Re: [PATCH bpf-next v2 3/3] selftests/bpf: Add tests for symbol versioning for uprobe

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On 05/09/2023 16:12, Hengqi Chen wrote:
> This exercises the newly added dynsym symbol versioning logics.
> Now we accept symbols in form of func, func@LIB_VERSION or
> func@@LIB_VERSION.
> 
> The test rely on liburandom_read.so. For liburandom_read.so, we have:
> 
>     $ nm -D liburandom_read.so
>                      w __cxa_finalize@GLIBC_2.17
>                      w __gmon_start__
>                      w _ITM_deregisterTMCloneTable
>                      w _ITM_registerTMCloneTable
>     0000000000000000 A LIBURANDOM_READ_1.0.0
>     0000000000000000 A LIBURANDOM_READ_2.0.0
>     000000000000081c T urandlib_api@@LIBURANDOM_READ_2.0.0
>     0000000000000814 T urandlib_api@LIBURANDOM_READ_1.0.0
>     0000000000000824 T urandlib_api_sameoffset@LIBURANDOM_READ_1.0.0
>     0000000000000824 T urandlib_api_sameoffset@@LIBURANDOM_READ_2.0.0
>     000000000000082c T urandlib_read_without_sema@@LIBURANDOM_READ_1.0.0
>     00000000000007c4 T urandlib_read_with_sema@@LIBURANDOM_READ_1.0.0
>     0000000000011018 D urandlib_read_with_sema_semaphore@@LIBURANDOM_READ_1.0.0
> 
> For `urandlib_api`, specifying `urandlib_api` will cause a conflict because
> there are two symbols named urandlib_api and both are global bind.
> For `urandlib_api_sameoffset`, there are also two symbols in the .so, but
> both are at the same offset and essentially they refer to the same function
> so no conflict.
> 
> Signed-off-by: Hengqi Chen <hengqi.chen@xxxxxxxxx>

Great work putting tests together for this! One small suggestion if
there's a v3; would it be worth having a uretprobe test that uses
library version specification too?

