On Sat, 27 May 2023, Rémi Denis-Courmont wrote:
Le perjantaina 26. toukokuuta 2023, 11.03.14 EEST Martin Storsjö a écrit :
Based on code by Janne Grunau.
Using HWCAP_CPUID for user space access to the CPU feature registers. See
https://www.kernel.org/doc/html/latest/arm64/cpu-feature-registers.html.
---
configure | 2 ++
libavutil/aarch64/cpu.c | 38 ++++++++++++++++++++++++++++++++++++++
2 files changed, 40 insertions(+)
diff --git a/configure b/configure
index 3c7473efb2..b5357b8d27 100755
--- a/configure
+++ b/configure
@@ -2207,6 +2207,7 @@ HAVE_LIST_PUB="
HEADERS_LIST="
arpa_inet_h
+ asm_hwcap_h
asm_types_h
cdio_paranoia_h
cdio_paranoia_paranoia_h
@@ -6422,6 +6423,7 @@ check_headers io.h
enabled libdrm &&
check_headers linux/dma-buf.h
+check_headers asm/hwcap.h
check_headers linux/perf_event.h
check_headers libcrystalhd/libcrystalhd_if.h
check_headers malloc.h
diff --git a/libavutil/aarch64/cpu.c b/libavutil/aarch64/cpu.c
index 42b33e4a2d..34c838c2f5 100644
--- a/libavutil/aarch64/cpu.c
+++ b/libavutil/aarch64/cpu.c
@@ -20,6 +20,42 @@
#include "libavutil/cpu_internal.h"
#include "config.h"
+#if (defined(__linux__) || defined(__ANDROID__)) && HAVE_GETAUXVAL &&
HAVE_ASM_HWCAP_H +#include <stdint.h>
+#include <asm/hwcap.h>
+#include <sys/auxv.h>
+
+#define get_cpu_feature_reg(reg, val) \
+ __asm__("mrs %0, " #reg : "=r" (val))
Strictly speaking, this can read any system register. One way to prevent that
would be to include the ID_ prefix and _EL1 suffix in the macro. I would have
used a pure static inline instead, but that's just a matter of taste.
+
+static int detect_flags(void)
+{
+ unsigned long ret = getauxval(AT_HWCAP);
+ int flags = 0;
+#if defined(HWCAP_CPUID)
+ uint64_t tmp;
+ if (!(ret & HWCAP_CPUID))
+ return flags;
+ get_cpu_feature_reg(ID_AA64ISAR0_EL1, tmp);
+ if (((tmp >> 44) & 0xf) == 0x1)
+ flags |= AV_CPU_FLAG_DOTPROD;
+ get_cpu_feature_reg(ID_AA64ISAR1_EL1, tmp);
+ if (((tmp >> 52) & 0xf) == 0x1)
+ flags |= AV_CPU_FLAG_I8MM;
+#endif
NEON detection could be added here, though I've yet to see an Armv8
implementation without AdvSIMD.
I guess we could, but as it's part of the require baseline for armv8-a I
don't think there's much need for it? If configured with --disable-neon we
don't return that cpuflag though.
FWIW, DotProd is exposed as HWCAP_ASIMDDP and I8MM is exposed via
HWCAP2_I8MM, using trapped ID registers is not (yet) necessary.
Ah, I see. I guess using those would be more straightforward.
OTOH, HWCAP_CPUID is available much earlier than HWCAP_ASIMDDP or
HWCAP2_I8MM (I do some amount of cross building with a fairly old
sysroot). I'll think about it, whether it's worth complicating things to
try both approaches, or if we should just go with the plain HWCAPs here.
// Martin
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