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aarch64: Use future HWCAP2_MTE in ifunc resolver

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Make glibc MTE-safe on systems where MTE is available. This allows
using heap tagging with an LD_PRELOADed malloc implementation that
enables MTE. We don't document this as guaranteed contract yet, so
glibc may not be MTE safe when HWCAP2_MTE is set (older glibcs
certainly aren't). This is mainly for testing and debugging.

The HWCAP flag is not exposed in public headers until Linux adds it
to its uapi. The HWCAP value reservation will be in Linux 5.9.
This commit is contained in:
Szabolcs Nagy 2020-07-24 12:37:23 +01:00
parent 180d5a045f
commit 2dc33b928b
1 changed files with 8 additions and 2 deletions
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10
sysdeps/aarch64/multiarch/strlen.c
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@ -26,8 +26,14 @@
# include <string.h>
# include <init-arch.h>
/* This should check HWCAP_MTE when it is available. */
#define MTE_ENABLED() (false)
/* This should check HWCAP2_MTE when it is available: current
linux kernel does not expose it, but its value is reserved.
This is needed to make glibc MTE-safe on future systems in
case user code enables MTE. The ABI contract for enabling
MTE is not yet specified, but it can be useful for at least
debugging which does not need a contract. */
#define FUTURE_HWCAP2_MTE (1 << 18)
#define MTE_ENABLED() (GLRO(dl_hwcap2) & FUTURE_HWCAP2_MTE)
extern __typeof (__redirect_strlen) __strlen;