Re: [PATCH] scripts/kallsyms: remove KSYM_NAME_LEN_BUFFER

[Nicolas Schier]

On Mon, Jun 05, 2023 at 09:26:04PM +0900, Masahiro Yamada wrote:
> You do not need to decide the buffer size statically.
> 
> Use getline() to grow the line buffer as needed.
> 
> Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
> ---
> 
>  scripts/kallsyms.c | 61 ++++++++++++++++++++++++----------------------
>  1 file changed, 32 insertions(+), 29 deletions(-)
> 
> diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
> index 0d2db41177b2..fc9709839b19 100644
> --- a/scripts/kallsyms.c
> +++ b/scripts/kallsyms.c
> @@ -19,6 +19,7 @@
>   *
>   */
>  
> +#include <errno.h>
>  #include <getopt.h>
>  #include <stdbool.h>
>  #include <stdio.h>
> @@ -29,24 +30,8 @@
>  
>  #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof(arr[0]))
>  
> -#define _stringify_1(x)	#x
> -#define _stringify(x)	_stringify_1(x)
> -
>  #define KSYM_NAME_LEN		512
>  
> -/*
> - * A substantially bigger size than the current maximum.
> - *
> - * It cannot be defined as an expression because it gets stringified
> - * for the fscanf() format string. Therefore, a _Static_assert() is
> - * used instead to maintain the relationship with KSYM_NAME_LEN.
> - */
> -#define KSYM_NAME_LEN_BUFFER	2048
> -_Static_assert(
> -	KSYM_NAME_LEN_BUFFER == KSYM_NAME_LEN * 4,
> -	"Please keep KSYM_NAME_LEN_BUFFER in sync with KSYM_NAME_LEN"
> -);
> -
>  struct sym_entry {
>  	unsigned long long addr;
>  	unsigned int len;
> @@ -136,24 +121,40 @@ static void check_symbol_range(const char *sym, unsigned long long addr,
>  	}
>  }
>  
> -static struct sym_entry *read_symbol(FILE *in)
> +static struct sym_entry *read_symbol(FILE *in, char **buf, size_t *buf_len)
>  {
> -	char name[KSYM_NAME_LEN_BUFFER+1], type;
> +	char *name, type, *p;
>  	unsigned long long addr;
> -	unsigned int len;
> +	size_t len;
> +	ssize_t readlen;
>  	struct sym_entry *sym;
> -	int rc;
>  
> -	rc = fscanf(in, "%llx %c %" _stringify(KSYM_NAME_LEN_BUFFER) "s\n", &addr, &type, name);
> -	if (rc != 3) {
> -		if (rc != EOF && fgets(name, ARRAY_SIZE(name), in) == NULL)
> -			fprintf(stderr, "Read error or end of file.\n");
> +	readlen = getline(buf, buf_len, in);
> +	if (readlen < 0) {
> +		if (errno) {
> +			perror("read_symbol");
> +			exit(EXIT_FAILURE);
> +		}
>  		return NULL;
>  	}
> -	if (strlen(name) >= KSYM_NAME_LEN) {
> +
> +	if ((*buf)[readlen - 1] == '\n')
> +		(*buf)[readlen - 1] = 0;
> +
> +	addr = strtoull(*buf, &p, 16);
> +
> +	if (*buf == p || *p++ != ' ' || !isascii((type = *p++)) || *p++ != ' ') {

For me, this is not as easy to read as the previous fscanf(), but I like
the switch to getline().

Reviewed-by: Nicolas Schier <n.schier@xxxxxx>

> +		fprintf(stderr, "line format error\n");
> +		exit(EXIT_FAILURE);
> +	}
> +
> +	name = p;
> +	len = strlen(name);
> +
> +	if (len >= KSYM_NAME_LEN) {
>  		fprintf(stderr, "Symbol %s too long for kallsyms (%zu >= %d).\n"
>  				"Please increase KSYM_NAME_LEN both in kernel and kallsyms.c\n",
> -			name, strlen(name), KSYM_NAME_LEN);
> +			name, len, KSYM_NAME_LEN);
>  		return NULL;
>  	}
>  
> @@ -169,8 +170,7 @@ static struct sym_entry *read_symbol(FILE *in)
>  
>  	/* include the type field in the symbol name, so that it gets
>  	 * compressed together */
> -
> -	len = strlen(name) + 1;
> +	len++;
>  
>  	sym = malloc(sizeof(*sym) + len + 1);
>  	if (!sym) {
> @@ -257,6 +257,8 @@ static void read_map(const char *in)
>  {
>  	FILE *fp;
>  	struct sym_entry *sym;
> +	char *buf = NULL;
> +	size_t buflen = 0;
>  
>  	fp = fopen(in, "r");
>  	if (!fp) {
> @@ -265,7 +267,7 @@ static void read_map(const char *in)
>  	}
>  
>  	while (!feof(fp)) {
> -		sym = read_symbol(fp);
> +		sym = read_symbol(fp, &buf, &buflen);
>  		if (!sym)
>  			continue;
>  
> @@ -284,6 +286,7 @@ static void read_map(const char *in)
>  		table[table_cnt++] = sym;
>  	}
>  
> +	free(buf);
>  	fclose(fp);
>  }
>  
> -- 
> 2.39.2
>