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Bug 2031015 - zlib: Unnecessary IFUNC resolver for crc32_z
Summary: zlib: Unnecessary IFUNC resolver for crc32_z
Keywords:
Status: CLOSED ERRATA
Alias: None
Product: Red Hat Enterprise Linux 8
Classification: Red Hat
Component: zlib
Version: 8.5
Hardware: x86_64
OS: Linux
unspecified
low
Target Milestone: rc
: ---
Assignee: Lukas Javorsky
QA Contact: Dita Stehlikova
URL:
Whiteboard:
Depends On:
Blocks: 2031019
TreeView+ depends on / blocked
 
Reported: 2021-12-10 10:09 UTC by Florian Weimer
Modified: 2024-03-14 04:25 UTC (History)
9 users (show)

Fixed In Version: zlib-1.2.11-25.el8
Doc Type: No Doc Update
Doc Text:
Clone Of:
: 2031019 (view as bug list)
Environment:
Last Closed: 2023-11-14 15:49:21 UTC
Type: Bug
Target Upstream Version:
Embargoed:
pm-rhel: mirror+

Attachments (Terms of Use)
Patch [2/3] to add support to zlib 1.2.11 (106.93 KB, application/octet-stream)
2022-11-28 14:50 UTC, IBM Bug Proxy 		no flags Details
Patch [1/3] to add support to zlib 1.2.11 (9.11 KB, application/octet-stream)
2022-11-28 14:50 UTC, IBM Bug Proxy 		no flags Details
Patch [3/3] to add support to zlib 1.2.11 (1.90 KB, application/octet-stream)
2022-11-28 15:00 UTC, IBM Bug Proxy 		no flags Details
s390x patch, rebased on top of 1.2.11 (15.32 KB, application/mbox)
2023-02-02 22:59 UTC, Ilya Leoshkevich 		no flags Details
View All


Links
System ID Private Priority Status Summary Last Updated
IBM Linux Technology Center 195660 0 None None None 2021-12-13 21:12:38 UTC
Red Hat Issue Tracker RHELPLAN-105354 0 None None None 2021-12-10 10:13:18 UTC
Red Hat Product Errata RHBA-2023:7115 0 None None None 2023-11-14 15:49:32 UTC

Description Florian Weimer 2021-12-10 10:09:46 UTC 
The IFUNC resolver for crc32_z just returns a constant result on x86_64:

(gdb) disassemble/m crc32_z
Dump of assembler code for function crc32_z_ifunc:
261	{
   0x0000000000003280 <+0>:	endbr64 

262	#if _ARCH_PWR8==1
263	#if defined(__BUILTIN_CPU_SUPPORTS__)
264	    if (__builtin_cpu_supports("arch_2_07"))
265	        return crc32_vpmsum;
266	#else
267	    if (getauxval(AT_HWCAP2) & PPC_FEATURE2_ARCH_2_07)
268	        return crc32_vpmsum;
269	#endif
270	#endif /* _ARCH_PWR8 */
271	
272	/* return a function pointer for optimized arches here */
273	
274	#ifdef DYNAMIC_CRC_TABLE
275	    if (crc_table_empty)
276	        make_crc_table();
277	#endif /* DYNAMIC_CRC_TABLE */
278	
279	#ifdef BYFOUR
280	    if (sizeof(void *) == sizeof(ptrdiff_t)) {

281	        z_crc_t endian;

282	
283	        endian = 1;

284	        if (*((unsigned char *)(&endian)))

285	            return crc32_little;
   0x0000000000003284 <+4>:	lea    -0x4eb(%rip),%rax        # 0x2da0 <crc32_little>
   0x000000000000328b <+11>:	retq   
   0x000000000000328c <+0>:	nopl   0x0(%rax)

End of assembler dump.

I assume the IFUNC resolver was added for the s390x optimizations. On x86-64, it is definitely unnecessary, likewise for AArch64. I'll check with IBM regarding the POWER8 check and file a separate bug for that if necessary.

