Re: [PATCH] arch, passt: Use executable link to form AVX2 binary path

[David Gibson <david@gibson.dropbear.id.au>]

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On Wed, Jul 13, 2022 at 08:17:09AM +0200, Stefano Brivio wrote:
> ...instead of argv[0], which might or might not contain a valid path
> to the executable itself. Instead of mangling argv[0], use the same
> link to find out if we're already running the AVX2 build where
> supported.

Ah.. yeah, I remember seeing that usage of argv[0] and suspecting it
might be a problem.

> Alternatively, we could use execvpe(), but that might result in
> running a different installed version, in case e.g. the set of
> binaries is present in both /usr/bin and /usr/local/bin, with both
> being in $PATH.
> 
> Reported-by: Wenli Quan <wquan(a)redhat.com>
> Link: https://bugzilla.redhat.com/show_bug.cgi?id=2101310
> Signed-off-by: Stefano Brivio <sbrivio(a)redhat.com>



> ---
>  arch.c  | 25 +++++++++++++++----------
>  passt.c |  9 ++++++---
>  2 files changed, 21 insertions(+), 13 deletions(-)
> 
> diff --git a/arch.c b/arch.c
> index ae21d59..71feda3 100644
> --- a/arch.c
> +++ b/arch.c
> @@ -14,26 +14,31 @@
>  
>  #include <limits.h>
>  #include <stdio.h>
> +#include <stdlib.h>
>  #include <string.h>
>  #include <unistd.h>
>  
>  /**
> - * arch_avx2_exec() - Run AVX2 build if supported, drop suffix from argv[0]
> + * arch_avx2_exec() - Switch to AVX2 build if supported
>   * @argv:	Arguments from command line
>   */
>  #ifdef __x86_64__
> -static char avx2_path[PATH_MAX];
> -
>  void arch_avx2_exec(char **argv)
>  {
> -	char *p = strstr(argv[0], ".avx2");
> +	char exe[PATH_MAX], new_path[PATH_MAX + sizeof(".avx2")], *p;
> +
> +	if (readlink("/proc/self/exe", exe, PATH_MAX) < 0) {
> +		perror("readlink /proc/self/exe");
> +		exit(EXIT_FAILURE);
> +	}
> +
> +	p = strstr(exe, ".avx2");
> +	if (p && strlen(p) == strlen(".avx2"))
> +		return;
>  
> -	if (p) {
> -		*p = 0;
> -	} else if (__builtin_cpu_supports("avx2")) {
> -		snprintf(avx2_path, PATH_MAX, "%s.avx2", argv[0]);
> -		argv[0] = avx2_path;
> -		execve(avx2_path, argv, environ);
> +	if (__builtin_cpu_supports("avx2")) {
> +		snprintf(new_path, PATH_MAX + sizeof(".avx2"), "%s.avx2", exe);
> +		execve(new_path, argv, environ);
>  		perror("Can't run AVX2 build, using non-AVX2 version");
>  	}
>  }
> diff --git a/passt.c b/passt.c
> index dd0229a..56fcf5f 100644
> --- a/passt.c
> +++ b/passt.c
> @@ -35,6 +35,7 @@
>  #include <sys/mount.h>
>  #include <netinet/ip.h>
>  #include <net/ethernet.h>
> +#include <libgen.h>
>  #include <stdlib.h>
>  #include <unistd.h>
>  #include <net/if.h>
> @@ -283,11 +284,11 @@ int main(int argc, char **argv)
>  {
>  	int nfds, i, devnull_fd = -1, pidfile_fd = -1, quit_fd;
>  	struct epoll_event events[EPOLL_EVENTS];
> +	char *log_name, argv0[PATH_MAX], *name;
>  	struct ctx c = { 0 };
>  	struct rlimit limit;
>  	struct timespec now;
>  	struct sigaction sa;
> -	char *log_name;
>  
>  	arch_avx2_exec(argv);
>  
> @@ -304,14 +305,16 @@ int main(int argc, char **argv)
>  	if (argc < 1)
>  		exit(EXIT_FAILURE);
>  
> -	if (strstr(argv[0], "pasta")) {
> +	strncpy(argv0, argv[0], PATH_MAX - 1);
> +	name = basename(argv0);
> +	if (strstr(name, "pasta")) {
>  		sa.sa_handler = pasta_child_handler;
>  		sigaction(SIGCHLD, &sa, NULL);
>  		signal(SIGPIPE, SIG_IGN);
>  
>  		c.mode = MODE_PASTA;
>  		log_name = "pasta";
> -	} else if (strstr(argv[0], "passt")) {
> +	} else if (strstr(name, "passt")) {
>  		c.mode = MODE_PASST;
>  		log_name = "passt";
>  	} else {

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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