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- All what you never wanted to know about sigaction(),
- struct sigaction, and sigset_t.
-
-
-Before vda started messing with sigset_t, struct sigaction
-and sigaction() functions, things looked this way:
-
-
- Structures
-
-MIPS:
-
-Ignoring bogus "#if defined(__mips__) ..." block in
-libc/sysdeps/linux/common/bits/kernel_sigaction.h
-and using
-libc/sysdeps/linux/mips/bits/kernel_sigaction.h
-as an authoritative source:
-
-HAVE_SA_RESTORER is #defined
-struct old_kernel_sigaction {
- unsigned sa_flags;
- sighandler_t k_sa_handler;
- unsigned long sa_mask;
- unsigned pad0[3]; /* reserved, keep size constant */
- /* Abi says here follows reserved int[2] */
- void (*sa_restorer)(void);
-#if (_MIPS_SZPTR < 64)
- /* For 32 bit code we have to pad struct sigaction to get
- * constant size for the ABI */
- int pad1[1]; /* reserved */
-#endif
-};
-struct kernel_sigaction {
- unsigned int sa_flags;
- sighandler_t k_sa_handler;
- kernel_sigset_t sa_mask;
- void (*sa_restorer)(void);
- int s_resv[1]; /* reserved */
-};
-struct sigaction {
- unsigned sa_flags;
- sighandler_t sa_handler;
- sigset_t sa_mask;
- /* The ABI says here are two unused ints following. */
- /* Restore handler. */
- void (*sa_restorer)(void);
-#if _MIPS_SZPTR < 64
- int sa_resv[1];
-#endif
-};
-
-IA64:
-
-Has no old_sigaction. What a relief.
-
-struct kernel_sigaction {
- sighandler_t k_sa_handler;
- unsigned long sa_flags;
- sigset_t sa_mask;
-};
-struct sigaction {
- sighandler_t sa_handler;
- unsigned long sa_flags;
- sigset_t sa_mask;
-};
-
-Alpha:
-
-struct old_kernel_sigaction {
- sighandler_t k_sa_handler;
- unsigned long sa_mask;
- unsigned sa_flags;
-};
-struct kernel_sigaction {
- sighandler_t k_sa_handler;
- unsigned sa_flags;
- sigset_t sa_mask;
-};
-struct sigaction {
- sighandler_t sa_handler;
- sigset_t sa_mask;
- unsigned sa_flags;
-};
-
-HPPA:
-
-struct kernel_sigaction {
- sighandler_t k_sa_handler;
- unsigned long sa_flags;
- sigset_t sa_mask;
-};
-struct sigaction {
- sighandler_t sa_handler;
- unsigned long sa_flags;
- sigset_t sa_mask;
-};
-
-The rest, kernel side:
-
-HAVE_SA_RESTORER #defined
-struct old_kernel_sigaction {
- sighandler_t k_sa_handler;
- unsigned long sa_mask;
- unsigned long sa_flags;
- void (*sa_restorer)(void);
-};
-struct kernel_sigaction {
- sighandler_t k_sa_handler;
- unsigned long sa_flags;
- void (*sa_restorer)(void);
- sigset_t sa_mask;
-};
-
-On userspace side, Sparc has special struct sigaction:
-
-struct sigaction {
- sighandler_t sa_handler;
- sigset_t sa_mask;
- unsigned long sa_flags;
- void (*sa_restorer)(void); /* Not used by Linux/Sparc */
-};
-
-And finally the rest has:
-
-struct sigaction {
- sighandler_t sa_handler;
- sigset_t sa_mask;
- int sa_flags;
- void (*sa_restorer)(void);
-};
-
-Userspace sigset_t was uniformly defined as vector of longs
-big enough to hold 1024 (!) bits - carried over from glibc.
-Since the only arch whose struct kernel_sigaction contains sa_mask
-not as a last member is MIPS, MIPS has special kernel_sigset_t,
-which is an array of longs long enough for 128 bits.
-Other arches still used userspace sigset_t in struct kernel_sigaction,
-but it did not really matter because overlong kernel_sigaction
-does not hurt in sigaction() [explained below].
-On kernel side, all arches define _NSIG to 65 (meaning
-there are 64 signals, 1..64) except MIPS, which define it to 129.
