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GCC 16 has changed the semantics of -Wunused-but-set-variable, as well
as introducing new options -Wunused-but-set-variable={0,1,2,3} to
adjust the level of support.
One of the changes is that GCC now treats 'sum += 1' and 'sum++' as
non-usage, whereas clang (and GCC < 16) considers the first as usage
and the second as non-usage, which is sort of inconsistent.
The GCC 16 -Wunused-but-set-variable=2 option implements the previous
semantics of -Wunused-but-set-variable, but since it is a new option,
it cannot be used unconditionally for forward-compatibility, just for
backwards-compatibility.
So this patch adds pragmas to the two self-tests impacted by this,
progs/free_timer.c and progs/rcu_read_lock.c, to make gcc to ignore
-Wunused-but-set-variable warnings when compiling them with GCC > 15.
See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=44677#c25 for details
on why this regression got introduced in GCC upstream.
Signed-off-by: Jose E. Marchesi <jose.marchesi@oracle.com>
Cc: david.faust@oracle.com
Cc: cupertino.miranda@oracle.com
Cc: Eduard Zingerman <eddyz87@gmail.com>
Cc: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20260106173650.18191-2-jose.marchesi@oracle.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
82 lines
1.8 KiB
C
82 lines
1.8 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/* Copyright (C) 2025. Huawei Technologies Co., Ltd */
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#include <linux/bpf.h>
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#include <time.h>
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#include <bpf/bpf_tracing.h>
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#include <bpf/bpf_helpers.h>
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#define MAX_ENTRIES 8
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/* clang considers 'sum += 1' as usage but 'sum++' as non-usage. GCC
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* is more consistent and considers both 'sum += 1' and 'sum++' as
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* non-usage. This triggers warnings in the functions below.
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*
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* Starting with GCC 16 -Wunused-but-set-variable=2 can be used to
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* mimic clang's behavior. */
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#if !defined(__clang__) && __GNUC__ > 15
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#pragma GCC diagnostic ignored "-Wunused-but-set-variable"
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#endif
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struct map_value {
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struct bpf_timer timer;
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};
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struct {
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__uint(type, BPF_MAP_TYPE_HASH);
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__type(key, int);
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__type(value, struct map_value);
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__uint(max_entries, MAX_ENTRIES);
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} map SEC(".maps");
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static int timer_cb(void *map, void *key, struct map_value *value)
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{
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volatile int sum = 0;
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int i;
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bpf_for(i, 0, 1024 * 1024) sum += i;
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return 0;
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}
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static int start_cb(int key)
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{
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struct map_value *value;
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value = bpf_map_lookup_elem(&map, (void *)&key);
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if (!value)
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return 0;
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bpf_timer_init(&value->timer, &map, CLOCK_MONOTONIC);
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bpf_timer_set_callback(&value->timer, timer_cb);
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/* Hope 100us will be enough to wake-up and run the overwrite thread */
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bpf_timer_start(&value->timer, 100000, BPF_F_TIMER_CPU_PIN);
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return 0;
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}
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static int overwrite_cb(int key)
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{
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struct map_value zero = {};
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/* Free the timer which may run on other CPU */
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bpf_map_update_elem(&map, (void *)&key, &zero, BPF_ANY);
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return 0;
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}
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SEC("syscall")
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int BPF_PROG(start_timer)
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{
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bpf_loop(MAX_ENTRIES, start_cb, NULL, 0);
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return 0;
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}
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SEC("syscall")
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int BPF_PROG(overwrite_timer)
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{
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bpf_loop(MAX_ENTRIES, overwrite_cb, NULL, 0);
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return 0;
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}
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char _license[] SEC("license") = "GPL";
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