/powerpc64/bits/syscall.h
> > @@ -0,0 +1,718 @@
> > +#define __NR_restart_syscall 0
> > +#define __NR_exit 1
> > +#define __NR_fork 2
> ....
> > +#define SYS_restart_syscall __NR_restart_syscall
> > +#define SYS_exit __NR_exit
> > +#define SYS_fork __NR_fork
>
> i prefer SYS_ to use numbers too (easier to update for me),
> but it should be probably fixed together across archs.
I want to replace arch/*/bits/syscall.h with .in files that get
processed as something like:
sed -e p -e s/__NR_/SYS_/ < $< > $@
This would reduce the source tree size a lot and eliminate the risk of
inconsistency.
> > +++ b/arch/powerpc64/reloc.h
> > @@ -0,0 +1,32 @@
> > +#include <endian.h>
> > +
> > +#if __BYTE_ORDER == __LITTLE_ENDIAN
> > +#define ENDIAN_SUFFIX "le"
> > +#else
> > +#define ENDIAN_SUFFIX ""
> > +#endif
> > +
> > +#define LDSO_ARCH "powerpc64" ENDIAN_SUFFIX
> > +
>
> gcc also has -sf, i'm not sure if we should care about
> ppc64 soft-float
Probably not, but perhaps we should test in configure and reject it if
it's not supported correctly.
> > +#define TPOFF_K (-0x7000)
> > +
> > +#define REL_SYMBOLIC R_PPC64_ADDR64
> > +#define REL_GOT R_PPC64_GLOB_DAT
> > +#define REL_PLT R_PPC64_JMP_SLOT
> > +#define REL_RELATIVE R_PPC64_RELATIVE
> > +#define REL_COPY R_PPC64_COPY
> > +#define REL_DTPMOD R_PPC64_DTPMOD64
> > +#define REL_DTPOFF R_PPC64_DTPREL64
> > +#define REL_TPOFF R_PPC64_TPREL64
>
> this reminds me that ppc(64) now has a tls optimization
> if the module is tagged with DT_PPC(64)_OPT, we don't
> need to implement it yet, but eventually elf.h should
> be updated.
Details?
> > +++ b/src/fenv/powerpc64/fenv.c
> > @@ -0,0 +1,68 @@
> > +#define _GNU_SOURCE
> > +#include <fenv.h>
> > +
> > +static inline double get_fpscr_f(void)
> > +{
> > + double d;
> > + __asm__ __volatile__("mffs %0" : "=d"(d));
> > + return d;
> > +}
> > +
> > +static inline long get_fpscr(void)
> > +{
> > + return (union {double f; long i;}) {get_fpscr_f()}.i;
> > +}
> > +
> > +static inline void set_fpscr_f(double fpscr)
> > +{
> > + __asm__ __volatile__("mtfsf 255, %0" : : "d"(fpscr));
> > +}
> > +
> > +static void set_fpscr(long fpscr)
> > +{
> > + set_fpscr_f((union {long i; double f;}) {fpscr}.f);
> > +}
> > +
>
> yes now that .c is allowed under arch/ dirs, it
> makes sense to do fenv with such set/get_fpscr
Yes. At some point it would be nice to make it so most archs can just
define inline functions to load/store their fpu control/status
registers, and a generic fenv.c can implement all the functions. A few
weird archs (x86) would still need custom versions to be efficient but
most could use the generic framework. But this change should not be a
blocker for ppc64. I like the above approach fine for now.
Rich
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