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| author | Christian Krinitsin <mail@krinitsin.com> | 2025-05-30 16:52:07 +0200 |
|---|---|---|
| committer | Christian Krinitsin <mail@krinitsin.com> | 2025-05-30 16:52:17 +0200 |
| commit | 9260319e7411ff8281700a532caa436f40120ec4 (patch) | |
| tree | 2f6bfe5f3458dd49d328d3a9eb508595450adec0 /gitlab/issues_text/target_arm/host_missing/accel_missing/2304 | |
| parent | 225caa38269323af1bfc2daadff5ec8bd930747f (diff) | |
| download | qemu-analysis-9260319e7411ff8281700a532caa436f40120ec4.tar.gz qemu-analysis-9260319e7411ff8281700a532caa436f40120ec4.zip | |
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Diffstat (limited to 'gitlab/issues_text/target_arm/host_missing/accel_missing/2304')
| -rw-r--r-- | gitlab/issues_text/target_arm/host_missing/accel_missing/2304 | 38 |
1 files changed, 38 insertions, 0 deletions
diff --git a/gitlab/issues_text/target_arm/host_missing/accel_missing/2304 b/gitlab/issues_text/target_arm/host_missing/accel_missing/2304 new file mode 100644 index 000000000..29de268d7 --- /dev/null +++ b/gitlab/issues_text/target_arm/host_missing/accel_missing/2304 @@ -0,0 +1,38 @@ +Disabling SVE via `-cpu max,sve=off` leaves SVE2 advertised by `getauxval` +Description of problem: +The documentation on https://qemu-project.gitlab.io/qemu/system/arm/cpu-features.html suggests that it should be possible to disable SVE support by passing `-cpu max,sve=off` on the command line, however this appears to only disable the SVE support advertised in the return value from `getauxval(AT_HWCAP)`. In particular it leaves SVE2 reported as enabled. This leaves the feature set advertised by `getauxval` in an inconsistent state since SVE is mandatory if SVE2 is available. + +This may also affect other feature dependencies for example FEAT_SVE_BITPerm also requiring SVE2 to be available, I've not checked exhaustively. + +For example, given the following code: + + #include <sys/auxv.h> + #include <stdio.h> + + int main() { + unsigned long hwcap = getauxval(AT_HWCAP); + unsigned long hwcap2 = getauxval(AT_HWCAP2); + + if (hwcap & HWCAP_SVE) { + printf("have sve!\n"); + } else { + printf("don't have sve!\n"); + } + if (hwcap2 & HWCAP2_SVE2) { + printf("have sve2!\n"); + } else { + printf("don't have sve2!\n"); + } + } + +We can observe the following: + + $ aarch64-linux-gnu-gcc test.c -static + $ ../qemu-aarch64 -cpu max ./a.out + have sve! + have sve2! + $ ../qemu-aarch64 -cpu max,sve=off ./a.out + don't have sve! + have sve2! + +I don't believe that there is a `-cpu ...,sve2=off` option, so I would expect that disabling SVE also prevents SVE2 from being advertised as available. |