6.11-stable review patch. If anyone has any objections, please let me know.
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From: Eduard Zingerman eddyz87@gmail.com
[ Upstream commit 5bf1557e3d6a69113649d831276ea2f97585fc33 ]
test_progs uses glibc specific functions backtrace() and backtrace_symbols_fd() to print backtrace in case of SIGSEGV.
Recent commit (see fixes) updated test_progs.c to define stub versions of the same functions with attriubte "weak" in order to allow linking test_progs against musl libc. Unfortunately this broke the backtrace handling for glibc builds.
As it turns out, glibc defines backtrace() and backtrace_symbols_fd() as weak:
$ llvm-readelf --symbols /lib64/libc.so.6 \ | grep -P '( backtrace_symbols_fd| backtrace)$' 4910: 0000000000126b40 161 FUNC WEAK DEFAULT 16 backtrace 6843: 0000000000126f90 852 FUNC WEAK DEFAULT 16 backtrace_symbols_fd
So does test_progs:
$ llvm-readelf --symbols test_progs \ | grep -P '( backtrace_symbols_fd| backtrace)$' 2891: 00000000006ad190 15 FUNC WEAK DEFAULT 13 backtrace 11215: 00000000006ad1a0 41 FUNC WEAK DEFAULT 13 backtrace_symbols_fd
In such situation dynamic linker is not obliged to favour glibc implementation over the one defined in test_progs.
Compiling with the following simple modification to test_progs.c demonstrates the issue:
$ git diff ... --- a/tools/testing/selftests/bpf/test_progs.c +++ b/tools/testing/selftests/bpf/test_progs.c @@ -1817,6 +1817,7 @@ int main(int argc, char **argv) if (err) return err;
+ *(int *)0xdeadbeef = 42; err = cd_flavor_subdir(argv[0]); if (err) return err;
$ ./test_progs [0]: Caught signal #11! Stack trace: <backtrace not supported> Segmentation fault (core dumped)
Resolve this by hiding stub definitions behind __GLIBC__ macro check instead of using "weak" attribute.
Fixes: c9a83e76b5a9 ("selftests/bpf: Fix compile if backtrace support missing in libc") Signed-off-by: Eduard Zingerman eddyz87@gmail.com Signed-off-by: Andrii Nakryiko andrii@kernel.org Tested-by: Tony Ambardar tony.ambardar@gmail.com Reviewed-by: Tony Ambardar tony.ambardar@gmail.com Acked-by: Daniel Xu dxu@dxuuu.xyz Link: https://lore.kernel.org/bpf/20241003210307.3847907-1-eddyz87@gmail.com Signed-off-by: Sasha Levin sashal@kernel.org --- tools/testing/selftests/bpf/test_progs.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/tools/testing/selftests/bpf/test_progs.c b/tools/testing/selftests/bpf/test_progs.c index 05bd298b15f4c..080e4fd012d3d 100644 --- a/tools/testing/selftests/bpf/test_progs.c +++ b/tools/testing/selftests/bpf/test_progs.c @@ -20,11 +20,13 @@
#include "network_helpers.h"
+/* backtrace() and backtrace_symbols_fd() are glibc specific, + * use header file when glibc is available and provide stub + * implementations when another libc implementation is used. + */ #ifdef __GLIBC__ #include <execinfo.h> /* backtrace */ -#endif - -/* Default backtrace funcs if missing at link */ +#else __weak int backtrace(void **buffer, int size) { return 0; @@ -34,6 +36,7 @@ __weak void backtrace_symbols_fd(void *const *buffer, int size, int fd) { dprintf(fd, "<backtrace not supported>\n"); } +#endif /*__GLIBC__ */
static bool verbose(void) {