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Re: [PATCH] Use unaligned memory accesses unconditionally
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From: |
Jean Delvare |
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Subject: |
Re: [PATCH] Use unaligned memory accesses unconditionally |
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Date: |
Tue, 8 Aug 2023 10:12:38 +0200 |
Hi Fangrui,
On Wed, 2 Aug 2023 17:18:46 +0000, Fangrui Song via dmidecode-devel wrote:
> Currently ALIGNMENT_WORKAROUND is only defined for __ia64__ and __arm__.
> However, -fsanitize=alignment (part of UndefinedBehaviorSanitizer) will
> give errors for other architectures like x86. Modern compilers are able
> to optimize the memory access, so let's just use unaligned memory
> accesses unconditionally.
I'm not sure what qualifies as a "modern compiler" for you, but on my
up-to-date openSUSE Leap 15.4 system, gcc 7.5.0 x86_64 builds very
different, much larger, and 0.8% slower code with
-DALIGNMENT_WORKAROUND:
add/remove: 0/0 grow/shrink: 9/0 up/down: 5099/0 (5099)
Function old new delta
dmi_table_decode 24440 27760 +3320
dmi_decode_oem 8475 9806 +1331
dmi_print_cpuid 434 626 +192
smbios3_decode 369 481 +112
smbios_decode 569 625 +56
legacy_decode 300 348 +48
dmi_processor_family 536 560 +24
dmi_processor_frequency 86 94 +8
dmi_get_cpuid_type.isra 379 387 +8
Total: Before=60630, After=65729, chg +8.41%
Therefore I'm not willing to apply your patch.
--
Jean Delvare
SUSE L3 Support