On 8/9/21 11:34 AM, Johan Almbladh wrote:
Before, the comments in the 32-bit eBPF JIT claimed that up to
MAX_TAIL_CALL_CNT + 1 tail calls were allowed, when in fact the
implementation was using the correct limit of MAX_TAIL_CALL_CNT.
Now, the comments are in line with what the code actually does.
Signed-off-by: Johan Almbladh <johan.almbladh@xxxxxxxxxxxxxxxxx>
---
arch/x86/net/bpf_jit_comp32.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/arch/x86/net/bpf_jit_comp32.c b/arch/x86/net/bpf_jit_comp32.c
index 3bfda5f502cb..8db9ab11abda 100644
--- a/arch/x86/net/bpf_jit_comp32.c
+++ b/arch/x86/net/bpf_jit_comp32.c
@@ -1272,7 +1272,7 @@ static void emit_epilogue(u8 **pprog, u32 stack_depth)
* ... bpf_tail_call(void *ctx, struct bpf_array *array, u64 index) ...
* if (index >= array->map.max_entries)
* goto out;
- * if (++tail_call_cnt > MAX_TAIL_CALL_CNT)
+ * if (tail_call_cnt++ >= MAX_TAIL_CALL_CNT)
* goto out;
* prog = array->ptrs[index];
* if (prog == NULL)
@@ -1307,7 +1307,7 @@ static void emit_bpf_tail_call(u8 **pprog)
EMIT2(IA32_JBE, jmp_label(jmp_label1, 2));
/*
- * if (tail_call_cnt > MAX_TAIL_CALL_CNT)
+ * if (tail_call_cnt >= MAX_TAIL_CALL_CNT)
* goto out;
*/
lo = (u32)MAX_TAIL_CALL_CNT;
@@ -1321,7 +1321,7 @@ static void emit_bpf_tail_call(u8 **pprog)
/* cmp ecx,lo */
EMIT3(0x83, add_1reg(0xF8, IA32_ECX), lo);
- /* ja out */
+ /* jae out */
EMIT2(IA32_JAE, jmp_label(jmp_label1, 2));
You have me confused here ... b61a28cf11d6 ("bpf: Fix off-by-one in tail call count
limiting") from bpf-next says '[interpreter is now] in line with the behavior of the
x86 JITs'. From the latter I assumed you implicitly refer to x86-64. Which one did you
test specifically wrt the prior statement? It looks like x86-64 vs x86-32 differ:
[...]
EMIT2_off32(0x8B, 0x85, tcc_off); /* mov eax, dword ptr [rbp - tcc_off] */
EMIT3(0x83, 0xF8, MAX_TAIL_CALL_CNT); /* cmp eax, MAX_TAIL_CALL_CNT */
EMIT2(X86_JA, OFFSET2); /* ja out */
EMIT3(0x83, 0xC0, 0x01); /* add eax, 1 */
EMIT2_off32(0x89, 0x85, tcc_off); /* mov dword ptr [rbp - tcc_off], eax */
[...]
So it's ja vs jae ... unless I need more coffee? ;)
/* add eax,0x1 */
