objtool/klp: fix mkstemp() failure with long paths

The elf_create_file() function fails with EINVAL when the build directory
path is long enough to truncate the "XXXXXX" suffix in the 256-byte
tmp_name buffer.

Simplify the code to remove the unnecessary dirname()/basename() split
and concatenation.  Instead, allocate the exact number of bytes needed for
the path.

Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
Link: https://patch.msgid.link/20260310203751.1479229-3-joe.lawrence@redhat.com
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

Author: joe-lawrence

tools/objtool/elf.c

@@ -16,7 +16,6 @@
 #include <string.h>
 #include <unistd.h>
 #include <errno.h>
-#include <libgen.h>
 #include <ctype.h>
 #include <linux/align.h>
 #include <linux/kernel.h>
@@ -1189,7 +1188,7 @@ struct elf *elf_open_read(const char *name, int flags)
 struct elf *elf_create_file(GElf_Ehdr *ehdr, const char *name)
 {
 	struct section *null, *symtab, *strtab, *shstrtab;
-	char *dir, *base, *tmp_name;
+	char *tmp_name;
 	struct symbol *sym;
 	struct elf *elf;
 
@@ -1203,29 +1202,13 @@ struct elf *elf_create_file(GElf_Ehdr *ehdr, const char *name)
 
 	INIT_LIST_HEAD(&elf->sections);
 
-	dir = strdup(name);
-	if (!dir) {
-		ERROR_GLIBC("strdup");
-		return NULL;
-	}
-
-	dir = dirname(dir);
-
-	base = strdup(name);
-	if (!base) {
-		ERROR_GLIBC("strdup");
-		return NULL;
-	}
-
-	base = basename(base);
-
-	tmp_name = malloc(256);
+	tmp_name = malloc(strlen(name) + 8);
 	if (!tmp_name) {
 		ERROR_GLIBC("malloc");
 		return NULL;
 	}
 
-	snprintf(tmp_name, 256, "%s/%s.XXXXXX", dir, base);
+	sprintf(tmp_name, "%s.XXXXXX", name);
 
 	elf->fd = mkstemp(tmp_name);
 	if (elf->fd == -1) {