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.
Signed-off-by: Ivan Vecera <[email protected]>
---
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
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 <[email protected]>
> ---
> 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
>
On 15. 03. 19 21:08, Stanislav Fomichev wrote:
> 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?
>
Dependency... you don't need to install static glibc to compile the bpf samples.
Shared libc is available everytime.
Ivan
On 03/15, Ivan Vecera wrote:
> On 15. 03. 19 21:08, Stanislav Fomichev wrote:
> > 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?
> >
> Dependency... you don't need to install static glibc to compile the bpf
> samples. Shared libc is available everytime.
Oh, the distros that do -devel _and_ -static packages :-)
So your patch essentially adds a call, that leaves a trace on the stack
with our build-id. I guess that works as well.
>
> Ivan
----- Stanislav Fomichev <[email protected]> wrote:
> On 03/15, Ivan Vecera wrote:
> > On 15. 03. 19 21:08, Stanislav Fomichev wrote:
> > > 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?
> > >
> > Dependency... you don't need to install static glibc to compile the bpf
> > samples. Shared libc is available everytime.
> Oh, the distros that do -devel _and_ -static packages :-)
>
> So your patch essentially adds a call, that leaves a trace on the stack
> with our build-id. I guess that works as well.
Without that additional call this does not work and build_id selftest fails.
I.
On 03/15, Ivan Vecera wrote:
>
> ----- Stanislav Fomichev <[email protected]> wrote:
> > On 03/15, Ivan Vecera wrote:
> > > On 15. 03. 19 21:08, Stanislav Fomichev wrote:
> > > > 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?
> > > >
> > > Dependency... you don't need to install static glibc to compile the bpf
> > > samples. Shared libc is available everytime.
> > Oh, the distros that do -devel _and_ -static packages :-)
> >
> > So your patch essentially adds a call, that leaves a trace on the stack
> > with our build-id. I guess that works as well.
>
> Without that additional call this does not work and build_id selftest fails.
Oh, yeah, I was just trying to clarify why it fails without -static and why
your patch makes it work for non-static :-)
You can put more details in the commit message; you'd have to resubmit
whenever net-next/bpf-next opens anyway.
>
> I.
On Fri, Mar 15, 2019 at 1:04 PM Ivan Vecera <[email protected]> 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.
>
> Signed-off-by: Ivan Vecera <[email protected]>
Applied. Thanks