Re: [PATCH dwarves] btf_encoder: dynamically allocate the vars array for percpu variables

[Jiri Olsa <olsajiri@gmail.com>]

On Fri, Mar 01, 2024 at 12:41:06PM +0000, Alan Maguire wrote:
> Use consistent method across allocating function and per-cpu variable
> representations, based around (re)allocating the arrays based on demand.
> This avoids issues where the number of per-CPU variables exceeds the
> hardcoded limit.
> 
> Reported-by: John Hubbard <jhubbard@nvidia.com>
> Suggested-by: Jiri Olsa <olsajiri@gmail.com>
> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
> Tested-by: John Hubbard <jhubbard@nvidia.com>

Acked/Tested-by: Jiri Olsa <jolsa@kernel.org>

thanks,
jirka

> ---
>  btf_encoder.c | 38 +++++++++++++++++++++++++++++---------
>  1 file changed, 29 insertions(+), 9 deletions(-)
> 
> diff --git a/btf_encoder.c b/btf_encoder.c
> index fd04008..a43d702 100644
> --- a/btf_encoder.c
> +++ b/btf_encoder.c
> @@ -50,8 +50,6 @@ struct elf_function {
>  	struct btf_encoder_state state;
>  };
>  
> -#define MAX_PERCPU_VAR_CNT 4096
> -
>  struct var_info {
>  	uint64_t    addr;
>  	const char *name;
> @@ -80,8 +78,9 @@ struct btf_encoder {
>  			  is_rel;
>  	uint32_t	  array_index_id;
>  	struct {
> -		struct var_info vars[MAX_PERCPU_VAR_CNT];
> +		struct var_info *vars;
>  		int		var_cnt;
> +		int		allocated;
>  		uint32_t	shndx;
>  		uint64_t	base_addr;
>  		uint64_t	sec_sz;
> @@ -983,6 +982,16 @@ static int functions_cmp(const void *_a, const void *_b)
>  #define max(x, y) ((x) < (y) ? (y) : (x))
>  #endif
>  
> +static void *reallocarray_grow(void *ptr, int *nmemb, size_t size)
> +{
> +	int new_nmemb = max(1000, *nmemb * 3 / 2);
> +	void *new = realloc(ptr, new_nmemb * size);
> +
> +	if (new)
> +		*nmemb = new_nmemb;
> +	return new;
> +}
> +
>  static int btf_encoder__collect_function(struct btf_encoder *encoder, GElf_Sym *sym)
>  {
>  	struct elf_function *new;
> @@ -995,8 +1004,9 @@ static int btf_encoder__collect_function(struct btf_encoder *encoder, GElf_Sym *
>  		return 0;
>  
>  	if (encoder->functions.cnt == encoder->functions.allocated) {
> -		encoder->functions.allocated = max(1000, encoder->functions.allocated * 3 / 2);
> -		new = realloc(encoder->functions.entries, encoder->functions.allocated * sizeof(*encoder->functions.entries));
> +		new = reallocarray_grow(encoder->functions.entries,
> +					&encoder->functions.allocated,
> +					sizeof(*encoder->functions.entries));
>  		if (!new) {
>  			/*
>  			 * The cleanup - delete_functions is called
> @@ -1439,10 +1449,17 @@ static int btf_encoder__collect_percpu_var(struct btf_encoder *encoder, GElf_Sym
>  	if (!encoder->is_rel)
>  		addr -= encoder->percpu.base_addr;
>  
> -	if (encoder->percpu.var_cnt == MAX_PERCPU_VAR_CNT) {
> -		fprintf(stderr, "Reached the limit of per-CPU variables: %d\n",
> -			MAX_PERCPU_VAR_CNT);
> -		return -1;
> +	if (encoder->percpu.var_cnt == encoder->percpu.allocated) {
> +		struct var_info *new;
> +
> +		new = reallocarray_grow(encoder->percpu.vars,
> +					&encoder->percpu.allocated,
> +					sizeof(*encoder->percpu.vars));
> +		if (!new) {
> +			fprintf(stderr, "Failed to allocate memory for variables\n");
> +			return -1;
> +		}
> +		encoder->percpu.vars = new;
>  	}
>  	encoder->percpu.vars[encoder->percpu.var_cnt].addr = addr;
>  	encoder->percpu.vars[encoder->percpu.var_cnt].sz = size;
> @@ -1720,6 +1737,9 @@ void btf_encoder__delete(struct btf_encoder *encoder)
>  	encoder->functions.allocated = encoder->functions.cnt = 0;
>  	free(encoder->functions.entries);
>  	encoder->functions.entries = NULL;
> +	encoder->percpu.allocated = encoder->percpu.var_cnt = 0;
> +	free(encoder->percpu.vars);
> +	encoder->percpu.vars = NULL;
>  
>  	free(encoder);
>  }
> -- 
> 2.39.3
>