Bug 88093 - setcontext() is not signal safe
setcontext() is not signal safe
Product: Red Hat Linux
Classification: Retired
Component: glibc (Show other bugs)
i386 Linux
medium Severity medium
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Assigned To: Jakub Jelinek
Brian Brock
Depends On:
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Reported: 2003-04-05 10:41 EST by John Reiser
Modified: 2007-04-18 12:52 EDT (History)
0 users

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Fixed In Version:
Doc Type: Bug Fix
Doc Text:
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Last Closed: 2003-04-09 15:21:38 EDT
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Description John Reiser 2003-04-05 10:41:26 EST
From Bugzilla Helper:
User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.0.0) Gecko/20020529

Description of problem:
setcontext() temporarily stores the new register values on the stack at
addresses less than the stack pointer (before 'popa' to set the new values).  If
a signal is delivered between the store and the popa, then the locations that
are read by popa get overwritten, so eventually the wrong values will be set
into the registers.

Version-Release number of selected component (if applicable):

How reproducible:

Steps to Reproduce:
1.Run testcase stdlib/tst-setcontext under gdb.
2.Set a breakpoint at setcontext+67: mov %ebx,(%ecx)
3.Print $ecx and $esp at the breakpoint.


Actual Results:
$esp = 0xffffcb1c
$ecx = 0xffffcafc   # 0x20 less than $esp

Expected Results:
$esp = 0xffffcafc
$ecx = 0xffffcafc  # == $esp

Additional info:

Fix: move the  "movl %ecx, %esp" at line 85 of
sysdeps/unix/sysv/linux/i386/setcontext.S to just after the "subl $36, %ecx" at
line 60.
Comment 1 John Reiser 2003-04-05 23:52:51 EST
A similar problem exists in sysdeps/unix/sysv/linux/i386/swapcontext.S at lines
89 and 114.
Comment 2 Jakub Jelinek 2003-04-09 15:21:38 EDT
An errata has been issued which should help the problem described in this bug report. 
This report is therefore being closed with a resolution of ERRATA. For more information
on the solution and/or where to find the updated files, please follow the link below. You may reopen 
this bug report if the solution does not work for you.


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