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(64-bit) and last 4 bytes(32-bit)
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 8/4 bytes from JITed buffers
before supplying them for disassembly.

Signed-off-by: Abhishek Dubey <redacted>
---
  .../selftests/bpf/jit_disasm_helpers.c        | 21 ++++++++++++++++++-
  1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/jit_disasm_helpers.c b/tools/testing/selftests/bpf/jit_disasm_helpers.c
index 3558fe10e28c..759d6a86803c 100644
--- a/tools/testing/selftests/bpf/jit_disasm_helpers.c
+++ b/tools/testing/selftests/bpf/jit_disasm_helpers.c

@@ -179,9 +179,11 @@ 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) {

@@ -225,9 +227,26 @@ 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 on 64-bit and last 4 bytes on 32-bit powerpc,
+	 * which can't disassemble to a valid instruction.
+	 */
+	triple = LLVMGetDefaultTargetTriple();
+	if (triple) {
+		if (strstr(triple, "powerpc64") || strstr(triple, "ppc64"))
+			trunc_len = 8;
+		else if (strstr(triple, "powerpc") || strstr(triple, "ppc"))
+			trunc_len = 4;
+		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]);