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From: H.J. Lu <hjl@sourceware.org> To: glibc-cvs@sourceware.org Subject: [glibc] x86: Check the lower byte of EAX of CPUID leaf 2 [BZ #30643] Date: Tue, 29 Aug 2023 19:58:00 +0000 (GMT) [thread overview] Message-ID: <20230829195800.2476B3858D20@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=1493622f4f9048ffede3fbedb64695efa49d662a commit 1493622f4f9048ffede3fbedb64695efa49d662a Author: H.J. Lu <hjl.tools@gmail.com> Date: Mon Aug 28 12:08:14 2023 -0700 x86: Check the lower byte of EAX of CPUID leaf 2 [BZ #30643] The old Intel software developer manual specified that the low byte of EAX of CPUID leaf 2 returned 1 which indicated the number of rounds of CPUDID leaf 2 was needed to retrieve the complete cache information. The newer Intel manual has been changed to that it should always return 1 and be ignored. If the lower byte isn't 1, CPUID leaf 2 can't be used. In this case, we ignore CPUID leaf 2 and use CPUID leaf 4 instead. If CPUID leaf 4 doesn't contain the cache information, cache information isn't available at all. This addresses BZ #30643. Diff: --- sysdeps/x86/dl-cacheinfo.h | 31 +++++++++++++------------------ 1 file changed, 13 insertions(+), 18 deletions(-) diff --git a/sysdeps/x86/dl-cacheinfo.h b/sysdeps/x86/dl-cacheinfo.h index 5ddb35c9d9..87486054f9 100644 --- a/sysdeps/x86/dl-cacheinfo.h +++ b/sysdeps/x86/dl-cacheinfo.h @@ -187,7 +187,7 @@ intel_check_word (int name, unsigned int value, bool *has_level_2, ++round; } /* There is no other cache information anywhere else. */ - break; + return -1; } else { @@ -257,28 +257,23 @@ handle_intel (int name, const struct cpu_features *cpu_features) /* OK, we can use the CPUID instruction to get all info about the caches. */ - unsigned int cnt = 0; - unsigned int max = 1; long int result = 0; bool no_level_2_or_3 = false; bool has_level_2 = false; + unsigned int eax; + unsigned int ebx; + unsigned int ecx; + unsigned int edx; + __cpuid (2, eax, ebx, ecx, edx); - while (cnt++ < max) + /* The low byte of EAX of CPUID leaf 2 should always return 1 and it + should be ignored. If it isn't 1, use CPUID leaf 4 instead. */ + if ((eax & 0xff) != 1) + return intel_check_word (name, 0xff, &has_level_2, &no_level_2_or_3, + cpu_features); + else { - unsigned int eax; - unsigned int ebx; - unsigned int ecx; - unsigned int edx; - __cpuid (2, eax, ebx, ecx, edx); - - /* The low byte of EAX in the first round contain the number of - rounds we have to make. At least one, the one we are already - doing. */ - if (cnt == 1) - { - max = eax & 0xff; - eax &= 0xffffff00; - } + eax &= 0xffffff00; /* Process the individual registers' value. */ result = intel_check_word (name, eax, &has_level_2,
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