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-id = 2304
-title = "Disabling SVE via `-cpu max,sve=off` leaves SVE2 advertised by `getauxval`"
-state = "closed"
-created_at = "2024-04-23T12:16:36.267Z"
-closed_at = "2024-08-01T08:31:57.918Z"
-labels = ["Closed::Fixed", "linux-user", "target: arm"]
-url = "https://gitlab.com/qemu-project/qemu/-/issues/2304"
-host-os = "Ubuntu 22.04"
-host-arch = "x86_64"
-qemu-version = "qemu-aarch64 version 8.2.94"
-guest-os = "n/a"
-guest-arch = "n/a"
-description = """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."""
-reproduce = "n/a"
-additional = "n/a"