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@@ -1,249 +0,0 @@
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- All what you never wanted to know about sigaction(),
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- struct sigaction, and sigset_t.
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-
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-
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-Before vda started messing with sigset_t, struct sigaction
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-and sigaction() functions, things looked this way:
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-
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-
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- Structures
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-
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-MIPS:
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-
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-Ignoring bogus "#if defined(__mips__) ..." block in
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-libc/sysdeps/linux/common/bits/kernel_sigaction.h
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-and using
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-libc/sysdeps/linux/mips/bits/kernel_sigaction.h
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-as an authoritative source:
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-
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-HAVE_SA_RESTORER is #defined
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-struct old_kernel_sigaction {
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- unsigned sa_flags;
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- sighandler_t k_sa_handler;
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- unsigned long sa_mask;
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- unsigned pad0[3]; /* reserved, keep size constant */
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- /* Abi says here follows reserved int[2] */
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- void (*sa_restorer)(void);
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-#if (_MIPS_SZPTR < 64)
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- /* For 32 bit code we have to pad struct sigaction to get
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- * constant size for the ABI */
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- int pad1[1]; /* reserved */
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-#endif
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-};
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-struct kernel_sigaction {
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- unsigned int sa_flags;
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- sighandler_t k_sa_handler;
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- kernel_sigset_t sa_mask;
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- void (*sa_restorer)(void);
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- int s_resv[1]; /* reserved */
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-};
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-struct sigaction {
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- unsigned sa_flags;
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- sighandler_t sa_handler;
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- sigset_t sa_mask;
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- /* The ABI says here are two unused ints following. */
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- /* Restore handler. */
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- void (*sa_restorer)(void);
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-#if _MIPS_SZPTR < 64
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- int sa_resv[1];
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-#endif
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-};
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-
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-IA64:
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-
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-Has no old_sigaction. What a relief.
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-
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-struct kernel_sigaction {
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- sighandler_t k_sa_handler;
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- unsigned long sa_flags;
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- sigset_t sa_mask;
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-};
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-struct sigaction {
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- sighandler_t sa_handler;
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- unsigned long sa_flags;
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- sigset_t sa_mask;
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-};
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-
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-Alpha:
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-
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-struct old_kernel_sigaction {
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- sighandler_t k_sa_handler;
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- unsigned long sa_mask;
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- unsigned sa_flags;
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-};
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-struct kernel_sigaction {
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- sighandler_t k_sa_handler;
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- unsigned sa_flags;
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- sigset_t sa_mask;
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-};
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-struct sigaction {
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- sighandler_t sa_handler;
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- sigset_t sa_mask;
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- unsigned sa_flags;
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-};
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-
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-HPPA:
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-
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-struct kernel_sigaction {
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- sighandler_t k_sa_handler;
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- unsigned long sa_flags;
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- sigset_t sa_mask;
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-};
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-struct sigaction {
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- sighandler_t sa_handler;
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- unsigned long sa_flags;
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- sigset_t sa_mask;
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-};
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-
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-The rest, kernel side:
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-
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-HAVE_SA_RESTORER #defined
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-struct old_kernel_sigaction {
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- sighandler_t k_sa_handler;
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- unsigned long sa_mask;
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- unsigned long sa_flags;
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- void (*sa_restorer)(void);
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-};
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-struct kernel_sigaction {
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- sighandler_t k_sa_handler;
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- unsigned long sa_flags;
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- void (*sa_restorer)(void);
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- sigset_t sa_mask;
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-};
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-
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-On userspace side, Sparc has special struct sigaction:
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-
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-struct sigaction {
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- sighandler_t sa_handler;
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- sigset_t sa_mask;
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- unsigned long sa_flags;
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- void (*sa_restorer)(void); /* Not used by Linux/Sparc */
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-};
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-
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-And finally the rest has:
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-
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-struct sigaction {
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- sighandler_t sa_handler;
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- sigset_t sa_mask;
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- int sa_flags;
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- void (*sa_restorer)(void);
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-};
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-
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-Userspace sigset_t was uniformly defined as vector of longs
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-big enough to hold 1024 (!) bits - carried over from glibc.
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-Since the only arch whose struct kernel_sigaction contains sa_mask
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-not as a last member is MIPS, MIPS has special kernel_sigset_t,
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-which is an array of longs long enough for 128 bits.
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-Other arches still used userspace sigset_t in struct kernel_sigaction,
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-but it did not really matter because overlong kernel_sigaction
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-does not hurt in sigaction() [explained below].
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-On kernel side, all arches define _NSIG to 65 (meaning
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-there are 64 signals, 1..64) except MIPS, which define it to 129.
