Red Hat Bugzilla – Bug 163306
Reading or assigning global h_errno variable causes a memory violation report from mudflap
Last modified: 2009-01-09 01:53:28 EST
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Description of problem:
Simply reading or writing to the h_errno global variable gives out a read/write violation in mudflap.
Version-Release number of selected component (if applicable):
Steps to Reproduce:
1. Compile the program
and the program
h_errno = 0;
with mudflap enabled, i.e.
gcc -fmudflap prog1.c -lmudflap -o prog1
gcc -fmudflap prog2.c -lmudflap -o prog2
2. Run prog1 and prog2.
Actual Results: When prog1 is run, this is what I get:
mudflap violation 1 (check/read): time=1121380261.574621 ptr=0xb7eff6b4 size=4
pc=0xb7f09322 location=`a.cpp:6 (main)'
Nearby object 1: checked region begins 17B after and ends 20B after
mudflap object 0x80cb430: name=`errno area'
bounds=[0xb7eff6a0,0xb7eff6a3] size=4 area=static check=0r/0w liveness=0
alloc time=1121380261.574591 pc=0xb7f09e0a
number of nearby objects: 1
When prog2 is run, the report is similar, but it says "(check/write)", instead of "(check/read)" -- because h_errno is written to.
Expected Results: There should have been no violation messages.
That's a mudflap bug. (*__h_errno_location()) (which is what h_errno expands
to) is a thread local storage variable similarly to errno (*__errno_location()).
libmudflap has special quirks for errno, but not for h_errno (and I guess
not for _res either, and I wonder if any other thread local storage variable).
Jakub, cool, thanks! May I ask why the need for h_errno to expand to a thread
local storage variable if gethostbyname is not reentrant, and it (global
h_errno) isn't used by the reentrant equivalent gethostbyname_r?
h_errno is used in many other functions, some of which are reentrant.
Is there a complete list of such variables someplace? Failing that, I'll add
h_errno support to gcc mainline, and consider backporting.
mudflap is very buggy atm, i get violations just reading from argv :)
(In reply to comment #5)
> mudflap is very buggy atm, i get violations just reading from argv :)
This would be a separate problem. Make sure you pass -fmudflap to the link
stage too. If you do, and you still encounter this, please open a separate
bugzilla with a sample program.
This report targets the FC3 or FC4 products, which have now been EOL'd.
Could you please check that it still applies to a current Fedora release, and
either update the target product or close it ?
this bug is still present in Fedora 8, gcc-4.1.2-33
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