linux-kernel - Re: [PATCH bpf-next v3 2/6] resolve_btfids: Factor out load

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Message-ID: <fb8c16dc-07ee-48bb-a370-0a4931dbba08@linux.dev>
Date: Fri, 5 Dec 2025 15:12:01 -0800
From: Ihor Solodrai <ihor.solodrai@...ux.dev>
To: bot+bpf-ci@...nel.org, ast@...nel.org, daniel@...earbox.net,
 andrii@...nel.org, martin.lau@...ux.dev, eddyz87@...il.com, song@...nel.org,
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Cc: bpf@...r.kernel.org, dwarves@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
 martin.lau@...nel.org, clm@...a.com
Subject: Re: [PATCH bpf-next v3 2/6] resolve_btfids: Factor out load_btf()

On 12/5/25 2:57 PM, bot+bpf-ci@...nel.org wrote:
>> diff --git a/tools/bpf/resolve_btfids/main.c b/tools/bpf/resolve_btfids/main.c
>> index 164f0c941f04..b4caae1170dd 100644
>> --- a/tools/bpf/resolve_btfids/main.c
>> +++ b/tools/bpf/resolve_btfids/main.c
> 
> [ ... ]
> 
>> @@ -529,16 +532,10 @@ static int symbols_collect(struct object *obj)
>>  	return 0;
>>  }
>>
>> -static int symbols_resolve(struct object *obj)
>> +static int load_btf(struct object *obj)
>>  {
>> -	int nr_typedefs = obj->nr_typedefs;
>> -	int nr_structs  = obj->nr_structs;
>> -	int nr_unions   = obj->nr_unions;
>> -	int nr_funcs    = obj->nr_funcs;
>> -	struct btf *base_btf = NULL;
>> -	int err, type_id;
>> -	struct btf *btf;
>> -	__u32 nr_types;
>> +	struct btf *base_btf = NULL, *btf = NULL;
>> +	int err;
>>
>>  	if (obj->base_btf_path) {
>>  		base_btf = btf__parse(obj->base_btf_path, NULL);
>>  		err = libbpf_get_error(base_btf);
>>  		if (err) {
>>  			pr_err("FAILED: load base BTF from %s: %s\n",
>>  			       obj->base_btf_path, strerror(-err));
>> -			return -1;
>> +			goto out_err;
>>  		}
>>  	}
>>
>>  	btf = btf__parse_split(obj->btf_path ?: obj->path, base_btf);
>>  	err = libbpf_get_error(btf);
>>  	if (err) {
>>  		pr_err("FAILED: load BTF from %s: %s\n",
>>  			obj->btf_path ?: obj->path, strerror(-err));
>> -		goto out;
>> +		goto out_err;
>>  	}
>>
>> +	obj->base_btf = base_btf;
>> +	obj->btf = btf;
>> +
>> +	return 0;
>> +
>> +out_err:
>> +	btf__free(base_btf);
>> +	btf__free(btf);
>> +	return err;
> 
> Can btf__free() safely handle ERR_PTR values here?
> 
> When btf__parse() fails on line 541, it returns ERR_PTR(-err), and
> libbpf_get_error() extracts the error code, but base_btf still holds
> the ERR_PTR value. The error path then calls btf__free(base_btf)
> where base_btf is ERR_PTR rather than NULL or a valid pointer.
> 
> The same issue occurs if btf__parse_split() fails on line 550, where
> btf contains ERR_PTR when btf__free(btf) is called.
> 
> In the old code at symbols_resolve(), if base_btf was ERR_PTR, the
> function would return -1 immediately without calling btf__free(),
> avoiding this issue. The new error handling with goto out_err changes
> this behavior.

That's a good observation. Interesting that AI noticed this only on
third try, probably due to changes in prompts.

btf__free() checks for error values [1], so this is not an issue.

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/lib/bpf/btf.c?h=v6.18#n968

> 
>> +}
>> +
>> +static int symbols_resolve(struct object *obj)
>> +{
>> +	int nr_typedefs = obj->nr_typedefs;
>> +	int nr_structs  = obj->nr_structs;
>> +	int nr_unions   = obj->nr_unions;
>> +	int nr_funcs    = obj->nr_funcs;
>> +	struct btf *btf = obj->btf;
>> +	int err, type_id;
>> +	__u32 nr_types;
>> +
>>  	err = -1;
>>  	nr_types = btf__type_cnt(btf);
> 
> [ ... ]
> 
> 
> ---
> AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
> See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md
> 
> CI run summary: https://github.com/kernel-patches/bpf/actions/runs/19978081551