From d26c924c8cd947e91bd4f5e8d0b7f74d3460d22b Mon Sep 17 00:00:00 2001 From: Ben Pfaff Date: Sat, 24 Mar 2007 01:12:10 +0000 Subject: [PATCH] Explain the semantics of exec in more detail. From Godmar Back. --- doc/userprog.texi | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/doc/userprog.texi b/doc/userprog.texi index 75bc8e5..60a53ee 100644 --- a/doc/userprog.texi +++ b/doc/userprog.texi @@ -616,6 +616,9 @@ Runs the executable whose name is given in @var{cmd_line}, passing any given arguments, and returns the new process's program id (pid). Must return pid -1, which otherwise should not be a valid pid, if the program cannot load or run for any reason. +Thus, the parent process cannot return from the @code{exec} until it +knows whether the child process successfully loaded its executable. +You must use appropriate synchronization to ensure this. @end deftypefn @deftypefn {System Call} int wait (pid_t @var{pid}) @@ -975,6 +978,18 @@ or the machine shuts down. You may modify the stack setup code to allocate more than one page of stack space for each process. In the next project, you will implement a better solution. + +@item What should happen if an @code{exec} fails midway through loading? + +@code{exec} should return -1 if the child process fails to load for +any reason. This includes the case where the load fails part of the +way through the process (e.g.@: where it runs out of memory in the +@code{multi-oom} test). Therefore, the parent process cannot return +from the @code{exec} system call until it is established whether the +load was successful or not. The child must communicate this +information to its parent using appropriate synchronization, such as a +semaphore (@pxref{Semaphores}), to ensure that the information is +communicated without race conditions. @end table @node 80x86 Calling Convention -- 2.30.2