On 03/15, Ivan Vecera wrote:
> After some experiences I found that urandom_read does not need to be
> linked statically. When the 'read' syscall call is moved to separate
> non-inlined function then bpf_get_stackid() is able to find
> the executable in stack trace and extract its build_id from it.
But why? Do you have some problems with it being linked statically?
>
> Signed-off-by: Ivan Vecera <ivecera@xxxxxxxxxx>
> ---
> tools/testing/selftests/bpf/Makefile | 2 +-
> tools/testing/selftests/bpf/urandom_read.c | 15 +++++++++++----
> 2 files changed, 12 insertions(+), 5 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> index 2aed37ea61a4..c33900a8fec0 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -69,7 +69,7 @@ TEST_CUSTOM_PROGS = $(OUTPUT)/urandom_read
> all: $(TEST_CUSTOM_PROGS)
>
> $(OUTPUT)/urandom_read: $(OUTPUT)/%: %.c
> - $(CC) -o $@ -static $< -Wl,--build-id
> + $(CC) -o $@ $< -Wl,--build-id
>
> BPFOBJ := $(OUTPUT)/libbpf.a
>
> diff --git a/tools/testing/selftests/bpf/urandom_read.c b/tools/testing/selftests/bpf/urandom_read.c
> index 9de8b7cb4e6d..db781052758d 100644
> --- a/tools/testing/selftests/bpf/urandom_read.c
> +++ b/tools/testing/selftests/bpf/urandom_read.c
> @@ -7,11 +7,19 @@
>
> #define BUF_SIZE 256
>
> +static __attribute__((noinline))
> +void urandom_read(int fd, int count)
> +{
> + char buf[BUF_SIZE];
> + int i;
> +
> + for (i = 0; i < count; ++i)
> + read(fd, buf, BUF_SIZE);
> +}
> +
> int main(int argc, char *argv[])
> {
> int fd = open("/dev/urandom", O_RDONLY);
> - int i;
> - char buf[BUF_SIZE];
> int count = 4;
>
> if (fd < 0)
> @@ -20,8 +28,7 @@ int main(int argc, char *argv[])
> if (argc == 2)
> count = atoi(argv[1]);
>
> - for (i = 0; i < count; ++i)
> - read(fd, buf, BUF_SIZE);
> + urandom_read(fd, count);
>
> close(fd);
> return 0;
> --
> 2.19.2
>
