[PATCH v6 3/5] perf symbols: Point to the symbol name instead of embedding it

[Alireza Haghdoost via B4 Relay <devnull+haghdoost.uber.com@kernel.org>]

From: Alireza Haghdoost <haghdoost@uber.com>

This patch changes the type of the name field in struct symbol from a
flexible array (char name[]) to a pointer (char *name). It is a
refactoring and does not change behavior, but it adds 8 bytes to each
symbol allocation on 64-bit hosts.

The next patch creates symbols whose names are read only when they are
needed. When perf creates such a symbol, it does not know the length of
the name, so it cannot allocate space for the name after the symbol.
Perf also cannot allocate a larger symbol after it reads the name,
because the rb-tree and the callers keep pointers to the symbol. With a
pointer, perf can allocate the name separately and set the pointer later.

Signed-off-by: Alireza Haghdoost <haghdoost@uber.com>
---
 tools/perf/ui/stdio/hist.c | 1 +
 tools/perf/util/symbol.c   | 1 +
 tools/perf/util/symbol.h   | 2 +-
 3 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/perf/ui/stdio/hist.c b/tools/perf/ui/stdio/hist.c
index 8c4c8925df2c..c65e3aa73a13 100644
--- a/tools/perf/ui/stdio/hist.c
+++ b/tools/perf/ui/stdio/hist.c
@@ -106,6 +106,7 @@ static void init_rem_hits(void)
 		return;
 	}
 
+	rem_sq_bracket->name = (char *)(rem_sq_bracket + 1);
 	strcpy(rem_sq_bracket->name, "[...]");
 	rem_hits.ms.sym = rem_sq_bracket;
 }
diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index 2d611c05d000..02c077d7e2a6 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -362,6 +362,7 @@ struct symbol *symbol__new(u64 start, u64 len, u8 binding, u8 type, const char *
 
 	pr_debug4("%s: %s %#" PRIx64 "-%#" PRIx64 "\n",
 		  __func__, name, start, sym->end);
+	sym->name = (char *)(sym + 1);
 	memcpy(sym->name, name, namelen);
 
 	return sym;
diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
index d8386c4a7fc5..c231d8e4427c 100644
--- a/tools/perf/util/symbol.h
+++ b/tools/perf/util/symbol.h
@@ -95,7 +95,7 @@ struct symbol {
 	/** Architecture specific. Unused except on PPC where it holds st_other. */
 	u8		arch_sym;
 	/** The name of length namelen associated with the symbol. */
-	char		name[];
+	char		*name;
 };
 
 void symbol__delete(struct symbol *sym);

-- 
Git-157)