[prev in list] [next in list] [prev in thread] [next in thread]
List: busybox
Subject: [PATCH] use BB_GLOBAL_CONST where applicable
From: Luís Marques <luismarques () lowrisc ! org>
Date: 2019-06-17 12:25:11
Message-ID: 20190617122509.28091-1-luismarques () lowrisc ! org
[Download RAW message or body]
Re-sending patch using git send-mail.
---
coreutils/test.c | 3 +--
coreutils/test_ptr_hack.c | 2 +-
include/libbb.h | 27 +++++++++++++++++++++++++--
libbb/lineedit.c | 3 +--
libbb/lineedit_ptr_hack.c | 2 +-
libbb/ptr_to_globals.c | 2 +-
shell/ash.c | 13 -------------
shell/ash_ptr_hack.c | 6 +++---
8 files changed, 33 insertions(+), 25 deletions(-)
diff --git a/coreutils/test.c b/coreutils/test.c
index 8d7dac025..e1d440106 100644
--- a/coreutils/test.c
+++ b/coreutils/test.c
@@ -400,8 +400,7 @@ struct test_statics {
jmp_buf leaving;
};
-/* See test_ptr_hack.c */
-extern struct test_statics *const test_ptr_to_statics;
+extern struct test_statics *BB_GLOBAL_CONST test_ptr_to_statics;
#define S (*test_ptr_to_statics)
#define args (S.args )
diff --git a/coreutils/test_ptr_hack.c b/coreutils/test_ptr_hack.c
index 5ba9dcc68..6759b2144 100644
--- a/coreutils/test_ptr_hack.c
+++ b/coreutils/test_ptr_hack.c
@@ -18,6 +18,6 @@ struct test_statics *test_ptr_to_statics;
/* gcc -combine will see through and complain */
/* Using alternative method which is more likely to break
* on weird architectures, compilers, linkers and so on */
-struct test_statics *const test_ptr_to_statics __attribute__ ((section (".data")));
+struct test_statics *BB_GLOBAL_CONST test_ptr_to_statics __attribute__ ((section \
(".data")));
#endif
diff --git a/include/libbb.h b/include/libbb.h
index 100d6b606..d0b9eccd9 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -338,10 +338,33 @@ struct BUG_off_t_size_is_misdetected {
#endif
#endif
+/* We use a trick to have more optimized code (fewer pointer reloads). E.g.:
+ * ash.c: extern struct globals *const ash_ptr_to_globals;
+ * ash_ptr_hack.c: struct globals *ash_ptr_to_globals;
+ * This way, compiler in ash.c knows the pointer cannot change.
+ *
+ * However, this relies on C undefined behavior, so we whitelist compilers
+ * where we know this isn't problematic, by using the the BB_GLOBAL_CONST
+ * preprocessor definition.
+ * If you are sure this trick also works with your toolchain you can add
+ * "-DBB_GLOBAL_CONST='const'" to CONFIG_EXTRA_CFLAGS or add your compiler to
+ * the whitelist below.
+ */
+
+#ifndef BB_GLOBAL_CONST
+# if defined(__clang__)
+# define BB_GLOBAL_CONST
+# elif defined(__GNUC__)
+# define BB_GLOBAL_CONST const
+# else
+# define BB_GLOBAL_CONST
+# endif
+#endif
+
#if defined(__GLIBC__)
/* glibc uses __errno_location() to get a ptr to errno */
/* We can just memorize it once - no multithreading in busybox :) */
-extern int *const bb_errno;
+extern int *BB_GLOBAL_CONST bb_errno;
#undef errno
#define errno (*bb_errno)
#endif
@@ -2108,7 +2131,7 @@ struct globals;
/* '*const' ptr makes gcc optimize code much better.
* Magic prevents ptr_to_globals from going into rodata.