-
-
- Functions
-
-sigaction() [libc function] usually has two kernel_sigaction's
-on stack and copy (userspace) struct sigaction members into
-first one, executes syscall, then pulls out the result from
-second one. This accomodates differences in layouts of structs.
-
-The only typically present quirk is what to do with sa_restorer.
-
- libc/sysdeps/linux/arm/sigaction.c
-
-if HAVE_SA_RESTORER and (sa_flags & SA_RESTORER) is not set,
-sets sa_restorer to
-(flags & SA_SIGINFO) ? __default_rt_sa_restorer : __default_sa_restorer,
-and sets SA_RESTORER,
-otherwise passes it as-is. Which is kinda strange, because AFAICS
-HAVE_SA_RESTORER is *not* defined for ARM.
-
- libc/sysdeps/linux/i386/sigaction.c
-
-Forcibly sets SA_RESTORER and sa_restorer:
-kact.sa_flags = act->sa_flags | SA_RESTORER;
-kact.sa_restorer = ((act->sa_flags & SA_SIGINFO) ? &restore_rt : &restore);
-
- libc/sysdeps/linux/x86_64/sigaction.c
-
-Forcibly sets SA_RESTORER and sa_restorer:
-kact.sa_flags = act->sa_flags | SA_RESTORER;
-kact.sa_restorer = &restore_rt;
-
- libc/sysdeps/linux/mips/sigaction.c
-
-# ifdef HAVE_SA_RESTORER
-# if _MIPS_SIM == _ABIO32
- kact.sa_restorer = act->sa_restorer;
-# else
- kact.sa_restorer = &restore_rt;
-# endif
-# endif
-No confusion here, HAVE_SA_RESTORER is #defined for MIPS
-
- libc/sysdeps/linux/avr32/sigaction.c
-
-if (kact.sa_flags & SA_RESTORER) {
- kact.sa_restorer = act->sa_restorer;
-} else {
- kact.sa_restorer = __default_rt_sa_restorer;
- kact.sa_flags |= SA_RESTORER;
-}
-Does not check HAVE_SA_RESTORER, but avr32 falls
-in "completely ordinary" category on both kernel and
-userspace sides, and those have it defined.
-
- libc/sysdeps/linux/xtensa/sigaction.c
-
-if (kact.sa_flags & SA_RESTORER) {
- kact.sa_restorer = act->sa_restorer;
-} else {
- kact.sa_restorer = __default_sa_restorer;
- kact.sa_flags |= SA_RESTORER;
-}
-Thus, similar to avr32.
-
- libc/signal/sigaction.c (i.e. the all other arches)
-
-# ifdef HAVE_SA_RESTORER
- kact.sa_restorer = act->sa_restorer;
-# endif
-Plain translation, just sa_restorer copy is protected
-by HAVE_SA_RESTORER #define check. Looks like here
-HAVE_SA_RESTORER will be undef'ed only for IA64,
-Alpha an HPPA.
-
-
- Proposed overhaul past 0.9.30
-
-Since we can define libc-side structures at will:
-make sigset_t and struct sigaction identical on kernel side and libc side
-within each arch. If arches do not need special handling of sa_restorer,
-then sigaction() can directly use passed struct sigaction as-is.
-Otherwise, a copy is still needed, although sigaction() might have
-just one struct kernel_sigaction on stack and use it both for passing
-data to kernel and for receiving it back. Might save a few bytes.
-
-To this effect:
-
-* Make sigset_t size match kernel side on all arches.
- This is easy since all arches have 64 signals and only MIPS has 128.
-
-* Modify libc/sysdeps/linux/$ARCH/bits/sigaction.h
- so that its struct sigaction matches kernel's. If sa_restorer
- field is present in libc but is missing in kernel_sigaction,
- add it at the bottom in order to not mess up kernel_sigaction layout.
-
-* Modify libc/sysdeps/linux/$ARCH/sigaction.c
- to implement the logic above. In "common" pseudo-arch
- (libc/signal/sigaction.c file),
- we would not even need to do any copying, as described above.
-
-* Document discovered arch quirks while debugging this mess.
-
-* struct old_kernel_sigaction can't be disposed of in a similar way,
- we need to have userspace struct sigaction unchanged regardless
- whether we use "old" or "new" kernel sigaction() syscall.
- It's moot anyway because "old" one is long unused, it's from
- pre-2.2 kernels.
generated by cgit v1.2.3 (git 2.25.1) at 2024-04-27 23:30:24 +0000