Reviewed-by: Alan Maguire <alan.maguire@xxxxxxxxxx>


> ---
>  tools/testing/selftests/bpf/Makefile          |  5 +-
>  .../testing/selftests/bpf/liburandom_read.map | 15 +++
>  .../testing/selftests/bpf/prog_tests/uprobe.c | 95 +++++++++++++++++++
>  .../testing/selftests/bpf/progs/test_uprobe.c | 61 ++++++++++++
>  tools/testing/selftests/bpf/urandom_read.c    |  9 ++
>  .../testing/selftests/bpf/urandom_read_lib1.c | 41 ++++++++
>  6 files changed, 224 insertions(+), 2 deletions(-)
>  create mode 100644 tools/testing/selftests/bpf/liburandom_read.map
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/uprobe.c
>  create mode 100644 tools/testing/selftests/bpf/progs/test_uprobe.c
> 
> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> index edef49fcd23e..49ff9c716b79 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -193,11 +193,12 @@ endif
> 
>  # Filter out -static for liburandom_read.so and its dependent targets so that static builds
>  # do not fail. Static builds leave urandom_read relying on system-wide shared libraries.
> -$(OUTPUT)/liburandom_read.so: urandom_read_lib1.c urandom_read_lib2.c
> +$(OUTPUT)/liburandom_read.so: urandom_read_lib1.c urandom_read_lib2.c liburandom_read.map
>  	$(call msg,LIB,,$@)
>  	$(Q)$(CLANG) $(filter-out -static,$(CFLAGS) $(LDFLAGS))   \
> -		     $^ $(filter-out -static,$(LDLIBS))	     \
> +		     $(filter %.c,$^) $(filter-out -static,$(LDLIBS)) \
>  		     -fuse-ld=$(LLD) -Wl,-znoseparate-code -Wl,--build-id=sha1 \
> +		     -Wl,--version-script=liburandom_read.map \
>  		     -fPIC -shared -o $@
> 
>  $(OUTPUT)/urandom_read: urandom_read.c urandom_read_aux.c $(OUTPUT)/liburandom_read.so
> diff --git a/tools/testing/selftests/bpf/liburandom_read.map b/tools/testing/selftests/bpf/liburandom_read.map
> new file mode 100644
> index 000000000000..38a97a419a04
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/liburandom_read.map
> @@ -0,0 +1,15 @@
> +LIBURANDOM_READ_1.0.0 {
> +	global:
> +		urandlib_api;
> +		urandlib_api_sameoffset;
> +		urandlib_read_without_sema;
> +		urandlib_read_with_sema;
> +		urandlib_read_with_sema_semaphore;
> +	local:
> +		*;
> +};
> +
> +LIBURANDOM_READ_2.0.0 {
> +	global:
> +		urandlib_api;
> +} LIBURANDOM_READ_1.0.0;
> diff --git a/tools/testing/selftests/bpf/prog_tests/uprobe.c b/tools/testing/selftests/bpf/prog_tests/uprobe.c
> new file mode 100644
> index 000000000000..6c619bcca41c
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/uprobe.c
> @@ -0,0 +1,95 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2021 Hengqi Chen */
> +
> +#include <test_progs.h>
> +#include "test_uprobe.skel.h"
> +
> +static FILE *urand_spawn(int *pid)
> +{
> +	FILE *f;
> +
> +	/* urandom_read's stdout is wired into f */
> +	f = popen("./urandom_read 1 report-pid", "r");
> +	if (!f)
> +		return NULL;
> +
> +	if (fscanf(f, "%d", pid) != 1) {
> +		pclose(f);
> +		errno = EINVAL;
> +		return NULL;
> +	}
> +
> +	return f;
> +}
> +
> +static int urand_trigger(FILE **urand_pipe)
> +{
> +	int exit_code;
> +
> +	/* pclose() waits for child process to exit and returns their exit code */
> +	exit_code = pclose(*urand_pipe);
> +	*urand_pipe = NULL;
> +
> +	return exit_code;
> +}
> +
> +void test_uprobe(void)
> +{
> +	LIBBPF_OPTS(bpf_uprobe_opts, uprobe_opts);
> +	struct test_uprobe *skel;
> +	FILE *urand_pipe = NULL;
> +	int urand_pid = 0, err;
> +
> +	skel = test_uprobe__open_and_load();
> +	if (!ASSERT_OK_PTR(skel, "skel_open"))
> +		return;
> +
> +	urand_pipe = urand_spawn(&urand_pid);
> +	if (!ASSERT_OK_PTR(urand_pipe, "urand_spawn"))
> +		goto cleanup;
> +
> +	skel->bss->my_pid = urand_pid;
> +
> +	/* Manual attach uprobe to urandlib_api
> +	 * There are two `urandlib_api` symbols in .dynsym section:
> +	 *   - urandlib_api@LIBURANDOM_READ_1.0.0
> +	 *   - urandlib_api@LIBURANDOM_READ_1.0.0
> +	 * Both are global bind and would cause a conflict if user
> +	 * specify the symbol name without a version suffix
> +	 */
> +	uprobe_opts.func_name = "urandlib_api";
> +	skel->links.test4 = bpf_program__attach_uprobe_opts(skel->progs.test4,
> +							    urand_pid,
> +							    "./liburandom_read.so",
> +							    0 /* offset */,
> +							    &uprobe_opts);
> +	if (!ASSERT_ERR_PTR(skel->links.test4, "urandlib_api_attach_conflict"))
> +		goto cleanup;
> +
> +	uprobe_opts.func_name = "urandlib_api@LIBURANDOM_READ_1.0.0";
> +	skel->links.test4 = bpf_program__attach_uprobe_opts(skel->progs.test4,
> +							    urand_pid,
> +							    "./liburandom_read.so",
> +							    0 /* offset */,
> +							    &uprobe_opts);
> +	if (!ASSERT_OK_PTR(skel->links.test4, "urandlib_api_attach_ok"))
> +		goto cleanup;
> +
> +	/* Auto attach 3 uprobes to urandlib_api_sameoffset */
> +	err = test_uprobe__attach(skel);
> +	if (!ASSERT_OK(err, "skel_attach"))
> +		goto cleanup;
> +
> +	/* trigger urandom_read */
