Re: [PATCH v2 bpf-next 10/10] selftests/bpf: add build ID tests

[Jiri Olsa <olsajiri@gmail.com>]

On Wed, Jul 24, 2024 at 03:52:10PM -0700, Andrii Nakryiko wrote:

SNIP

> +extern char build_id_start[];
> +extern char build_id_end[];
> +
> +int __attribute__((weak)) trigger_uprobe(bool build_id_resident)
> +{
> +	int page_sz = sysconf(_SC_PAGESIZE);
> +	void *addr;
> +
> +	/* page-align build ID start */
> +	addr = (void *)((uintptr_t)&build_id_start & ~(page_sz - 1));
> +
> +	/* to guarantee MADV_PAGEOUT work reliably, we need to ensure that
> +	 * memory range is mapped into current process, so we unconditionally
> +	 * do MADV_POPULATE_READ, and then MADV_PAGEOUT, if necessary
> +	 */
> +	madvise(addr, page_sz, MADV_POPULATE_READ);
> +	if (!build_id_resident)
> +		madvise(addr, page_sz, MADV_PAGEOUT);

could this fail? should we at least print the error,
might be tricky to display that becase it's called through system() ?

jirka

> +
> +	(void)uprobe();
> +
> +	return 0;
> +}
> +
>  int main(int argc, char **argv)
>  {
>  	if (argc != 2)
> @@ -84,6 +121,10 @@ int main(int argc, char **argv)
>  		return bench();
>  	if (!strcmp("usdt", argv[1]))
>  		return usdt();
> +	if (!strcmp("uprobe-paged-out", argv[1]))
> +		return trigger_uprobe(false /* page-out build ID */);
> +	if (!strcmp("uprobe-paged-in", argv[1]))
> +		return trigger_uprobe(true /* page-in build ID */);
>  
>  error:
>  	fprintf(stderr, "usage: %s <bench|usdt>\n", argv[0]);
> diff --git a/tools/testing/selftests/bpf/uprobe_multi.ld b/tools/testing/selftests/bpf/uprobe_multi.ld
> new file mode 100644
> index 000000000000..a2e94828bc8c
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/uprobe_multi.ld
> @@ -0,0 +1,11 @@
> +SECTIONS
> +{
> +	. = ALIGN(4096);
> +	.note.gnu.build-id : { *(.note.gnu.build-id) }
> +	. = ALIGN(4096);
> +}
> +INSERT AFTER .text;
> +
> +build_id_start = ADDR(.note.gnu.build-id);
> +build_id_end = ADDR(.note.gnu.build-id) + SIZEOF(.note.gnu.build-id);
> +
> -- 
> 2.43.0
> 
>