Re: [PATCH bpf-next 0/4] bpf: arm64: Indirect jumps

[Anton Protopopov <a.s.protopopov@gmail.com>]

On 25/11/17 12:46AM, Puranjay Mohan wrote:
> This set adds the support of indirect jumps to the arm64 JIT. It
> involves calling bpf_prog_update_insn_ptrs() to support instructions
> array map. The second piece is supporting BPF_JMP|BPF_X|BPF_JA, SRC=0,
> DST=Rx, off=0, imm=0 instruction that is trivial to implement on arm64.
>
> When running the selftests after doing the above changes, I found that
> on arm64 builds of llvm, a relocation section was being generated for
> .jumptables sections and it was making libbpf fail like:
> 
> libbpf: relocation against STT_SECTION in non-exec section is not supported!
> Error: failed to link 'tools/testing/selftests/bpf/cpuv4/bpf_gotox.bpf.o': Invalid argument (22)
> 
> Which is due to:
> 
> Relocation section '.rel.jumptables' at offset 0x5b50 contains 263 entries:
>     Offset             Info             Type               Symbol's Value  Symbol's Name
> 0000000000000000  0000000300000002 R_BPF_64_ABS64         0000000000000000 syscall
> 0000000000000008  0000000300000002 R_BPF_64_ABS64         0000000000000000 syscall
> 0000000000000010  0000000300000002 R_BPF_64_ABS64         0000000000000000 syscall
> 
> This rel section is not generated by x86 builds of LLVM. The third patch
> of this set makes libbpf ignore relocation sections for .jumptables.

I added Yonghong to this thread. He had fixed this problem in
https://github.com/llvm/llvm-project/pull/166301 changes doesn't seem to be
x86-specific...

> 
> The final patch enables selftests on arm64:
> 
>  [root@localhost bpf]# ./test_progs-cpuv4 -a "*gotox*"
>  #20/1    bpf_gotox/one-switch:OK
>  #20/2    bpf_gotox/one-switch-non-zero-sec-offset:OK
>  #20/3    bpf_gotox/two-switches:OK
>  #20/4    bpf_gotox/big-jump-table:OK
>  #20/5    bpf_gotox/static-global:OK
>  #20/6    bpf_gotox/nonstatic-global:OK
>  #20/7    bpf_gotox/other-sec:OK
>  #20/8    bpf_gotox/static-global-other-sec:OK
>  #20/9    bpf_gotox/nonstatic-global-other-sec:OK
>  #20/10   bpf_gotox/one-jump-two-maps:OK
>  #20/11   bpf_gotox/one-map-two-jumps:OK
>  #20      bpf_gotox:OK
>  #537/1   verifier_gotox/jump_table_ok:OK
>  #537/2   verifier_gotox/jump_table_reserved_field_src_reg:OK
>  #537/3   verifier_gotox/jump_table_reserved_field_non_zero_off:OK
>  #537/4   verifier_gotox/jump_table_reserved_field_non_zero_imm:OK
>  #537/5   verifier_gotox/jump_table_no_jump_table:OK
>  #537/6   verifier_gotox/jump_table_incorrect_dst_reg_type:OK
>  #537/7   verifier_gotox/jump_table_invalid_read_size_u32:OK
>  #537/8   verifier_gotox/jump_table_invalid_read_size_u16:OK
>  #537/9   verifier_gotox/jump_table_invalid_read_size_u8:OK
>  #537/10  verifier_gotox/jump_table_misaligned_access:OK
>  #537/11  verifier_gotox/jump_table_invalid_mem_acceess_pos:OK
>  #537/12  verifier_gotox/jump_table_invalid_mem_acceess_neg:OK
>  #537/13  verifier_gotox/jump_table_add_sub_ok:OK
>  #537/14  verifier_gotox/jump_table_no_writes:OK
>  #537/15  verifier_gotox/jump_table_use_reg_r0:OK
>  #537/16  verifier_gotox/jump_table_use_reg_r1:OK
>  #537/17  verifier_gotox/jump_table_use_reg_r2:OK
>  #537/18  verifier_gotox/jump_table_use_reg_r3:OK
>  #537/19  verifier_gotox/jump_table_use_reg_r4:OK
>  #537/20  verifier_gotox/jump_table_use_reg_r5:OK
>  #537/21  verifier_gotox/jump_table_use_reg_r6:OK
>  #537/22  verifier_gotox/jump_table_use_reg_r7:OK
>  #537/23  verifier_gotox/jump_table_use_reg_r8:OK
>  #537/24  verifier_gotox/jump_table_use_reg_r9:OK
>  #537/25  verifier_gotox/jump_table_outside_subprog:OK
>  #537/26  verifier_gotox/jump_table_contains_non_unique_values:OK
>  #537     verifier_gotox:OK
>  Summary: 2/37 PASSED, 0 SKIPPED, 0 FAILED

Cool!

> Puranjay Mohan (4):
>   bpf: arm64: Add support for instructions array
>   bpf: arm64: Add support for indirect jumps
>   libbpf: Ignore relocations for .jumptables sections
>   selftests: bpf: Enable gotox tests from arm64
> 
>  arch/arm64/net/bpf_jit_comp.c                      | 11 +++++++++++
>  tools/lib/bpf/linker.c                             |  4 ++++
>  tools/testing/selftests/bpf/progs/verifier_gotox.c |  4 ++--
>  3 files changed, 17 insertions(+), 2 deletions(-)
> 
> -- 
> 2.47.3
>