[PATCH] perf disasm powerpc: handle Power10 prefixed instruction continuation lines

Power10 introduces prefixed instructions that are 8 bytes wide.  objdump
emits these as two lines: the first carries both the raw bytes and the
mnemonic, while the second carries only the raw bytes of the second word
with no mnemonic:

  1020900c:  0b 00 10 06  pla  r31,757280  # 102c1e2c <cctki_vi_ML_CCZ4>
  10209010:  20 8e e0 3b

disasm_line__parse_powerpc() calls disasm_line__parse() on the mnemonic
portion of the line.  disasm_line__parse() returns -1 when the name
string is empty, which causes disasm_line__new() to return NULL, which
causes symbol__parse_objdump_line() to return -1, which immediately
breaks the objdump output parsing loop in symbol__disassemble_objdump().

The result is that annotation of any function containing a prefixed
instruction stops at the continuation word and all subsequent
instructions in the function are lost.

Fix this by treating an empty mnemonic as a valid case in
disasm_line__parse_powerpc(): skip the call to disasm_line__parse() and
set the instruction name to an empty heap-allocated string instead,
allowing parsing to continue to the next line.

Reported-by: Narendra Nalli <redacted>
Reported-by: Vijay Puliyala <redacted>
Signed-off-by: Athira Rajeev <redacted>
---
 tools/perf/util/disasm.c | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/disasm.c b/tools/perf/util/disasm.c
index e263a2a8715d..8dca703a5c74 100644
--- a/tools/perf/util/disasm.c
+++ b/tools/perf/util/disasm.c

@@ -884,10 +884,24 @@ static int disasm_line__parse_powerpc(struct disasm_line *dl, struct annotate_ar
 	if (name_raw_insn[0] == '\0')
 		return -1;
 
-	if (disasm)
-		ret = disasm_line__parse(name, namep, rawp);
-	else
+	if (disasm) {
+		/*
+		 * Power10 prefixed instructions are 8 bytes and objdump emits
+		 * the second word on its own line with raw bytes but no
+		 * mnemonic, e.g.:
+		 *   1020900c:  0b 00 10 06  pla  r31,757280
+		 *   10209010:  20 8e e0 3b
+		 *
+		 * Treat a missing mnemonic as an empty instruction name rather
+		 * than a parse failure, so that parsing continues past it.
+		 */
+		if (name[0] != '\0')
+			ret = disasm_line__parse(name, namep, rawp);
+		else
+			*namep = strdup("");
+	} else {
 		*namep = "";
+	}
 
 	tmp_raw_insn = strndup(name_raw_insn, 11);
 	if (tmp_raw_insn == NULL)

-- 
2.43.0