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authorDenis Vlasenko2007-03-15 00:57:01 +0000
committerDenis Vlasenko2007-03-15 00:57:01 +0000
commit972288e62fa0798f59caf209ab58c911d289a8b2 (patch)
tree4d11a46c5e62a35d357fce9659577cecec8ea117
parentdd2b2f75ae3a826731ae40a79812ebe94c58ac88 (diff)
downloadbusybox-972288e62fa0798f59caf209ab58c911d289a8b2.zip
busybox-972288e62fa0798f59caf209ab58c911d289a8b2.tar.gz
modify ptr_to_globals trick so that we do not violate
type safety (well, sort of ;))
-rw-r--r--archival/gzip.c9
-rw-r--r--docs/keep_data_small.txt17
-rw-r--r--include/libbb.h4
-rw-r--r--libbb/messages.c3
4 files changed, 20 insertions, 13 deletions
diff --git a/archival/gzip.c b/archival/gzip.c
index 9411e17..68f1cc8 100644
--- a/archival/gzip.c
+++ b/archival/gzip.c
@@ -235,7 +235,7 @@ enum {
};
-struct global1 {
+struct globals {
lng block_start;
@@ -343,7 +343,6 @@ struct global1 {
uint32_t crc; /* shift register contents */
};
-extern struct global1 *ptr_to_globals;
#define G1 (*(ptr_to_globals - 1))
@@ -869,7 +868,7 @@ typedef struct tree_desc {
int max_code; /* largest code with non zero frequency */
} tree_desc;
-struct global2 {
+struct globals2 {
ush heap[HEAP_SIZE]; /* heap used to build the Huffman trees */
int heap_len; /* number of elements in the heap */
@@ -956,7 +955,7 @@ struct global2 {
ulg compressed_len; /* total bit length of compressed file */
};
-#define G2ptr ((struct global2*)(ptr_to_globals))
+#define G2ptr ((struct globals2*)(ptr_to_globals))
#define G2 (*G2ptr)
@@ -2048,7 +2047,7 @@ int gzip_main(int argc, char **argv)
}
#endif
- ptr_to_globals = xzalloc(sizeof(struct global1) + sizeof(struct global2));
+ ptr_to_globals = xzalloc(sizeof(struct globals) + sizeof(struct globals2));
ptr_to_globals++;
G2.l_desc.dyn_tree = G2.dyn_ltree;
G2.l_desc.static_tree = G2.static_ltree;
diff --git a/docs/keep_data_small.txt b/docs/keep_data_small.txt
index 272aa21..ec13b4d 100644
--- a/docs/keep_data_small.txt
+++ b/docs/keep_data_small.txt
@@ -59,30 +59,33 @@ archival/libunarchive/decompress_unzip.c:
This example completely eliminates globals in that module.
Required memory is allocated in inflate_gunzip() [its main module]
-and then passed down to all subroutines which need to access globals
+and then passed down to all subroutines which need to access 'globals'
as a parameter.
Example 2
In case you don't want to pass this additional parameter everywhere,
take a look at archival/gzip.c. Here all global data is replaced by
-singe global pointer (ptr_to_globals) to allocated storage.
+single global pointer (ptr_to_globals) to allocated storage.
In order to not duplicate ptr_to_globals in every applet, you can
reuse single common one. It is defined in libbb/messages.c
-as void *ptr_to_globals, but is NOT declared in libbb.h.
-You first define a struct:
+as struct globals *ptr_to_globals, but the struct globals is
+NOT defined in libbb.h. You first define your own struct:
-struct my_globals { int a; char buf[1000]; };
+struct globals { int a; char buf[1000]; };
and then declare that ptr_to_globals is a pointer to it:
-extern struct my_globals *ptr_to_globals;
#define G (*ptr_to_globals)
-Linker magic enures that these two merge into single pointer object.
+Linker magic ensures that these two merge into single pointer object.
Now initialize it in <applet>_main():
ptr_to_globals = xzalloc(sizeof(G));
and you can reference "globals" by G.a, G.buf and so on, in any function.
+
+The drawback is that now you have to initialize it by hand. xzalloc()
+can be helpful in clearing allocated storage to 0, but anything more
+must be done by hand.
diff --git a/include/libbb.h b/include/libbb.h
index 9ea9f5a..9a6966d 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -806,6 +806,10 @@ extern const int const_int_1;
#define BUFSIZ 4096
#endif
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;
/* 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 39bb4c9..1a10a8c 100644
--- a/libbb/messages.c
+++ b/libbb/messages.c
@@ -56,4 +56,5 @@ WTMP_FILE;
char bb_common_bufsiz1[BUFSIZ+1];
-void *ptr_to_globals;
+struct globals;
+struct globals *ptr_to_globals;