[PATCH v5 3/6] selftest/bpf: Fixing powerpc JIT disassembly failure
From: <hidden>
Date: 2026-05-19 19:38:25
Also in:
bpf, linux-kselftest, stable
Subsystem:
bpf [general] (safe dynamic programs and tools), bpf [selftests] (test runners & infrastructure), kernel selftest framework, the rest · Maintainers:
Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, Shuah Khan, Linus Torvalds
From: Abhishek Dubey <redacted> Ensure that the trampoline stubs JITed at the tail of the epilogue do not expose the dummy trampoline address stored in the last 8 bytes (for both 64-bit and 32-bit PowerPC) to the disassembly flow. Prevent the disassembler from ingesting this memory address, as it may occasionally decode into a seemingly valid but incorrect instruction. Fix this issue by truncating the last 8 bytes from JITed buffers before supplying them for disassembly. Signed-off-by: Abhishek Dubey <redacted> --- tools/testing/selftests/bpf/jit_disasm_helpers.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-)
diff --git a/tools/testing/selftests/bpf/jit_disasm_helpers.c b/tools/testing/selftests/bpf/jit_disasm_helpers.c
index 364c557c5115..9e6613479145 100644
--- a/tools/testing/selftests/bpf/jit_disasm_helpers.c
+++ b/tools/testing/selftests/bpf/jit_disasm_helpers.c@@ -170,9 +170,11 @@ int get_jited_program_text(int fd, char *text, size_t text_sz) struct bpf_prog_info info = {}; __u32 info_len = sizeof(info); __u32 jited_funcs, len, pc; + __u32 trunc_len = 0; __u32 *func_lens = NULL; FILE *text_out = NULL; uint8_t *image = NULL; + char *triple = NULL; int i, err = 0; if (!llvm_initialized) {
@@ -216,9 +218,21 @@ int get_jited_program_text(int fd, char *text, size_t text_sz) if (!ASSERT_OK(err, "bpf_prog_get_info_by_fd #2")) goto out; + /* + * last 8 bytes contains dummy_trampoline address in JIT + * output for 64-bit and 32-bit powerpc, which can't + * disassemble a to valid instruction. + */ + triple = LLVMGetDefaultTargetTriple(); + if (triple) { + if (strstr(triple, "powerpc")) + trunc_len = 8; + LLVMDisposeMessage(triple); + } + for (pc = 0, i = 0; i < jited_funcs; ++i) { fprintf(text_out, "func #%d:\n", i); - disasm_one_func(text_out, image + pc, func_lens[i]); + disasm_one_func(text_out, image + pc, func_lens[i] - trunc_len); fprintf(text_out, "\n"); pc += func_lens[i]; }
--
2.52.0