bpf: make list_for_each_entry portable
[Changes from V1:
- The __compat_break has been abandoned in favor of
a more readable can_loop macro that can be used anywhere, including
loop conditions.]
The macro list_for_each_entry is defined in bpf_arena_list.h as
follows:
#define list_for_each_entry(pos, head, member) \
for (void * ___tmp = (pos = list_entry_safe((head)->first, \
typeof(*(pos)), member), \
(void *)0); \
pos && ({ ___tmp = (void *)pos->member.next; 1; }); \
cond_break, \
pos = list_entry_safe((void __arena *)___tmp, typeof(*(pos)), member))
The macro cond_break, in turn, expands to a statement expression that
contains a `break' statement. Compound statement expressions, and the
subsequent ability of placing statements in the header of a `for'
loop, are GNU extensions.
Unfortunately, clang implements this GNU extension differently than
GCC:
- In GCC the `break' statement is bound to the containing "breakable"
context in which the defining `for' appears. If there is no such
context, GCC emits a warning: break statement without enclosing `for'
o `switch' statement.
- In clang the `break' statement is bound to the defining `for'. If
the defining `for' is itself inside some breakable construct, then
clang emits a -Wgcc-compat warning.
This patch adds a new macro can_loop to bpf_experimental, that
implements the same logic than cond_break but evaluates to a boolean
expression. The patch also changes all the current instances of usage
of cond_break withing the header of loop accordingly.
Tested in bpf-next master.
No regressions.
Signed-off-by: Jose E. Marchesi <jose.marchesi@oracle.com>
Cc: david.faust@oracle.com
Cc: cupertino.miranda@oracle.com
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Link: https://lore.kernel.org/r/20240511212243.23477-1-jose.marchesi@oracle.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
diff --git a/tools/testing/selftests/bpf/bpf_arena_list.h b/tools/testing/selftests/bpf/bpf_arena_list.h
index b99b9f4..85dbc3e 100644
--- a/tools/testing/selftests/bpf/bpf_arena_list.h
+++ b/tools/testing/selftests/bpf/bpf_arena_list.h
@@ -29,6 +29,7 @@ static inline void *bpf_iter_num_new(struct bpf_iter_num *it, int i, int j) { re
static inline void bpf_iter_num_destroy(struct bpf_iter_num *it) {}
static inline bool bpf_iter_num_next(struct bpf_iter_num *it) { return true; }
#define cond_break ({})
+#define can_loop true
#endif
/* Safely walk link list elements. Deletion of elements is allowed. */
@@ -36,8 +37,7 @@ static inline bool bpf_iter_num_next(struct bpf_iter_num *it) { return true; }
for (void * ___tmp = (pos = list_entry_safe((head)->first, \
typeof(*(pos)), member), \
(void *)0); \
- pos && ({ ___tmp = (void *)pos->member.next; 1; }); \
- cond_break, \
+ pos && ({ ___tmp = (void *)pos->member.next; 1; }) && can_loop; \
pos = list_entry_safe((void __arena *)___tmp, typeof(*(pos)), member))
static inline void list_add_head(arena_list_node_t *n, arena_list_head_t *h)
diff --git a/tools/testing/selftests/bpf/bpf_experimental.h b/tools/testing/selftests/bpf/bpf_experimental.h
index 8b9cc87..3d9e4b8 100644
--- a/tools/testing/selftests/bpf/bpf_experimental.h
+++ b/tools/testing/selftests/bpf/bpf_experimental.h
@@ -326,19 +326,48 @@ l_true: \
})
#endif
+/*
+ * Note that cond_break can only be portably used in the body of a breakable
+ * construct, whereas can_loop can be used anywhere.
+ */
#ifdef __BPF_FEATURE_MAY_GOTO
+#define can_loop \
+ ({ __label__ l_break, l_continue; \
+ bool ret = true; \
+ asm volatile goto("may_goto %l[l_break]" \
+ :::: l_break); \
+ goto l_continue; \
+ l_break: ret = false; \
+ l_continue:; \
+ ret; \
+ })
+
#define cond_break \
({ __label__ l_break, l_continue; \
- asm volatile goto("may_goto %l[l_break]" \
+ asm volatile goto("may_goto %l[l_break]" \
:::: l_break); \
goto l_continue; \
l_break: break; \
l_continue:; \
})
#else
+#define can_loop \
+ ({ __label__ l_break, l_continue; \
+ bool ret = true; \
+ asm volatile goto("1:.byte 0xe5; \
+ .byte 0; \
+ .long ((%l[l_break] - 1b - 8) / 8) & 0xffff; \
+ .short 0" \
+ :::: l_break); \
+ goto l_continue; \
+ l_break: ret = false; \
+ l_continue:; \
+ ret; \
+ })
+
#define cond_break \
({ __label__ l_break, l_continue; \
- asm volatile goto("1:.byte 0xe5; \
+ asm volatile goto("1:.byte 0xe5; \
.byte 0; \
.long ((%l[l_break] - 1b - 8) / 8) & 0xffff; \
.short 0" \
diff --git a/tools/testing/selftests/bpf/progs/arena_list.c b/tools/testing/selftests/bpf/progs/arena_list.c
index c0422c5..93bd060 100644
--- a/tools/testing/selftests/bpf/progs/arena_list.c
+++ b/tools/testing/selftests/bpf/progs/arena_list.c
@@ -49,7 +49,7 @@ int arena_list_add(void *ctx)
list_head = &global_head;
- for (i = zero; i < cnt; cond_break, i++) {
+ for (i = zero; i < cnt && can_loop; i++) {
struct elem __arena *n = bpf_alloc(sizeof(*n));
test_val++;
diff --git a/tools/testing/selftests/bpf/progs/verifier_iterating_callbacks.c b/tools/testing/selftests/bpf/progs/verifier_iterating_callbacks.c
index 99e561f..bd676d7 100644
--- a/tools/testing/selftests/bpf/progs/verifier_iterating_callbacks.c
+++ b/tools/testing/selftests/bpf/progs/verifier_iterating_callbacks.c
@@ -318,7 +318,7 @@ int cond_break1(const void *ctx)
unsigned long i;
unsigned int sum = 0;
- for (i = zero; i < ARR_SZ; cond_break, i++)
+ for (i = zero; i < ARR_SZ && can_loop; i++)
sum += i;
for (i = zero; i < ARR_SZ; i++) {
barrier_var(i);
@@ -336,12 +336,11 @@ int cond_break2(const void *ctx)
int i, j;
int sum = 0;
- for (i = zero; i < 1000; cond_break, i++)
+ for (i = zero; i < 1000 && can_loop; i++)
for (j = zero; j < 1000; j++) {
sum += i + j;
cond_break;
- }
-
+ }
return sum;
}
@@ -349,7 +348,7 @@ static __noinline int loop(void)
{
int i, sum = 0;
- for (i = zero; i <= 1000000; i++, cond_break)
+ for (i = zero; i <= 1000000 && can_loop; i++)
sum += i;
return sum;
