gzip: Improve ptr_to_globals trick, allowing gcc

to optimize better. -480 bytes.

3 files changed, 8 insertions, 4 deletions

diff --git a/archival/gzip.c b/archival/gzip.c
index 6af6c1886..c2333e3b1 100644
--- a/archival/gzip.c
+++ b/archival/gzip.c
@@ -2045,8 +2045,8 @@ int gzip_main(int argc, char **argv)
         }
 #endif
 
-        ptr_to_globals = xzalloc(sizeof(struct globals) + sizeof(struct globals2));
-        ptr_to_globals++;
+        PTR_TO_GLOBALS = xzalloc(sizeof(struct globals) + sizeof(struct globals2))
+                        + sizeof(struct globals);
         G2.l_desc.dyn_tree    = G2.dyn_ltree;
         G2.l_desc.static_tree = G2.static_ltree;
         G2.l_desc.extra_bits  = extra_lbits;
diff --git a/include/libbb.h b/include/libbb.h
index 90fb0ad91..d68519dfa 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -804,7 +804,10 @@ extern char bb_common_bufsiz1[BUFSIZ+1];
 /* This struct is deliberately not defined. */
 /* See docs/keep_data_small.txt */
 struct globals;
-extern struct globals *ptr_to_globals;
+/* Magic prevents this from going into rodata */
+/* If you want to assign a value, use PTR_TO_GLOBALS = xxx */
+extern struct globals *const ptr_to_globals;
+#define PTR_TO_GLOBALS (*(struct globals**)&ptr_to_globals)
 
 /* You can change LIBBB_DEFAULT_LOGIN_SHELL, but don't use it,
  * use bb_default_login_shell and following defines.
diff --git a/libbb/messages.c b/libbb/messages.c
index 1a10a8c9e..12a165ad7 100644
--- a/libbb/messages.c
+++ b/libbb/messages.c
@@ -57,4 +57,5 @@ WTMP_FILE;
 char bb_common_bufsiz1[BUFSIZ+1];
 
 struct globals;
-struct globals *ptr_to_globals;
+/* Make it reside in R/W memory: */
+struct globals *const ptr_to_globals __attribute__ ((section (".data")));