selftests/bpf: Add tests for BPF_DIV and BPF_MOD range tracking

Now BPF_DIV has range tracking support via interval analysis. This patch
adds selftests to cover various cases of BPF_DIV and BPF_MOD operations
when the divisor is a constant, also covering both signed and unsigned variants.

This patch includes several types of tests in 32-bit and 64-bit variants:

1. For UDIV
   - positive divisor
   - zero divisor

2. For SDIV
   - positive divisor, positive dividend
   - positive divisor, negative dividend
   - positive divisor, mixed sign dividend
   - negative divisor, positive dividend
   - negative divisor, negative dividend
   - negative divisor, mixed sign dividend
   - zero divisor
   - overflow (SIGNED_MIN/-1), normal dividend
   - overflow (SIGNED_MIN/-1), constant dividend

3. For UMOD
   - positive divisor
   - positive divisor, small dividend
   - zero divisor

4. For SMOD
   - positive divisor, positive dividend
   - positive divisor, negative dividend
   - positive divisor, mixed sign dividend
   - positive divisor, mixed sign dividend, small dividend
   - negative divisor, positive dividend
   - negative divisor, negative dividend
   - negative divisor, mixed sign dividend
   - negative divisor, mixed sign dividend, small dividend
   - zero divisor
   - overflow (SIGNED_MIN/-1), normal dividend
   - overflow (SIGNED_MIN/-1), constant dividend

Specifically, these selftests are based on dead code elimination:
If the BPF verifier can precisely analyze the result of BPF_DIV/BPF_MOD
instruction, it can prune the path that leads to an error (here we use
invalid memory access as the error case), allowing the program to pass
verification.

Co-developed-by: Shenghao Yuan <shenghaoyuan0928@163.com>
Signed-off-by: Shenghao Yuan <shenghaoyuan0928@163.com>
Co-developed-by: Tianci Cao <ziye@zju.edu.cn>
Signed-off-by: Tianci Cao <ziye@zju.edu.cn>
Signed-off-by: Yazhou Tang <tangyazhou518@outlook.com>
Link: https://lore.kernel.org/r/20260119085458.182221-3-tangyazhou@zju.edu.cn
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/testing/selftests/bpf/prog_tests/verifier.c

@@ -33,6 +33,7 @@
 #include "verifier_direct_packet_access.skel.h"
 #include "verifier_direct_stack_access_wraparound.skel.h"
 #include "verifier_div0.skel.h"
+#include "verifier_div_mod_bounds.skel.h"
 #include "verifier_div_overflow.skel.h"
 #include "verifier_global_subprogs.skel.h"
 #include "verifier_global_ptr_args.skel.h"
@@ -175,6 +176,7 @@ void test_verifier_d_path(void)               { RUN(verifier_d_path); }
 void test_verifier_direct_packet_access(void) { RUN(verifier_direct_packet_access); }
 void test_verifier_direct_stack_access_wraparound(void) { RUN(verifier_direct_stack_access_wraparound); }
 void test_verifier_div0(void)                 { RUN(verifier_div0); }
+void test_verifier_div_mod_bounds(void)       { RUN(verifier_div_mod_bounds); }
 void test_verifier_div_overflow(void)         { RUN(verifier_div_overflow); }
 void test_verifier_global_subprogs(void)      { RUN(verifier_global_subprogs); }
 void test_verifier_global_ptr_args(void)      { RUN(verifier_global_ptr_args); }