netdev - [PATCH bpf] libbpf: Fix libbpf hashmap on (I)LP32 architectures

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Date:   Thu, 9 Jul 2020 15:57:23 -0700
From:   Andrii Nakryiko <andriin@...com>
To:     <bpf@...r.kernel.org>, <netdev@...r.kernel.org>, <ast@...com>,
        <daniel@...earbox.net>, <qboosh@...-linux.org>
CC:     <andrii.nakryiko@...il.com>, <kernel-team@...com>,
        Andrii Nakryiko <andriin@...com>
Subject: [PATCH bpf] libbpf: Fix libbpf hashmap on (I)LP32 architectures

From: Jakub Bogusz <qboosh@...-linux.org>

On ILP32, 64-bit result was shifted by value calculated for 32-bit long type
and returned value was much outside hashmap capacity.
As advised by Andrii Nakryiko, this patch uses different hashing variant for
architectures with size_t shorter than long long.

Fixes: e3b924224028 ("libbpf: add resizable non-thread safe internal hashmap")
Signed-off-by: Jakub Bogusz <qboosh@...-linux.org>
Signed-off-by: Andrii Nakryiko <andriin@...com>
---
 tools/lib/bpf/hashmap.h | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/tools/lib/bpf/hashmap.h b/tools/lib/bpf/hashmap.h
index df59fd4fc95b..e0af36b0e5d8 100644
--- a/tools/lib/bpf/hashmap.h
+++ b/tools/lib/bpf/hashmap.h
@@ -11,14 +11,18 @@
 #include <stdbool.h>
 #include <stddef.h>
 #include <limits.h>
-#ifndef __WORDSIZE
-#define __WORDSIZE (__SIZEOF_LONG__ * 8)
-#endif
 
 static inline size_t hash_bits(size_t h, int bits)
 {
 	/* shuffle bits and return requested number of upper bits */
-	return (h * 11400714819323198485llu) >> (__WORDSIZE - bits);
+#if (__SIZEOF_SIZE_T__ == __SIZEOF_LONG_LONG__)
+	/* LP64 case */
+	return (h * 11400714819323198485llu) >> (__SIZEOF_LONG_LONG__ * 8 - bits);
+#elif (__SIZEOF_SIZE_T__ <= __SIZEOF_LONG__)
+	return (h * 2654435769lu) >> (__SIZEOF_LONG__ * 8 - bits);
+#else
+#	error "Unsupported size_t size"
+#endif
 }
 
 typedef size_t (*hashmap_hash_fn)(const void *key, void *ctx);
-- 
2.24.1