Commit 10563759 authored by Vegard Nossum's avatar Vegard Nossum Committed by Luis Henriques

uml: flush stdout before forking

commit 0754fb29 upstream.

I was seeing some really weird behaviour where piping UML's output
somewhere would cause output to get duplicated:

  $ ./vmlinux | head -n 40
  Checking that ptrace can change system call numbers...Core dump limits :
          soft - 0
          hard - NONE
  OK
  Checking syscall emulation patch for ptrace...Core dump limits :
          soft - 0
          hard - NONE
  OK
  Checking advanced syscall emulation patch for ptrace...Core dump limits :
          soft - 0
          hard - NONE
  OK
  Core dump limits :
          soft - 0
          hard - NONE

This is because these tests do a fork() which duplicates the non-empty
stdout buffer, then glibc flushes the duplicated buffer as each child
exits.

A simple workaround is to flush before forking.
Signed-off-by: default avatarVegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: default avatarRichard Weinberger <richard@nod.at>
Signed-off-by: default avatarLuis Henriques <luis.henriques@canonical.com>
parent c4a74527
...@@ -95,6 +95,8 @@ static int start_ptraced_child(void) ...@@ -95,6 +95,8 @@ static int start_ptraced_child(void)
{ {
int pid, n, status; int pid, n, status;
fflush(stdout);
pid = fork(); pid = fork();
if (pid == 0) if (pid == 0)
ptrace_child(); ptrace_child();
......
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