The new IFUNC resolver causes problems with symbol interposition (zlib functions are frequently bundled with other software). ELF dependency tracking in the dynamic loader does not work with interposition, and crashes can be the result. The fix is certainly to hide/rename the other symbols (so that the bundled zlib does not interpose the system implementation), but avoiding the IFUNC resolver where possible prevents these crashes and improves backwards compatibility.
Comment 2 Lukas Javorsky 2021-12-13 10:51:17 UTC 
Just to make it clear, can you please confirm you're talking about optimization that was requested from us in this BUG: bug#1959423?
Comment 3 Florian Weimer 2021-12-13 11:07:53 UTC 
(In reply to Lukas Javorsky from comment #2)
> Just to make it clear, can you please confirm you're talking about
> optimization that was requested from us in this BUG: bug#1959423?

That is a bug for Red Hat Enterprise Linux 9. I was mistaken, and the IFUNC resolver was actually introduced for POWER8 support, as part of bug 1666798.
Comment 5 Tulio Magno Quites Machado Filho 2021-12-13 14:48:39 UTC 
> I was mistaken, and the IFUNC resolver was actually introduced for POWER8 support, as part of bug 1666798.

Indeed. Would you like to mirror this issue to IBM?
Comment 6 Florian Weimer 2021-12-13 16:22:55 UTC 
(In reply to Tulio Magno Quites Machado Filho from comment #5)
> > I was mistaken, and the IFUNC resolver was actually introduced for POWER8 support, as part of bug 1666798.
> 
> Indeed. Would you like to mirror this issue to IBM?

Sure, please go ahead. Thanks.
Comment 7 IBM Bug Proxy 2021-12-16 18:10:33 UTC 
------- Comment From mscastanho 2021-12-16 13:02 EDT-------
As mentioned before, this was added by a patch to provide an optimized version of crc32 for POWER8. There is actually a revised version of that patch waiting for review upstream [1][2]. That one explicitly checks the architecture to make sure it only adds the resolver for powerpc, so should avoid the problem on x86.

Could we use that patch instead?

[1] https://github.com/madler/zlib/pull/478
[2] https://patch-diff.githubusercontent.com/raw/madler/zlib/pull/478.patch
Comment 8 Honza Horak 2022-01-11 18:34:34 UTC 
As already consulted before in case of other similar optimization bugs for zlib, we likely cannot expect the upstream to accept this as zlib upstream is not that active regarding these changes.

Since we have already optimization patches in zlib maintained by IBM, we can likely add this to RHEL (proper re-check whether the patch applies cleanly should likely be still done, but I expect it is prepared carefully).

For the verification -- can we again count on IBM verifying it once we have a testing RPM build?

Anyway, our capacity is already exhausted for RHEL-8.6.0 release and we would like to apply changes in such basic libraries that other components depend on early in the development process (which we're way beyond now). Therefore I'd like to propose this to RHEL-8.7.0. Please, provide more justification if the decision of not fixing this for 8.6.0 has a too negative impact.
Comment 9 IBM Bug Proxy 2022-01-25 15:20:24 UTC 
------- Comment From tulioqm.com 2022-01-25 10:16 EDT-------
> For the verification -- can we again count on IBM verifying it once we have
> a testing RPM build?

Yes. We can test this.

> Anyway, our capacity is already exhausted for RHEL-8.6.0 release and we
> would like to apply changes in such basic libraries that other components
> depend on early in the development process (which we're way beyond now).
> Therefore I'd like to propose this to RHEL-8.7.0. Please, provide more
> justification if the decision of not fixing this for 8.6.0 has a too
> negative impact.

It's unclear to me if this question was targeting IBM.
Anyway, from my point of view, it's OK to delay it for 8.7.
Comment 10 Florian Weimer 2022-01-25 15:29:52 UTC 
(In reply to Honza Horak from comment #8)
> Anyway, our capacity is already exhausted for RHEL-8.6.0 release and we
> would like to apply changes in such basic libraries that other components
> depend on early in the development process (which we're way beyond now).
> Therefore I'd like to propose this to RHEL-8.7.0. Please, provide more
> justification if the decision of not fixing this for 8.6.0 has a too
> negative impact.

