• NAME
  
  sigaltstack - get or set alternate signal stack content
• SYNOPSIS
  
  #include <signal.h>
  
  int sigaltstack(const stack_t * ss, stack_t * oss );
  
  where:

  ss

  points to a signalstack structure defined in <signal.h> containing stack content after the call.

  oss

  if not NULL, points to a signalstack structure containing stack content before the call.

• DESCRIPTION
  
  sigaction(2) may indicate that a signal should execute on an alternate stack. Where this is the case, sigaltstack(2) stores the signal in an alternate stack structure ss where its execution status may be examined prior to processing.
  
  
  
  The sigaltstack struct is defined in <signal.h> as follows:
  
  

  
  
      void       *ss_sp     /* SVID3 uses caddr_t ss_sp
      int        ss_flags
      size_t     ss_size
  

  where:

  ss_sp

  points to the stack structure.

  ss_flags

  specifies the stack state to SS_DISABLE or SS_ONSTACK as follows:
  
  If ss is not NULL,the new state may be set to SS_DISABLE, which specifies that the stack is to be disabled and ss_sp and ss_size are ignored.  If SS_DISABLE is not set, the stack will be enabled.
  
  If oss is not NULL, the stack state may be either SS_ONSTACK or SS_DISABLE. The value SS_ONSTACK indicates that the process is currently executing on the alternate stack and that any attempt to modify it during execution will fail.  The value SS_DISABLE indicates that the current signal stack is disabled.

  ss_size

  specifies the size of the stack.
  
  The value SIGSTKSZ defines the average number of bytes used when allocating an alternate stack area.  The value MINSIGSTKSZ defines the minimum stack size for a signal handler.  When processing an alternate stack size, your program should include these values in the stack requirement to plan for the overhead of the operating system.

• RETURN VALUES
  
  sigaltstack(2) returns 0 on success and -1 on failure.
• ERRORS
  
  sigaltstack(2) sets  errno for the following conditions:

  EINVAL

  ss is not a null pointer the ss_flags member pointed to by ss contains flags other than SS_DISABLE.

  ENOMEM

  The size of the alternate stack area is less than MINSIGSTKSZ.

  EPERM

  An attempt was made to modify an active stack.

• STANDARDS
  
  This function comforms to: XPG4-UNIX.
• SEE ALSO
  
  getcontext(2) , sigaction(2) , sigsetjmp(3) .

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