* If you want to assign a value, use SET_PTR_TO_GLOBALS(x) */
-extern struct globals *const ptr_to_globals;
+extern struct globals *BB_GLOBAL_CONST ptr_to_globals;
/* At least gcc 3.4.6 on mipsel system needs optimization barrier */
#define barrier() __asm__ __volatile__("":::"memory")
#define SET_PTR_TO_GLOBALS(x) do { \
diff --git a/libbb/lineedit.c b/libbb/lineedit.c
index fbabc6c12..b9e9719c5 100644
--- a/libbb/lineedit.c
+++ b/libbb/lineedit.c
@@ -180,8 +180,7 @@ struct lineedit_statics {
#endif
};
-/* See lineedit_ptr_hack.c */
-extern struct lineedit_statics *const lineedit_ptr_to_statics;
+extern struct lineedit_statics *BB_GLOBAL_CONST lineedit_ptr_to_statics;
#define S (*lineedit_ptr_to_statics)
#define state (S.state )
diff --git a/libbb/lineedit_ptr_hack.c b/libbb/lineedit_ptr_hack.c
index dc45855d5..ac33bd409 100644
--- a/libbb/lineedit_ptr_hack.c
+++ b/libbb/lineedit_ptr_hack.c
@@ -18,6 +18,6 @@ struct lineedit_statics *lineedit_ptr_to_statics;
/* gcc -combine will see through and complain */
/* Using alternative method which is more likely to break
* on weird architectures, compilers, linkers and so on */
-struct lineedit_statics *const lineedit_ptr_to_statics __attribute__ ((section \
(".data"))); +struct lineedit_statics *BB_GLOBAL_CONST lineedit_ptr_to_statics \
__attribute__ ((section (".data")));
#endif
diff --git a/libbb/ptr_to_globals.c b/libbb/ptr_to_globals.c
index 8ba9cd154..26d7b2042 100644
--- a/libbb/ptr_to_globals.c
+++ b/libbb/ptr_to_globals.c
@@ -25,7 +25,7 @@ int *bb_errno;
/* gcc -combine will see through and complain */
/* Using alternative method which is more likely to break
* on weird architectures, compilers, linkers and so on */
-struct globals *const ptr_to_globals __attribute__ ((section (".data")));
+struct globals *BB_GLOBAL_CONST ptr_to_globals __attribute__ ((section (".data")));
#ifdef __GLIBC__
int *const bb_errno __attribute__ ((section (".data")));
diff --git a/shell/ash.c b/shell/ash.c
index e3bbac9a0..3141f3812 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -288,19 +288,6 @@ typedef long arith_t;
# error "Do not even bother, ash will not run on NOMMU machine"
#endif
-/* We use a trick to have more optimized code (fewer pointer reloads):
- * ash.c: extern struct globals *const ash_ptr_to_globals;
- * ash_ptr_hack.c: struct globals *ash_ptr_to_globals;
- * This way, compiler in ash.c knows the pointer can not change.
- *
- * However, this may break on weird arches or toolchains. In this case,
- * set "-DBB_GLOBAL_CONST=''" in CONFIG_EXTRA_CFLAGS to disable
- * this optimization.
- */
-#ifndef BB_GLOBAL_CONST
-# define BB_GLOBAL_CONST const
-#endif
-
/* ============ Hash table sizes. Configurable. */
diff --git a/shell/ash_ptr_hack.c b/shell/ash_ptr_hack.c
index f69840825..af16cca27 100644
--- a/shell/ash_ptr_hack.c
+++ b/shell/ash_ptr_hack.c
@@ -22,8 +22,8 @@ struct globals_var *ash_ptr_to_globals_var;
/* gcc -combine will see through and complain */
/* Using alternative method which is more likely to break
* on weird architectures, compilers, linkers and so on */
-struct globals_misc *const ash_ptr_to_globals_misc __attribute__ ((section \
(".data")));
-struct globals_memstack *const ash_ptr_to_globals_memstack __attribute__ ((section \
(".data")));
-struct globals_var *const ash_ptr_to_globals_var __attribute__ ((section \
(".data"))); +struct globals_misc *BB_GLOBAL_CONST ash_ptr_to_globals_misc \
__attribute__ ((section (".data"))); +struct globals_memstack *BB_GLOBAL_CONST \
ash_ptr_to_globals_memstack __attribute__ ((section (".data"))); +struct globals_var \
*BB_GLOBAL_CONST ash_ptr_to_globals_var __attribute__ ((section (".data")));
#endif
--
2.19.1
_______________________________________________
busybox mailing list
busybox@busybox.net
http://lists.busybox.net/mailman/listinfo/busybox
[prev in list] [next in list] [prev in thread] [next in thread]
Configure |
About |
News |
Add a list |
Sponsored by KoreLogic