re-add -ffreestanding

I got the following compile error with gcc 4.1.1 when trying to compile kernel 2.6.18-rc4-mm2 for m68k:

<-- snip -->

...
LD .tmp_vmlinux1
arch/m68k/amiga/built-in.o: In function `amiga_get_hardware_list':
config.c:(.text+0x882): undefined reference to strcpy' kernel/built-in.o: In function prof_cpu_mask_read_proc':
profile.c:(.text+0x41ac): undefined reference to strcpy' kernel/built-in.o: In function sysfs_show_available_clocksources':
clocksource.c:(.text+0x1434e): undefined reference to strcpy' kernel/built-in.o: In function sysfs_show_current_clocksources':
clocksource.c:(.text+0x143a4): undefined reference to strcpy' fs/built-in.o: In function lock_get_status':
locks.c:(.text+0x1198a): undefined reference to strcpy' fs/built-in.o:locks.c:(.text+0x119ae): more undefined references to strcpy' follow make[1]: *** [.tmp_vmlinux1] Error 1

<-- snip -->

The Linux kernel is a freestanding environment, not a hosted one providing a full standard C library gcc can consider being present.

The fact that -ffreestanding had already been re-added on three architectures also reflects this fact.

If we want to use a all or subset of the gcc builtins on some or all architectures, we should make this explicitely through #define's.

This patch therefore reverts commit 6edfba1b33c701108717f4e036320fc39abe1912 and re-adds -ffreestanding to the CFLAGS.

---

 Makefile                    |    3 ++-
 arch/i386/Makefile          |    3 ---
 arch/mips/Makefile          |    2 --
 arch/um/Makefile-i386       |    4 ----
 include/asm-x86_64/string.h |   17 ++++++++++++++---
 5 files changed, 16 insertions(+), 13 deletions(-)

@@ -308,7 +308,8 @@
 CPPFLAGS        := -D__KERNEL__ $(LINUXINCLUDE)
 
 CFLAGS          := -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \
-                   -fno-strict-aliasing -fno-common
+		   -fno-strict-aliasing -fno-common \
+		   -ffreestanding
 # Force gcc to behave correct even for buggy distributions
 CFLAGS          += $(call cc-option, -fno-stack-protector)
 

@@ -39,9 +39,6 @@
 
 cflags-$(CONFIG_REGPARM) += -mregparm=3
 
-# temporary until string.h is fixed
-cflags-y += -ffreestanding
-
 # Disable unit-at-a-time mode on pre-gcc-4.0 compilers, it makes gcc use
 # a lot more stack due to the lack of sharing of stacklots:
 CFLAGS				+= $(shell if [ $(call cc-version) -lt 0400 ] ; then echo $(call cc-option,-fno-unit-at-a-time); fi ;)

@@ -83,8 +83,6 @@
 LDFLAGS_vmlinux			+= -G 0 -static -n -nostdlib
 MODFLAGS			+= -mlong-calls
 
-cflags-y += -ffreestanding
-
 #
 # We explicitly add the endianness specifier if needed, this allows
 # to compile kernels with a toolchain for the other endianness. We

@@ -33,9 +33,5 @@
 # prevent gcc from keeping the stack 16 byte aligned. Taken from i386.
 cflags-y += $(call cc-option,-mpreferred-stack-boundary=2)
 
-# Prevent sprintf in nfsd from being converted to strcpy and resulting in
-# an unresolved reference.
-cflags-y += -ffreestanding
-
 CFLAGS += $(cflags-y)
 USER_CFLAGS += $(cflags-y)

@@ -41,15 +41,26 @@
 
 
 #define __HAVE_ARCH_MEMSET
-void *memset(void *s, int c, size_t n);
+#define memset __builtin_memset
 
 #define __HAVE_ARCH_MEMMOVE
 void * memmove(void * dest,const void *src,size_t count);
 
+/* Use C out of line version for memcmp */ 
+#define memcmp __builtin_memcmp
 int memcmp(const void * cs,const void * ct,size_t count);
+
+/* out of line string functions use always C versions */ 
+#define strlen __builtin_strlen
 size_t strlen(const char * s);
-char *strcpy(char * dest,const char *src);
-char *strcat(char * dest, const char * src);
+
+#define strcpy __builtin_strcpy
+char * strcpy(char * dest,const char *src);
+
+#define strcat __builtin_strcat
+char * strcat(char * dest, const char * src);
+
+#define strcmp __builtin_strcmp
 int strcmp(const char * cs,const char * ct);
 
 #endif /* __KERNEL__ */

I object to this change. -ffreestanding shouldn't be forced on everybody

-Andi

Why?

