GNU bug report logs - #76360
cksum crc broken with VMULL on musl

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Alyssa Ross <hi <at> alyssa.is>
To: bug-coreutils <at> gnu.org
Subject: cksum crc broken with VMULL on musl
Date: Mon, 17 Feb 2025 10:26:15 +0100

[Message part 1 (text/plain, inline)]

On aarch64-unknown-linux-musl, cksum -a crc seems to be producing the
wrong values with coreutils 9.6, causing tests/cksum/cksum.sh to fail.
I bisected this to the following commit:

commit d155be4a22cdc5d271a74c2ae8226c4239ab76ed (HEAD)
Author: Sam Russell <sam.h.russell <at> gmail.com>
Date:   Thu Nov 28 20:28:21 2024 +0100

    cksum: use ARMv8 SIMD extensions
    
    * configure.ac: Add check for ARMv8 VMULL support.
    * src/cksum.c: Add ARMv8 VMULL detection function.
    * src/cksum.h: Add ARMv8 VMULL implementation declaration.
    * src/cksum_vmull.c: ARMv8 VMULL implementation.
    * src/local.mk: Add build flags for ARMv8 VMULL.
    * NEWS: Mention the ARMv8 SIMD improvement.

If I configure with utils_cv_vmull_intrinsic_exists=no the test passes.
Relevant portion of test-suite.log follows.  I think the "missing: No
such file or directory" is an unrelated incorrect use of the _returns
function?

FAIL: tests/cksum/cksum
=======================

cksum: missing: No such file or directory
--- exp	2025-02-17 09:18:57.198429856 +0000
+++ out	2025-02-17 09:18:57.198429856 +0000
@@ -1 +1 @@
-3720986905 65574 in
+2108650022 65574 in
--- exp	2025-02-17 09:18:57.202429997 +0000
+++ out	2025-02-17 09:18:57.202429997 +0000
@@ -1 +1 @@
-4278270357 65664 in
+1411087274 65664 in
FAIL tests/cksum/cksum.sh (exit status: 1)

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Message #8 received at 76360 <at> debbugs.gnu.org (full text, mbox):

From: Alyssa Ross <hi <at> alyssa.is>
To: 76360 <at> debbugs.gnu.org
Subject: [PATCH] cksum: fix shift count overflow
Date: Mon, 17 Feb 2025 11:05:49 +0100

This fixes the following warnings when building for a platform where
uint_fast32_t is 32 bits:

src/cksum_vmull.c: In function 'cksum_vmull':
src/cksum_vmull.c:95:69: warning: left shift count >= width of type [-Wshift-count-overflow]
   95 |           xor_crc = vcombine_u64 (vcreate_u64 (0), vcreate_u64 (crc << 32));
      |                                                                     ^~
src/cksum_vmull.c:196:69: warning: left shift count >= width of type [-Wshift-count-overflow]
  196 |           xor_crc = vcombine_u64 (vcreate_u64 (0), vcreate_u64 (crc << 32));
      |                                                                     ^~

This resulted in cksum -a crc producing incorrect values on musl.
---
 src/cksum_vmull.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/cksum_vmull.c b/src/cksum_vmull.c
index c6f067584..6a87a21ab 100644
--- a/src/cksum_vmull.c
+++ b/src/cksum_vmull.c
@@ -92,7 +92,7 @@ cksum_vmull (FILE *fp, uint_fast32_t *crc_out, uintmax_t *length_out)
           data = bswap_neon (data);
           /* XOR in initial CRC value (for us 0 so no effect), or CRC value
              calculated for previous BUFLEN buffer from fread */
-          xor_crc = vcombine_u64 (vcreate_u64 (0), vcreate_u64 (crc << 32));
+          xor_crc = vcombine_u64 (vcreate_u64 (0), vcreate_u64 ((uint64_t)crc << 32));
           crc = 0;
           data = veorq_u64 (data, xor_crc);
           data3 = vld1q_u64 ((uint64_t *) (datap + 1));
@@ -193,7 +193,7 @@ cksum_vmull (FILE *fp, uint_fast32_t *crc_out, uintmax_t *length_out)
         {
           data = vld1q_u64 ((uint64_t *) (datap));
           data = bswap_neon (data);
-          xor_crc = vcombine_u64 (vcreate_u64 (0), vcreate_u64 (crc << 32));
+          xor_crc = vcombine_u64 (vcreate_u64 (0), vcreate_u64 ((uint64_t)crc << 32));
           crc = 0;
           data = veorq_u64 (data, xor_crc);
           while (bytes_read >= 32)

base-commit: d155be4a22cdc5d271a74c2ae8226c4239ab76ed
-- 
2.47.2

Message #11 received at 76360 <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Alyssa Ross <hi <at> alyssa.is>
Cc: 76360 <at> debbugs.gnu.org
Subject: Re: bug#76360: cksum crc broken with VMULL on musl
Date: Mon, 17 Feb 2025 02:34:11 -0800

[Message part 1 (text/plain, inline)]

Thanks for the bug report. I installed the attached patches; please give 
them a try, as I don't have easy access to that platform.

[0001-cksum-fix-test-for-missing.patch (text/x-patch, attachment)]

[0002-cksum-port-to-32-bit-uint_fast32_t.patch (text/x-patch, attachment)]

Message #14 received at 76360 <at> debbugs.gnu.org (full text, mbox):

From: Alyssa Ross <hi <at> alyssa.is>
To: Paul Eggert <eggert <at> cs.ucla.edu>
Cc: 76360 <at> debbugs.gnu.org
Subject: Re: bug#76360: cksum crc broken with VMULL on musl
Date: Mon, 17 Feb 2025 11:59:05 +0100

[Message part 1 (text/plain, inline)]

Paul Eggert <eggert <at> cs.ucla.edu> writes:

> Thanks for the bug report. I installed the attached patches; please give 
> them a try, as I don't have easy access to that platform.

Both patches do what they're supposed to, thanks!

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