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-
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-
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- Functions
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-
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-sigaction() [libc function] usually has two kernel_sigaction's
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-on stack and copy (userspace) struct sigaction members into
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-first one, executes syscall, then pulls out the result from
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-second one. This accomodates differences in layouts of structs.
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-
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-The only typically present quirk is what to do with sa_restorer.
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-
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- libc/sysdeps/linux/arm/sigaction.c
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-
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-if HAVE_SA_RESTORER and (sa_flags & SA_RESTORER) is not set,
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-sets sa_restorer to
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-(flags & SA_SIGINFO) ? __default_rt_sa_restorer : __default_sa_restorer,
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-and sets SA_RESTORER,
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-otherwise passes it as-is. Which is kinda strange, because AFAICS
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-HAVE_SA_RESTORER is *not* defined for ARM.
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-
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- libc/sysdeps/linux/i386/sigaction.c
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-
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-Forcibly sets SA_RESTORER and sa_restorer:
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-kact.sa_flags = act->sa_flags | SA_RESTORER;
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-kact.sa_restorer = ((act->sa_flags & SA_SIGINFO) ? &restore_rt : &restore);
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-
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- libc/sysdeps/linux/x86_64/sigaction.c
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-
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-Forcibly sets SA_RESTORER and sa_restorer:
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-kact.sa_flags = act->sa_flags | SA_RESTORER;
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-kact.sa_restorer = &restore_rt;
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-
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- libc/sysdeps/linux/mips/sigaction.c
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-
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-# ifdef HAVE_SA_RESTORER
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-# if _MIPS_SIM == _ABIO32
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- kact.sa_restorer = act->sa_restorer;
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-# else
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- kact.sa_restorer = &restore_rt;
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-# endif
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-# endif
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-No confusion here, HAVE_SA_RESTORER is #defined for MIPS
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-
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- libc/sysdeps/linux/avr32/sigaction.c
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-
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-if (kact.sa_flags & SA_RESTORER) {
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- kact.sa_restorer = act->sa_restorer;
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-} else {
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- kact.sa_restorer = __default_rt_sa_restorer;
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- kact.sa_flags |= SA_RESTORER;
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-}
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-Does not check HAVE_SA_RESTORER, but avr32 falls
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-in "completely ordinary" category on both kernel and
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-userspace sides, and those have it defined.
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-
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- libc/sysdeps/linux/xtensa/sigaction.c
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-
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-if (kact.sa_flags & SA_RESTORER) {
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- kact.sa_restorer = act->sa_restorer;
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-} else {
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- kact.sa_restorer = __default_sa_restorer;
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- kact.sa_flags |= SA_RESTORER;
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-}
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-Thus, similar to avr32.
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-
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- libc/signal/sigaction.c (i.e. the all other arches)
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-
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-# ifdef HAVE_SA_RESTORER
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- kact.sa_restorer = act->sa_restorer;
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-# endif
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-Plain translation, just sa_restorer copy is protected
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-by HAVE_SA_RESTORER #define check. Looks like here
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-HAVE_SA_RESTORER will be undef'ed only for IA64,
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-Alpha an HPPA.
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-
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-
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- Proposed overhaul past 0.9.30
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-
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-Since we can define libc-side structures at will:
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-make sigset_t and struct sigaction identical on kernel side and libc side
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-within each arch. If arches do not need special handling of sa_restorer,
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-then sigaction() can directly use passed struct sigaction as-is.
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-Otherwise, a copy is still needed, although sigaction() might have
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-just one struct kernel_sigaction on stack and use it both for passing
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-data to kernel and for receiving it back. Might save a few bytes.
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-
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-To this effect:
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-
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-* Make sigset_t size match kernel side on all arches.
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- This is easy since all arches have 64 signals and only MIPS has 128.
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-
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-* Modify libc/sysdeps/linux/$ARCH/bits/sigaction.h
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- so that its struct sigaction matches kernel's. If sa_restorer
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- field is present in libc but is missing in kernel_sigaction,
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- add it at the bottom in order to not mess up kernel_sigaction layout.
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-
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-* Modify libc/sysdeps/linux/$ARCH/sigaction.c
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- to implement the logic above. In "common" pseudo-arch
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- (libc/signal/sigaction.c file),
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- we would not even need to do any copying, as described above.
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-
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-* Document discovered arch quirks while debugging this mess.
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-
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-* struct old_kernel_sigaction can't be disposed of in a similar way,
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- we need to have userspace struct sigaction unchanged regardless
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- whether we use "old" or "new" kernel sigaction() syscall.
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- It's moot anyway because "old" one is long unused, it's from
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- pre-2.2 kernels.
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Waldemar Brodkorb