Sorry, missed this part before. The partner who reported this has a workaround (which is the right thing to do anyway), so I think we can postpone to 8.7. Thanks.
Comment 12 Lukas Javorsky 2022-10-03 09:10:32 UTC 
Unfortunately, the patch in comment#7 cannot be used due to the fact that it is aimed at zlib-1.2.12 version.

In RHEL-8 and RHEL-9 we ship zlib-1.2.11 version.

Could you please specify what part of the patch you would like us to do downstream?
Due to the complexity of this patch, we cannot rebase it to version 1.2.11, we need the help of the author in order to do this.
Comment 17 IBM Bug Proxy 2022-11-15 03:40:24 UTC 
------- Comment From Rajalakshmi.Srinivasaraghavan 2022-11-14 22:31 EDT-------
Manjunath from IBM is working on this.
Comment 18 IBM Bug Proxy 2022-11-28 14:50:38 UTC 
Created attachment 1928040 [details]
Patch [2/3] to add support to zlib 1.2.11
Comment 19 IBM Bug Proxy 2022-11-28 14:50:39 UTC 
Created attachment 1928041 [details]
Patch [1/3] to add support to zlib 1.2.11
Comment 20 IBM Bug Proxy 2022-11-28 15:00:34 UTC 
Created attachment 1928042 [details]
Patch [3/3] to add support to zlib 1.2.11
Comment 21 IBM Bug Proxy 2022-11-28 15:10:30 UTC 
------- Comment From Manjunath.Matti 2022-11-28 10:02 EDT-------
(In reply to comment #12)
> Manjunath from IBM is working on this.

I have attached the 3 patches, which can be applied to the zlib 1.2.11 sources.

The patches are back ported from the below link.

[1] https://github.com/madler/zlib/pull/478

I have built and just run make test. Looks Ok to me.

------- Comment From Manjunath.Matti 2022-11-28 10:02 EDT-------
(In reply to comment #12)
> Manjunath from IBM is working on this.

I have attached the 3 patches, which can be applied to the zlib 1.2.11 sources.

The patches are back ported from the below link.

[1] https://github.com/madler/zlib/pull/478

I have built and just run make test. Looks Ok to me.
Comment 22 Tulio Magno Quites Machado Filho 2022-11-28 15:21:48 UTC 
Manjunath,

I see you attached 3 patches targeting ppc64le.
These changes will break s390x code.

Is the s390x team also backporting their patches?
Comment 23 IBM Bug Proxy 2022-11-28 18:30:30 UTC 
------- Comment From iii.com 2022-11-28 13:25 EDT-------
Hi,

thanks for the heads up.

https://github.com/iii-i/zlib/releases/tag/crc32vx-v5 applies cleanly on top of the posted patches. My tests also pass.

Best regards,
Ilya
Comment 24 Lukas Javorsky 2022-12-13 13:55:48 UTC 
Hi Ilya,

This patch needs to be rebased on top of the old 1.2.11 zlib version.

We don't have the latest 1.2.13 zlib version in RHEL-8, so could you please rebase it on top of the 1.2.11 version and sent it here?

Thank you
Comment 27 Lukas Javorsky 2023-01-12 13:04:41 UTC 
Gentle ping
Comment 29 Ilya Leoshkevich 2023-02-02 22:59:16 UTC 
Created attachment 1941937 [details]
s390x patch, rebased on top of 1.2.11

You can also find this patch at https://github.com/iii-i/zlib/commits/crc32vx-v5-1.2.11.
Comment 31 Lukas Javorsky 2023-05-16 10:22:45 UTC 
MR: https://gitlab.com/redhat/centos-stream/rpms/zlib/-/merge_requests/27
Comment 33 Lukas Javorsky 2023-05-17 18:52:18 UTC 
Merged
Comment 42 errata-xmlrpc 2023-11-14 15:49:21 UTC 
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory (zlib bug fix and enhancement update), and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2023:7115
Comment 43 Red Hat Bugzilla 2024-03-14 04:25:06 UTC 
The needinfo request[s] on this closed bug have been removed as they have been unresolved for 120 days
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