This is the mail archive of the
libc-alpha@sourceware.org
mailing list for the glibc project.
Re: [PATCH] S/390: Fix makecontext with uc_link == NULL
On 07/16/2012 04:28 PM, Thomas Schwinge wrote:
Hi!
On Mon, 16 Jul 2012 13:25:07 +0200, Andreas Krebbel <krebbel@linux.vnet.ibm.com> wrote:
On 07/16/2012 10:19 AM, Thomas Schwinge wrote:
On Thu, 12 Jul 2012 09:38:35 -0400, Carlos O'Donell <carlos_odonell@mentor.com> wrote:
On 7/12/2012 8:19 AM, Andreas Krebbel wrote:
Do we have a testcase that covers this failure?
If we don't, could you try to work one up?
stdlib/tst-makecontext already calls makecontext with uc_link == NULL
but the function invoked in the context does explicitly call exit (0).
Removing this enables the testcase to cover that problem as well.
* stdlib/tst-makecontext.c: Remove explicit exit call.
Excellent. The testcase changes look good to me and match what
SuSv2 says about a returning from a context where uc_link is
zero e.g. "the thread will exit when this context returns."
I'm happy with this, thanks for enhancing the testcase to cover
the failure scenario.
I already raised this topic in
<http://news.gmane.org/find-root.php?message_id=%3C87lijq5h72.fsf@schwinge.name%3E>:
| [a bug is only seen] when returning from a context with Âuc_link ==
| NULLÂ, which is not exercised in the testsuite.
|
| I first though about simply removing the Âexit (0)Â from
| stdlib/tst-makecontext.c:cf (which would then test exactly this case),
| but apparently it is not specified which status value to use for exit in
| this case -- libc.info: ÂIf `uc_link' was a null pointer the application
| terminates in this case. -- so it is not trivial to test for. (Maybe
| worth specifying? EXIT_SUCCESS (0)?)
Ok. Thanks for the pointer. I think everything other than 0 doesn't make much sense since
exiting that way is not caused by any kind of error.
Ack.
I could check in the testcase change removing the exit and we could make the back-end
maintainers aware of the problem with their target. What do you think?
How about this one?
manual: setcontext: Clarify termination when uc_link is the null pointer.
2012-07-16 Thomas Schwinge <thomas@codesourcery.com>
Andreas Krebbel <Andreas.Krebbel@de.ibm.com>
* manual/setjmp.texi (setcontext): Clarify normal process
termination when uc_link is the null pointer.
* stdlib/tst-makecontext.c (cf): Exercise this: remove explicit
exit call.
diff --git a/manual/setjmp.texi b/manual/setjmp.texi
index a5a7ce6..f13ac7b 100644
--- a/manual/setjmp.texi
+++ b/manual/setjmp.texi
@@ -354,7 +354,8 @@ specified parameters passed. If this function returns execution is
resumed in the context which was referenced by the @code{uc_link}
element of the context structure passed to @code{makecontext} at the
time of the call. If @code{uc_link} was a null pointer the application
-terminates in this case.
+terminates normally with an exit status value of @code{EXIT_SUCCESS}
+(@pxref{Program Termination}).
Since the context contains information about the stack no two threads
should use the same context at the same time. The result in most cases
diff --git a/stdlib/tst-makecontext.c b/stdlib/tst-makecontext.c
index 3185900..eb6e89b 100644
--- a/stdlib/tst-makecontext.c
+++ b/stdlib/tst-makecontext.c
@@ -35,7 +35,9 @@ cf (int i)
printf ("i %d thr %d\n", i, thr);
exit (1);
}
- exit (0);
+
+ /* Since uc_link below has been set to NULL, setcontext is supposed to
+ terminate the process normally after this function returns. */
}
int
x86_64: makecontext: exit (0) if uc_link is the null pointer.
2012-07-16 Thomas Schwinge <thomas@codesourcery.com>
* sysdeps/unix/sysv/linux/x86_64/__start_context.S
(__start_context): Preserve zero value for regular exit case.
Yes, this is fine.
diff --git a/sysdeps/unix/sysv/linux/x86_64/__start_context.S b/sysdeps/unix/sysv/linux/x86_64/__start_context.S
index 77d322e..9f2ee23 100644
--- a/sysdeps/unix/sysv/linux/x86_64/__start_context.S
+++ b/sysdeps/unix/sysv/linux/x86_64/__start_context.S
@@ -39,8 +39,9 @@ ENTRY(__start_context)
call JUMPTARGET(__setcontext)
/* If this returns (which can happen if the syscall fails) we'll
exit the program with the return error value (-1). */
+ movq %rax,%rdi
-2: movq %rax,%rdi
+2:
call HIDDEN_JUMPTARGET(exit)
/* The 'exit' call should never return. In case it does cause
the process to terminate. */
SH: makecontext: exit (0) if uc_link is the null pointer.
2012-07-16 Thomas Schwinge <thomas@codesourcery.com>
* sysdeps/unix/sysv/linux/sh/makecontext.S (.Lexitcode): Preserve
zero value for regular exit case.
diff --git a/sysdeps/unix/sysv/linux/sh/makecontext.S b/sysdeps/unix/sysv/linux/sh/makecontext.S
index a04bc9f..73fca8b 100644
--- a/sysdeps/unix/sysv/linux/sh/makecontext.S
+++ b/sysdeps/unix/sysv/linux/sh/makecontext.S
@@ -128,6 +128,7 @@ ENTRY(__makecontext)
cfi_restore (pr)
/* If this returns (which can happen if the syscall fails) we'll exit
the program with the return error value (-1). */
+ mov r0, r4
2:
mov.l .Lexit, r1
@@ -135,7 +136,7 @@ ENTRY(__makecontext)
add r12, r1
#endif
jsr @r1
- mov r0, r4
+ nop
/* The 'exit' call should never return. In case it does cause the
process to terminate. */
ABORT_INSTRUCTION_ASM
I suggest the sh maintainer to review this, it looks fine to me,
thanks,
Andreas
Further (incomplete) notes for port maintainers have been gives as
follows:
i386: sysdeps/unix/sysv/linux/i386/makecontext.S:L(exitcode): seems OK
x86_64: sysdeps/unix/sysv/linux/x86_64/__start_context.S: 2: is misplaced, should be after the movq %rax, %rdi
SPARC32: sysdeps/unix/sysv/linux/sparc/sparc32/setcontext.S:__start_context can't tell
SPARC64: sysdeps/unix/sysv/linux/sparc/sparc64/makecontext.c:__makecontext_ret missing handling completely
S390-32: sysdeps/unix/sysv/linux/s390/s390-32/makecontext.c:__makecontext_ret missing handling completely
S390-64: sysdeps/unix/sysv/linux/s390/s390-64/makecontext.c:__makecontext_ret missing handling completely
GrÃÃe,
Thomas
--
Andreas Jaeger aj@{suse.com,opensuse.org} Twitter/Identica: jaegerandi
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 NÃrnberg, Germany
GF: Jeff Hawn,Jennifer Guild,Felix ImendÃrffer,HRB16746 (AG NÃrnberg)
GPG fingerprint = 93A3 365E CE47 B889 DF7F FED1 389A 563C C272 A126