On Mon, Nov 14, 2016 at 04:04:04PM -0500, Shware Systems wrote:
> Technically, it doesn't
> match. The #defines after provide matching labels for symbolic references, so
> portable source most likely will compile, but using a field not listed for an
> si_code value (with an intent of temporary storage, perhaps, rather than
> increase the frame size for automatic variables) risks overwriting values
> that are pertinent to that code, or reading invalid values. The method can
> save space for packed allocations, usually "a good thing", at the expense of
> precluding some forms of algorithm optimizations.
The spec says that all members must be part of the structure. It does't mean
that they each need unique storage _at the same time_. Only the fields relevent
to the signal that caused siginfo_t to be presented to the application need be
valid for that signal.
Note that Unix and linux systems have used a union to represent this for
many years.
scott
>
> On Monday, November 14, 2016 FELLIN, JEFF K (JEFF) (JEFF)
> <j...@research.att.com> wrote:
>
> As I read this information from signal.h :
>
> ??
>
> [CX] The <signal.h> header shall define the siginfo_t type as a structure,
> which shall include at least the following members:
>
> [CX]
> int???????????????????? si_signo ??Signal number.
> int???????????????????? si_code?? ??Signal code.
>
> [XSI]
> int???????????????????? si_errno ??If non-zero, an errno value associated
> with
> ????????????????????????????????????????????????this signal, as described in
> <errno.h>.
>
> [CX]
> pid_t???????????????? si_pid???? ??Sending process ID.
> uid_t???????????????? si_uid???? ??Real user ID of sending process.
> void???????????????? *si_addr?? ??Address of faulting instruction.
> int???????????????????? si_status Exit value or signal.
>
> [OB XSR]
> long?????????????????? si_band?? ??Band event for SIGPOLL.
>
> [CX]
> union sigval?? si_value ??Signal value.
>
> ??
> ??
>
> All of the above members MUST be available in all occurrences of siginfo_t,
> whether or not they are applicable on a specific signal.
>
> ??
>
> So can someone tell me how this siginfo_t definition matches the minimum set
> of members for ALL instances of siginfo_t?
>
> ??
>
> typedef struct siginfo
>
> ?? {
>
> ?????? int si_signo;???????????????????????????? /* Signal number.?? */
>
> ?????? int si_errno;???????????????????????????? /* If non-zero, an errno
> value associated with
>
> ???????????????????????????????????????????????????????????????????? this
> signal, as defined in <errno.h>.?? */
>
> ?????? int si_code;?????????????????????????????? /* Signal code.?? */
>
> ??
>
> ?????? union
>
> ?????????? {
>
> ?????????????? int _pad[__SI_PAD_SIZE];
>
> ??
>
> ???????????????? /* kill().?? */
>
> ?????????????? struct
>
> ?????????????????? {
>
> ?????????????????????? __pid_t si_pid;???????? /* Sending process ID.?? */
>
> ?????????????????????? __uid_t si_uid;???????? /* Real user ID of sending
> process.?? */
>
> ?????????????????? } _kill;
>
> ??
>
> ?????????????? /* POSIX.1b timers.?? */
>
> ?????????????? struct
>
> ?? ????????????????{
>
> ?????????????????????? int si_tid;???????????????? /* Timer ID.?? */
>
> ?????????????????????? int si_overrun;???????? /* Overrun count.?? */
>
> ?????????????????????? sigval_t si_sigval; /* Signal value.?? */
>
> ?????????????????? } _timer;
>
> ??
>
> ?????????????? /* POSIX.1b signals.?? */
>
> ?????????????? struct
>
> ?????????????????? {
>
> ???????????????? ??????__pid_t si_pid;???????? /* Sending process ID.?? */
>
> ?????????????????????? __uid_t si_uid;???????? /* Real user ID of sending
> process.?? */
>
> ?????????????????????? sigval_t si_sigval; /* Signal value.?? */
>
> ?????????????????? } _rt;
>
> ??
>
> ?????????????? /* SIGCHLD.?? */
>
> ?????????????? struct
>
> ?????????????????? {
>
> ?????????????????????? __pid_t si_pid;???????? /* Which child.?? */
>
> ?????????????????????? __uid_t si_uid;???????? /* Real user ID of sending
> process.?? */
>
> ?????????????????????? int si_status;?????????? /* Exit value or signal.?? */
>
> ?????????????????????? __clock_t si_utime;
>
> ?????????????????????? __clock_t si_stime;
>
> ???????????? ??????} _sigchld;
>
> ???????????? /* SIGILL, SIGFPE, SIGSEGV, SIGBUS.?? */
>
> ?????????????? struct
>
> ?????????????????? {
>
> ?????????????????????? void *si_addr;?????????? /* Faulting insn/memory
> ref.?? */
>
> ?????????????????? } _sigfault;
>
> ??
>
> ?????????????? /* SIGPOLL.?? */
>
> ?????????????? struct
>
> ?????????????????? {
>
> ?????????????????????? long int si_band;???? /* Band event for SIGPOLL.?? */
>
> ?????????????????????? int si_fd;
>
> ?????????????????? } _sigpoll;
>
> ?????????? } _sifields;
>
> ?? } siginfo_t;
>
> ??
>
> ??
>
> /* X/Open requires some more fields with fixed names.?? */
>
> # define si_pid???????????????? _sifields._kill.si_pid
>
> # define si_uid???????????????? _sifields._kill.si_uid
>
> # define si_timerid???????? _sifields._timer.si_tid
>
> # define si_overrun???????? _sifields._timer.si_overrun
>
> # define si_status?????????? _sifields._sigchld.si_status
>
> # define si_utime???????????? _sifields._sigchld.si_utime
>
> # define si_stime???????????? _sifields._sigchld.si_stime
>
> # define si_value???????????? _sifields._rt.si_sigval
>
> # define si_int???????????????? _sifields._rt.si_sigval.sival_int
>
> # define si_ptr???????????????? _sifields._rt.si_sigval.sival_ptr
>
> # define si_addr?????????????? _sifields._sigfault.si_addr
>
> # define si_band?????????????? _sifields._sigpoll.si_band
>
> # define si_fd?????????????????? _sifields._sigpoll.si_fd
>
> ??
>
> Jeff Fellin
>