> +	ASSERT_OK(urand_trigger(&urand_pipe), "urand_exit_code");
> +
> +	ASSERT_EQ(skel->bss->test1_result, 1, "urandlib_api_sameoffset");
> +	ASSERT_EQ(skel->bss->test2_result, 1, "urandlib_api_sameoffset@v1");
> +	ASSERT_EQ(skel->bss->test3_result, 1, "urandlib_api_sameoffset@@v2");
> +	ASSERT_EQ(skel->bss->test4_result, 1, "urandlib_api");
> +
> +cleanup:
> +	if (urand_pipe)
> +		pclose(urand_pipe);
> +	test_uprobe__destroy(skel);
> +}
> diff --git a/tools/testing/selftests/bpf/progs/test_uprobe.c b/tools/testing/selftests/bpf/progs/test_uprobe.c
> new file mode 100644
> index 000000000000..8680280558da
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/test_uprobe.c
> @@ -0,0 +1,61 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2023 Hengqi Chen */
> +
> +#include "vmlinux.h"
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +
> +pid_t my_pid = 0;
> +
> +int test1_result = 0;
> +int test2_result = 0;
> +int test3_result = 0;
> +int test4_result = 0;
> +
> +SEC("uprobe/./liburandom_read.so:urandlib_api_sameoffset")
> +int BPF_UPROBE(test1)
> +{
> +	pid_t pid = bpf_get_current_pid_tgid() >> 32;
> +
> +	if (pid != my_pid)
> +		return 0;
> +
> +	test1_result = 1;
> +	return 0;
> +}
> +
> +SEC("uprobe/./liburandom_read.so:urandlib_api_sameoffset@LIBURANDOM_READ_1.0.0")
> +int BPF_UPROBE(test2)
> +{
> +	pid_t pid = bpf_get_current_pid_tgid() >> 32;
> +
> +	if (pid != my_pid)
> +		return 0;
> +
> +	test2_result = 1;
> +	return 0;
> +}
> +
> +SEC("uprobe/./liburandom_read.so:urandlib_api_sameoffset@@LIBURANDOM_READ_2.0.0")
> +int BPF_UPROBE(test3)
> +{
> +	pid_t pid = bpf_get_current_pid_tgid() >> 32;
> +
> +	if (pid != my_pid)
> +		return 0;
> +
> +	test3_result = 1;
> +	return 0;
> +}
> +
> +SEC("uprobe")
> +int BPF_UPROBE(test4)
> +{
> +	pid_t pid = bpf_get_current_pid_tgid() >> 32;
> +
> +	if (pid != my_pid)
> +		return 0;
> +
> +	test4_result = 1;
> +	return 0;
> +}
> diff --git a/tools/testing/selftests/bpf/urandom_read.c b/tools/testing/selftests/bpf/urandom_read.c
> index e92644d0fa75..b28e910a8fbb 100644
> --- a/tools/testing/selftests/bpf/urandom_read.c
> +++ b/tools/testing/selftests/bpf/urandom_read.c
> @@ -21,6 +21,11 @@ void urand_read_without_sema(int iter_num, int iter_cnt, int read_sz);
>  void urandlib_read_with_sema(int iter_num, int iter_cnt, int read_sz);
>  void urandlib_read_without_sema(int iter_num, int iter_cnt, int read_sz);
> 
> +int urandlib_api(void);
> +__asm__(".symver urandlib_api_old,urandlib_api@LIBURANDOM_READ_1.0.0");
> +int urandlib_api_old(void);
> +int urandlib_api_sameoffset(void);
> +
>  unsigned short urand_read_with_sema_semaphore SEC(".probes");
> 
>  static __attribute__((noinline))
> @@ -83,6 +88,10 @@ int main(int argc, char *argv[])
> 
>  	urandom_read(fd, count);
> 
> +	urandlib_api();
> +	urandlib_api_old();
> +	urandlib_api_sameoffset();
> +
>  	close(fd);
>  	return 0;
>  }
> diff --git a/tools/testing/selftests/bpf/urandom_read_lib1.c b/tools/testing/selftests/bpf/urandom_read_lib1.c
> index 86186e24b740..403b0735e223 100644
> --- a/tools/testing/selftests/bpf/urandom_read_lib1.c
> +++ b/tools/testing/selftests/bpf/urandom_read_lib1.c
> @@ -11,3 +11,44 @@ void urandlib_read_with_sema(int iter_num, int iter_cnt, int read_sz)
>  {
>  	STAP_PROBE3(urandlib, read_with_sema, iter_num, iter_cnt, read_sz);
>  }
> +
> +/* Symbol versioning is different between static and shared library.
> + * Properly versioned symbols are needed for shared library, but
> + * only the symbol of the new version is needed for static library.
> + * Starting with GNU C 10, use symver attribute instead of .symver assembler
> + * directive, which works better with GCC LTO builds.
> + */
> +#if defined(__GNUC__) && __GNUC__ >= 10
> +
> +#define DEFAULT_VERSION(internal_name, api_name, version) \
> +	__attribute__((symver(#api_name "@@" #version)))
> +#define COMPAT_VERSION(internal_name, api_name, version) \
> +	__attribute__((symver(#api_name "@" #version)))
> +
> +#else
> +
> +#define COMPAT_VERSION(internal_name, api_name, version) \
> +	asm(".symver " #internal_name "," #api_name "@" #version);
> +#define DEFAULT_VERSION(internal_name, api_name, version) \
> +	asm(".symver " #internal_name "," #api_name "@@" #version);
> +
> +#endif
> +
> +COMPAT_VERSION(urandlib_api_v1, urandlib_api, LIBURANDOM_READ_1.0.0)
> +int urandlib_api_v1(void)
> +{
> +	return 1;
> +}
> +
> +DEFAULT_VERSION(urandlib_api_v2, urandlib_api, LIBURANDOM_READ_2.0.0)
> +int urandlib_api_v2(void)
> +{
> +	return 2;
> +}
> +
> +COMPAT_VERSION(urandlib_api_sameoffset, urandlib_api_sameoffset, LIBURANDOM_READ_1.0.0)
> +DEFAULT_VERSION(urandlib_api_sameoffset, urandlib_api_sameoffset, LIBURANDOM_READ_2.0.0)
> +int urandlib_api_sameoffset(void)
> +{
> +	return 3;
> +}
> --
> 2.34.1




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