Re: [PATCH v4] pahole: fix discarded-qualifiers for strchr/strstr.

On 11/03/2026 14:09, d.hourtoulle wrote:
> From: Damien Hourtoulle <[email protected]>
> 
> Glibc 2.43 added C23 const-preserving overloads :
> https://sourceware.org/glibc/wiki/Release/2.43.
> 
> For the function prototype__new, fix local variable declaration to use
> the correct const char* type instead of char*, removing the need to
> discard the const qualifier.
> 
> Also fix a pre-existing bug in type__find_type_enum: when iterating
> over a '+'-concatenated list of enum names, after advancing to the next
> segment the new separator was not nullified, causing "second+third" to
> be passed to cu__find_enumeration_by_name instead of "second".  Add a
> null check before writing to sep_mutable to avoid a null dereference
> when no further '+' is present.
> 
> Signed-off-by: Damien Hourtoulle <[email protected]>

applied, thanks!

> ---
>  btf_encoder.c |  2 +-
>  pahole.c      | 35 ++++++++++++++++++-----------------
>  2 files changed, 19 insertions(+), 18 deletions(-)
> 
> diff --git a/btf_encoder.c b/btf_encoder.c
> index aa7cd1c..d36984a 100644
> --- a/btf_encoder.c
> +++ b/btf_encoder.c
> @@ -1218,7 +1218,7 @@ static bool str_contains_non_fn_suffix(const char *str) {
>  		".cold",
>  		".part"
>  	};
> -	char *suffix = strchr(str, '.');
> +	const char *suffix = strchr(str, '.');
>  	int i;
>  
>  	if (!suffix)
> diff --git a/pahole.c b/pahole.c
> index 02a0d19..e4bfb69 100644
> --- a/pahole.c
> +++ b/pahole.c
> @@ -2483,7 +2483,7 @@ static int64_t type_instance__int_value(struct type_instance *instance, const ch
>  	int byte_offset = 0;
>  
>  	if (!member) {
> -		char *sep = strchr(member_name_orig, '.');
> +		const char *sep = strchr(member_name_orig, '.');
>  
>  		if (!sep)
>  			return -1;
> @@ -2496,8 +2496,8 @@ static int64_t type_instance__int_value(struct type_instance *instance, const ch
>  		char *member_name = member_name_alloc;
>  		struct type *type = instance->type;
>  
> -		sep = member_name_alloc + (sep - member_name_orig);
> -		*sep = 0;
> +		char *sep_mutable = member_name_alloc + (sep - member_name_orig);  // sep mutable for the copy
> +		*sep_mutable = 0;
>  
>  		while (1) {
>  			member = type__find_member_by_name(type, member_name);
> @@ -2510,9 +2510,9 @@ out_free_member_name:
>  			type = tag__type(cu__type(cu, member->tag.type));
>  			if (type == NULL)
>  				goto out_free_member_name;
> -			member_name = sep + 1;
> -			sep = strchr(member_name, '.');
> -			if (!sep)
> +			member_name = sep_mutable + 1;
> +			sep_mutable = strchr(member_name, '.');
> +			if (!sep_mutable)
>  				break;
>  
>  		}
> @@ -2950,7 +2950,7 @@ static struct prototype *prototype__new(const char *expression)
>  
>  	strcpy(prototype->name, expression);
>  
> -	const char *name = prototype->name;
> +	char *name = prototype->name;
>  
>  	prototype->nr_args = 0;
>  
> @@ -2964,10 +2964,9 @@ static struct prototype *prototype__new(const char *expression)
>  	if (args_close == NULL)
>  		goto out_no_closing_parens;
>  
> +	*args_open++ = *args_close = '\0';
>  	char *args = args_open;
>  
> -	*args++ = *args_close = '\0';
> -
>  	while (isspace(*args))
>  		++args;
>  
> @@ -3114,7 +3113,7 @@ static int type__find_type_enum(struct type *type, struct cu *cu, const char *ty
>  		return type__add_type_enum(type, te, cu);
>  
>  	// Now look at a 'virtual enum', i.e. the concatenation of multiple enums
> -	char *sep = strchr(type_enum, '+');
> +	const char *sep = strchr(type_enum, '+');
>  
>  	if (!sep)
>  		return -1;
> @@ -3126,13 +3125,13 @@ static int type__find_type_enum(struct type *type, struct cu *cu, const char *ty
>  
>  	int ret = -1;
>  
> -	sep = type_enums + (sep - type_enum);
> +	char *sep_mutable = type_enums + (sep - type_enum);
> +	char *cur = type_enums;
>  
> -	type_enum = type_enums;
> -	*sep = '\0';
> +	*sep_mutable = '\0';
>  
>  	while (1) {
> -		te = cu__find_enumeration_by_name(cu, type_enum, NULL);
> +		te = cu__find_enumeration_by_name(cu, cur, NULL);
>  
>  		if (!te)
>  			goto out;
> @@ -3141,10 +3140,12 @@ static int type__find_type_enum(struct type *type, struct cu *cu, const char *ty
>  		if (ret)
>  			goto out;
>  
> -		if (sep == NULL)
> +		if (sep_mutable == NULL)
>  			break;
> -		type_enum = sep + 1;
> -		sep = strchr(type_enum, '+');
> +		cur = sep_mutable + 1;
> +		sep_mutable = strchr(cur, '+');
> +		if (sep_mutable)
> +			*sep_mutable = '\0';
>  	}
>  
>  	ret = 0;