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* [PATCH v2 bpf-next] libbpf: provide more helpful message on uninitialized global var
@ 2019-07-23 21:11 Andrii Nakryiko
  2019-07-23 22:03 ` Song Liu
  0 siblings, 1 reply; 3+ messages in thread
From: Andrii Nakryiko @ 2019-07-23 21:11 UTC (permalink / raw)
  To: bpf, netdev, ast, daniel, songliubraving
  Cc: andrii.nakryiko, kernel-team, Andrii Nakryiko

When BPF program defines uninitialized global variable, it's put into
a special COMMON section. Libbpf will reject such programs, but will
provide very unhelpful message with garbage-looking section index.

This patch detects special section cases and gives more explicit error
message.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
---
 tools/lib/bpf/libbpf.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 794dd5064ae8..8741c39adb1c 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -1760,15 +1760,22 @@ bpf_program__collect_reloc(struct bpf_program *prog, GElf_Shdr *shdr,
 			 (long long) sym.st_value, sym.st_name, name);
 
 		shdr_idx = sym.st_shndx;
+		insn_idx = rel.r_offset / sizeof(struct bpf_insn);
+		pr_debug("relocation: insn_idx=%u, shdr_idx=%u\n",
+			 insn_idx, shdr_idx);
+
+		if (shdr_idx >= SHN_LORESERVE) {
+			pr_warning("relocation: not yet supported relo for non-static global \'%s\' variable in special section (0x%x) found in insns[%d].code 0x%x\n",
+				   name, shdr_idx, insn_idx,
+				   insns[insn_idx].code);
+			return -LIBBPF_ERRNO__RELOC;
+		}
 		if (!bpf_object__relo_in_known_section(obj, shdr_idx)) {
 			pr_warning("Program '%s' contains unrecognized relo data pointing to section %u\n",
 				   prog->section_name, shdr_idx);
 			return -LIBBPF_ERRNO__RELOC;
 		}
 
-		insn_idx = rel.r_offset / sizeof(struct bpf_insn);
-		pr_debug("relocation: insn_idx=%u\n", insn_idx);
-
 		if (insns[insn_idx].code == (BPF_JMP | BPF_CALL)) {
 			if (insns[insn_idx].src_reg != BPF_PSEUDO_CALL) {
 				pr_warning("incorrect bpf_call opcode\n");
-- 
2.17.1


^ permalink raw reply related	[flat|nested] 3+ messages in thread

* Re: [PATCH v2 bpf-next] libbpf: provide more helpful message on uninitialized global var
  2019-07-23 21:11 [PATCH v2 bpf-next] libbpf: provide more helpful message on uninitialized global var Andrii Nakryiko
@ 2019-07-23 22:03 ` Song Liu
  2019-07-23 23:00   ` Alexei Starovoitov
  0 siblings, 1 reply; 3+ messages in thread
From: Song Liu @ 2019-07-23 22:03 UTC (permalink / raw)
  To: Andrii Nakryiko
  Cc: bpf, netdev, Alexei Starovoitov, daniel, andrii.nakryiko, Kernel Team



> On Jul 23, 2019, at 2:11 PM, Andrii Nakryiko <andriin@fb.com> wrote:
> 
> When BPF program defines uninitialized global variable, it's put into
> a special COMMON section. Libbpf will reject such programs, but will
> provide very unhelpful message with garbage-looking section index.
> 
> This patch detects special section cases and gives more explicit error
> message.
> 
> Signed-off-by: Andrii Nakryiko <andriin@fb.com>

Acked-by: Song Liu <songliubraving@fb.com>

> ---
> tools/lib/bpf/libbpf.c | 13 ++++++++++---
> 1 file changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 794dd5064ae8..8741c39adb1c 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -1760,15 +1760,22 @@ bpf_program__collect_reloc(struct bpf_program *prog, GElf_Shdr *shdr,
> 			 (long long) sym.st_value, sym.st_name, name);
> 
> 		shdr_idx = sym.st_shndx;
> +		insn_idx = rel.r_offset / sizeof(struct bpf_insn);
> +		pr_debug("relocation: insn_idx=%u, shdr_idx=%u\n",
> +			 insn_idx, shdr_idx);
> +
> +		if (shdr_idx >= SHN_LORESERVE) {
> +			pr_warning("relocation: not yet supported relo for non-static global \'%s\' variable in special section (0x%x) found in insns[%d].code 0x%x\n",
> +				   name, shdr_idx, insn_idx,
> +				   insns[insn_idx].code);
> +			return -LIBBPF_ERRNO__RELOC;
> +		}
> 		if (!bpf_object__relo_in_known_section(obj, shdr_idx)) {
> 			pr_warning("Program '%s' contains unrecognized relo data pointing to section %u\n",
> 				   prog->section_name, shdr_idx);
> 			return -LIBBPF_ERRNO__RELOC;
> 		}
> 
> -		insn_idx = rel.r_offset / sizeof(struct bpf_insn);
> -		pr_debug("relocation: insn_idx=%u\n", insn_idx);
> -
> 		if (insns[insn_idx].code == (BPF_JMP | BPF_CALL)) {
> 			if (insns[insn_idx].src_reg != BPF_PSEUDO_CALL) {
> 				pr_warning("incorrect bpf_call opcode\n");
> -- 
> 2.17.1
> 


^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: [PATCH v2 bpf-next] libbpf: provide more helpful message on uninitialized global var
  2019-07-23 22:03 ` Song Liu
@ 2019-07-23 23:00   ` Alexei Starovoitov
  0 siblings, 0 replies; 3+ messages in thread
From: Alexei Starovoitov @ 2019-07-23 23:00 UTC (permalink / raw)
  To: Song Liu, Andrii Nakryiko
  Cc: bpf, netdev, daniel, andrii.nakryiko, Kernel Team

On 7/23/19 3:03 PM, Song Liu wrote:
>> On Jul 23, 2019, at 2:11 PM, Andrii Nakryiko<andriin@fb.com>  wrote:
>>
>> When BPF program defines uninitialized global variable, it's put into
>> a special COMMON section. Libbpf will reject such programs, but will
>> provide very unhelpful message with garbage-looking section index.
>>
>> This patch detects special section cases and gives more explicit error
>> message.
>>
>> Signed-off-by: Andrii Nakryiko<andriin@fb.com>
> Acked-by: Song Liu<songliubraving@fb.com>
> 

Applied. Thanks

^ permalink raw reply	[flat|nested] 3+ messages in thread

end of thread, other threads:[~2019-07-23 23:00 UTC | newest]

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2019-07-23 21:11 [PATCH v2 bpf-next] libbpf: provide more helpful message on uninitialized global var Andrii Nakryiko
2019-07-23 22:03 ` Song Liu
2019-07-23 23:00   ` Alexei Starovoitov

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