On Mon, Apr 4, 2022 at 3:29 AM Ilya Leoshkevich <iii@xxxxxxxxxxxxx> wrote:
>
> attach_probe selftest fails on Debian-based distros with `failed to
> resolve full path for 'libc.so.6'`. The reason is that these distros
> embraced multiarch to the point where even for the "main" architecture
> they store libc in /lib/<triple>.
>
> This is configured in /etc/ld.so.conf and in theory it's possible to
> replicate the loader's parsing and processing logic in libbpf, however
> a much simpler solution is to just enumerate the known library paths.
>
> Signed-off-by: Ilya Leoshkevich <iii@xxxxxxxxxxxxx>
> ---
> tools/lib/bpf/libbpf.c | 54 ++++++++++++++++++++++++++++++++++++------
> 1 file changed, 47 insertions(+), 7 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 6d2be53e4ba9..4f616b11564f 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -10707,21 +10707,61 @@ static long elf_find_func_offset(const char *binary_path, const char *name)
> return ret;
> }
>
> +static void add_debian_library_paths(const char **search_paths, int *n)
> +{
> + /*
> + * Based on https://packages.debian.org/sid/libc6.
> + *
> + * Assume that the traced program is built for the same architecture
> + * as libbpf, which should cover the vast majority of cases.
> + */
> +#if defined(__x86_64__)
> + search_paths[(*n)++] = "/lib/x86_64-linux-gnu";
> +#elif defined(__i386__)
> + search_paths[(*n)++] = "/lib/i386-linux-gnu";
> +#elif defined(__s390x__)
> + search_paths[(*n)++] = "/lib/s390x-linux-gnu";
> +#elif defined(__s390__)
> + search_paths[(*n)++] = "/lib/s390-linux-gnu";
> +#elif defined(__arm__)
> +#if defined(__SOFTFP__)
> + search_paths[(*n)++] = "/lib/arm-linux-gnueabi";
> +#else
> + search_paths[(*n)++] = "/lib/arm-linux-gnueabihf";
> +#endif /* defined(__SOFTFP__) */
> +#elif defined(__aarch64__)
> + search_paths[(*n)++] = "/lib/aarch64-linux-gnu";
> +#elif defined(__mips__) && (__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__)
> +#if _MIPS_SZLONG == 64
> + search_paths[(*n)++] = "/lib/mips64el-linux-gnuabi64";
> +#elif _MIPS_SZLONG == 32
> + search_paths[(*n)++] = "/lib/mipsel-linux-gnu";
> +#endif
> +#elif defined(__powerpc__) && (__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__)
> + search_paths[(*n)++] = "/lib/powerpc64le-linux-gnu";
> +#elif defined(__sparc__)
> + search_paths[(*n)++] = "/lib/sparc64-linux-gnu";
> +#elif defined(__riscv) && __riscv_xlen == 64
> + search_paths[(*n)++] = "/lib/riscv64-linux-gnu";
> +#endif
> +}
> +
that's pretty comprehensive :)
But let's make this function return const char * instead, with NULL
for unknown/unsupported architectures. This will make the below code
simpler....
> /* Get full path to program/shared library. */
> static int resolve_full_path(const char *file, char *result, size_t result_sz)
> {
> - const char *search_paths[2];
> - int i;
> + const char *search_paths[3];
> + int i, n = 0;
>
instead of counting, we can just NULL-initialize search_paths and
teach the loop below to ignore NULL entries?
> if (strstr(file, ".so")) {
> - search_paths[0] = getenv("LD_LIBRARY_PATH");
> - search_paths[1] = "/usr/lib64:/usr/lib";
> + search_paths[n++] = getenv("LD_LIBRARY_PATH");
> + search_paths[n++] = "/usr/lib64:/usr/lib";
> + add_debian_library_paths(search_paths, &n);
so you'll just have
search_paths[2] = arch_specific_lib_paths();
> } else {
> - search_paths[0] = getenv("PATH");
> - search_paths[1] = "/usr/bin:/usr/sbin";
> + search_paths[n++] = getenv("PATH");
> + search_paths[n++] = "/usr/bin:/usr/sbin";
> }
>
> - for (i = 0; i < ARRAY_SIZE(search_paths); i++) {
> + for (i = 0; i < n; i++) {
> const char *s;
>
> if (!search_paths[i])
oh, actually we already do ignore NULLs, it seems?
> --
> 2.35.1
>
