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bpf: Minor improvements for bpf_cmp.

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Few minor improvements for bpf_cmp() macro:
. reduce number of args in __bpf_cmp()
. rename NOFLIP to UNLIKELY
. add a comment about 64-bit truncation in "i" constraint
. use "ri" constraint for sizeof(rhs) <= 4
. improve error message for bpf_cmp_likely()

Before:
progs/iters_task_vma.c:31:7: error: variable 'ret' is uninitialized when used here [-Werror,-Wuninitialized]
   31 |                 if (bpf_cmp_likely(seen, <==, 1000))
      |                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../bpf/bpf_experimental.h:325:3: note: expanded from macro 'bpf_cmp_likely'
  325 |                 ret;
      |                 ^~~
progs/iters_task_vma.c:31:7: note: variable 'ret' is declared here
../bpf/bpf_experimental.h:310:3: note: expanded from macro 'bpf_cmp_likely'
  310 |                 bool ret;
      |                 ^

After:
progs/iters_task_vma.c:31:7: error: invalid operand for instruction
   31 |                 if (bpf_cmp_likely(seen, <==, 1000))
      |                     ^
../bpf/bpf_experimental.h:324:17: note: expanded from macro 'bpf_cmp_likely'
  324 |                         asm volatile("r0 " #OP " invalid compare");
      |                                      ^
<inline asm>:1:5: note: instantiated into assembly here
    1 |         r0 <== invalid compare
      |            ^

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/bpf/20240112220134.71209-1-alexei.starovoitov@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Alexei Starovoitov 2024-01-12 14:01:34 -08:00
parent 88031b929c
commit 49c06547d5
1 changed files with 12 additions and 9 deletions
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21
tools/testing/selftests/bpf/bpf_experimental.h
View file

@ -260,11 +260,11 @@ extern void bpf_throw(u64 cookie) __ksym;
#define __is_signed_type(type) (((type)(-1)) < (type)1)
#define __bpf_cmp(LHS, OP, SIGN, PRED, RHS, DEFAULT) \
#define __bpf_cmp(LHS, OP, PRED, RHS, DEFAULT) \
({ \
__label__ l_true; \
bool ret = DEFAULT; \
asm volatile goto("if %[lhs] " SIGN #OP " %[rhs] goto %l[l_true]" \
asm volatile goto("if %[lhs] " OP " %[rhs] goto %l[l_true]" \
:: [lhs] "r"((short)LHS), [rhs] PRED (RHS) :: l_true); \
ret = !DEFAULT; \
l_true: \
@ -276,7 +276,7 @@ l_true: \
* __lhs OP __rhs below will catch the mistake.
* Be aware that we check only __lhs to figure out the sign of compare.
*/
#define _bpf_cmp(LHS, OP, RHS, NOFLIP) \
#define _bpf_cmp(LHS, OP, RHS, UNLIKELY) \
({ \
typeof(LHS) __lhs = (LHS); \
typeof(RHS) __rhs = (RHS); \
@ -285,14 +285,17 @@ l_true: \
(void)(__lhs OP __rhs); \
if (__cmp_cannot_be_signed(OP) || !__is_signed_type(typeof(__lhs))) { \
if (sizeof(__rhs) == 8) \
ret = __bpf_cmp(__lhs, OP, "", "r", __rhs, NOFLIP); \
/* "i" will truncate 64-bit constant into s32, \
* so we have to use extra register via "r". \
*/ \
ret = __bpf_cmp(__lhs, #OP, "r", __rhs, UNLIKELY); \
else \
ret = __bpf_cmp(__lhs, OP, "", "i", __rhs, NOFLIP); \
ret = __bpf_cmp(__lhs, #OP, "ri", __rhs, UNLIKELY); \
} else { \
if (sizeof(__rhs) == 8) \
ret = __bpf_cmp(__lhs, OP, "s", "r", __rhs, NOFLIP); \
ret = __bpf_cmp(__lhs, "s"#OP, "r", __rhs, UNLIKELY); \
else \
ret = __bpf_cmp(__lhs, OP, "s", "i", __rhs, NOFLIP); \
ret = __bpf_cmp(__lhs, "s"#OP, "ri", __rhs, UNLIKELY); \
} \
ret; \
})
@ -304,7 +307,7 @@ l_true: \
#ifndef bpf_cmp_likely
#define bpf_cmp_likely(LHS, OP, RHS) \
({ \
bool ret; \
bool ret = 0; \
if (__builtin_strcmp(#OP, "==") == 0) \
ret = _bpf_cmp(LHS, !=, RHS, false); \
else if (__builtin_strcmp(#OP, "!=") == 0) \
@ -318,7 +321,7 @@ l_true: \
else if (__builtin_strcmp(#OP, ">=") == 0) \
ret = _bpf_cmp(LHS, <, RHS, false); \
else \
(void) "bug"; \
asm volatile("r0 " #OP " invalid compare"); \
ret; \
})
#endif