GCC warning is clang error, implicitly defined functions and different signature in the source file.

[Quuxplusone]

Bugzilla Link	PR3592
Status	RESOLVED FIXED
Importance	P normal
Reported by	bolzoni (bolzoni@cs.unipr.it)
Reported on	2009-02-16 03:27:34 -0800
Last modified on	2010-03-12 00:57:46 -0800
Version	unspecified
Hardware	All All
CC	bagnara@cs.unipr.it, dgregor@apple.com, llvm-bugs@lists.llvm.org
Fixed by commit(s)
Attachments
Blocks
Blocked by
See also

Here a test case:
------>
static void* malloc(int);
static void* malloc(int size) {
  return ((void*)0); /*do not use heap in this file*/
}
------<
until I do not include stdlib.h we have:
$ gcc -c mall.c
mall.c:2: warning: conflicting types for built-in function ‘malloc’
$ clang mall.c
mall.c:2:14: error: conflicting types for 'malloc'
static void* malloc(int);
             ^
mall.c:2:14: note: 'malloc' was implicitly declared here with type 'void
*(unsigned long)'
2 diagnostics generated.
$

While clang has this behaviour since long time, it seems sometime after r64376
the signature of malloc changed to void*(*)(unsigned long) and the linux-2.4.37
kernel can not compile any more for this error.

[Quuxplusone]

This has been fixed in r64639. We now:

  - Warn when a builtin is redeclared with an incompatible signature
  - Error when a builtin is defined (if used as a hosted implementation)
  - Suppress the generation of builtins when the option -ffreestanding is provided

I assume that the Linux kernel is building with -ffreestanding?

[Quuxplusone]

The linux kernel 2.4.37 does not need using `-ffreestanding' gcc flag.
So it is still impossible compile it with clang.

[Quuxplusone]

Ah, I see. Statics won't collide with standard library functions, since they aren't visible outside of that translation unit. This probably is fixed in r64736, for real.

[Quuxplusone]

Compilation of linux-2.4.37 still fails in linux-2.4.37/lib.  There, string.c
is compiled with

-D__KERNEL__ -I/home/roberto/eclair/eclair/tests/linux/linux-2.4.37/include \
-Wall -Wstrict-prototypes -Wno-trigraphs -O2 -fno-strict-aliasing -fno-common \
-fno-builtin-strpbrk -fno-builtin-sprintf -fomit-frame-pointer  -mno-red-zone \
-mcmodel=kernel -pipe -fno-reorder-blocks -finline-limit=2000 \
-fno-strength-reduce -Wno-sign-compare -fno-asynchronous-unwind-tables \
-fno-unit-at-a-time -march=nocona   -nostdinc -iwithprefix include \
-DKBUILD_BASENAME=string  -c -o string.o string.c

which results into the following errors:

string.c:63:8: error: definition of library function 'strcpy' in a hosted implem
entation
char * strcpy(char * dest,const char *src)
       ^
string.c:63:8: note: use -ffreestanding to compile as a freestanding implementat
ion
string.c:84:8: error: definition of library function 'strncpy' in a hosted imple
mentation
char * strncpy(char * dest,const char *src,size_t count)
       ^
string.c:84:8: note: use -ffreestanding to compile as a freestanding implementat
ion
string.c:101:8: error: definition of library function 'strcat' in a hosted imple
mentation
char * strcat(char * dest, const char * src)
       ^
string.c:101:8: note: use -ffreestanding to compile as a freestanding implementa
tion
string.c:124:8: error: definition of library function 'strncat' in a hosted impl
ementation
char * strncat(char *dest, const char *src, size_t count)
       ^
string.c:124:8: note: use -ffreestanding to compile as a freestanding implementa
tion
string.c:189:8: error: definition of library function 'strchr' in a hosted imple
mentation
char * strchr(const char * s, int c)
       ^
string.c:189:8: note: use -ffreestanding to compile as a freestanding implementa
tion
string.c:204:8: error: definition of library function 'strrchr' in a hosted impl
ementation
char * strrchr(const char * s, int c)
       ^
string.c:204:8: note: use -ffreestanding to compile as a freestanding implementa
tion
string.c:220:8: error: definition of library function 'strlen' in a hosted imple
mentation
size_t strlen(const char * s)
       ^
string.c:220:8: note: use -ffreestanding to compile as a freestanding implementa
tion
string.c:253:8: error: definition of library function 'strspn' in a hosted imple
mentation
size_t strspn(const char *s, const char *accept)
       ^
string.c:253:8: note: use -ffreestanding to compile as a freestanding implementa
tion
string.c:279:8: error: definition of library function 'strpbrk' in a hosted impl
ementation
char * strpbrk(const char * cs,const char * ct)
       ^
string.c:279:8: note: use -ffreestanding to compile as a freestanding implementa
tion
string.c:493:8: error: definition of library function 'strstr' in a hosted imple
mentation
char * strstr(const char * s1,const char * s2)
       ^
string.c:493:8: note: use -ffreestanding to compile as a freestanding implementa
tion

The compilation of vsprintf.c in the same directory fails in the same way:

vsprintf.c:234:5: error: definition of library function 'vsnprintf' in a hosted
implementation
int vsnprintf(char *buf, size_t size, const char *fmt, va_list args)
    ^
vsprintf.c:234:5: note: use -ffreestanding to compile as a freestanding implemen
tation
vsprintf.c:481:5: error: definition of library function 'snprintf' in a hosted i
mplementation
int snprintf(char * buf, size_t size, const char *fmt, ...)
    ^
vsprintf.c:481:5: note: use -ffreestanding to compile as a freestanding implemen
tation
vsprintf.c:501:5: error: definition of library function 'vsprintf' in a hosted i
mplementation
int vsprintf(char *buf, const char *fmt, va_list args)
    ^
vsprintf.c:501:5: note: use -ffreestanding to compile as a freestanding implemen
tation
vsprintf.c:513:5: error: definition of library function 'sprintf' in a hosted im
plementation
int sprintf(char * buf, const char *fmt, ...)
    ^
vsprintf.c:513:5: note: use -ffreestanding to compile as a freestanding implemen
tation

In linux-2.4.37/arch/x86_64/lib, the compilation of memmove.c fails:

memmove.c:8:7: error: definition of library function 'memmove' in a hosted imple
mentation
void *memmove(void * dest,const void *src,size_t count)
      ^
memmove.c:8:7: note: use -ffreestanding to compile as a freestanding implementat
ion

[Quuxplusone]

I've removed the offending diagnostic in r64767.