The Linux kernel is a freestanding environment.

Omitting -ffreestanding only for allowing gcc to automatically use builtins isn't a good idea (as we have already seen).

We can easily enable as many gcc builtins as we want. We could even do this for all platforms in include/linux/string.h

It might make sense to do this properly since it could e.g. be the gcc builtins produce no worse code than the inlines in include/asm-i386/string.h.

But if this should be done, let's do it right and explicitely.

cu
Adrian

    Gentoo kernels are 42 times more popular than SUSE kernels among
    KLive users  (a service by SUSE contractor Andrea Arcangeli that
    gathers data about kernels from many users worldwide).

       There are three kinds of lies: Lies, Damn Lies, and Statistics.
                                                    Benjamin Disraeli

Because -ffreestanding does the the wrong thing(tm) for the x86-64 string implementation (which I plan to extend at some point to i386 too BTW). Don't argue with it -- what counts is not the name, but the semantics.

-Andi

It disables the automatic usage of builtins which is OK.

Which other semantics does it have that is causing problems?

cu
Adrian

    Gentoo kernels are 42 times more popular than SUSE kernels among
    KLive users  (a service by SUSE contractor Andrea Arcangeli that
    gathers data about kernels from many users worldwide).

       There are three kinds of lies: Lies, Damn Lies, and Statistics.
                                                    Benjamin Disraeli

No, it's not ok -- it is the problem. We want to use the builtins.

-Andi

Without -ffreestanding, the compiler is completely free to decide whether to use a builtin or whether to not use it - and which other C library functions to use.

Your commit 6edfba1b33c701108717f4e036320fc39abe1912 that claimed "it was only added for x86-64, so dropping it should be safe" was not safe, it had broken at least mips and m68k. This wrong justification alone should warrant a revert of this commit.

What's the problem with adding -ffreestanding and stating explicitely which functions we want to be handled be builtins, and which functions we don't want to be handled by builtins?

This looks like the right way to go instead of breaking other architectures here and there.

cu
Adrian

    Gentoo kernels are 42 times more popular than SUSE kernels among
    KLive users  (a service by SUSE contractor Andrea Arcangeli that
    gathers data about kernels from many users worldwide).

       There are three kinds of lies: Lies, Damn Lies, and Statistics.
                                                    Benjamin Disraeli

Take a look at lib/string.c and think about it a bit.

-Andi

So why can't lib/string.c explicitly say __builtin_foo() instead of foo() where we mean the former? Here's a brief summary:

With -ffreestanding:
__builtin_foo(): Use the GCC built-in if possible, otherwise out-
of-line
foo(): Always use the out-of-line function

Without -ffreestanding:
__builtin_foo(): Use the GCC built-in if possible, otherwise out-
of-line
foo(): Use the GCC built-in if possible, otherwise out-
of-line

What's wrong with always specifying -ffreestanding and using __builtin_foo() instead of foo() where applicable? That's what it was designed for, according to the GCC manual:

http://gcc.gnu.org/onlinedocs/gcc-4.1.1/gcc/C-Dialect-Options.html#C-Dialect-Options

If you want to unconditionally force a certain function to use the GCC built-in on a particular architecture, you could always just do this to get exactly the same result as without -ffreestanding:

#define memcpy(dest, src, len) __builtin_strcpy((dest), (src), (len)) #define memcmp(a, b, len) __builtin_strcmp((a), (b), (len)) [...]

Just stuff those types of defines in an x86-64 specific header somewhere and turn on -ffreestanding unconditionally; you'll fix all of the problems with MIPS, etc, without even changing the semantics on x86-64.

Cheers,
Kyle Moffett

Because gcc when using builtins sometimes decides to call the out of line version (usually when it can't figure out the alignment and generic alignment code would be too large to inline). And it will always call str/memfoo not __builtin_str/memfoo

-Andi

IOW, we might in some cases require an out-of-line version of the function?

I don't see in this case any problem created by using -ffreestanding and the #define's.

cu
Adrian

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

Hi,

I agree and for m68k I have a patch to fix this properly.

bye, Roman