On 05/23/2013 10:10 PM, Geert Uytterhoeven wrote: > On Thu, May 23, 2013 at 2:50 PM, Russell King - ARM Linux > <li...@arm.linux.org.uk> wrote: >> > On Thu, May 23, 2013 at 02:09:02PM +0200, Arnd Bergmann wrote: >>> >> On Thursday 23 May 2013, Russell King - ARM Linux wrote: >>>> >> > This is the problem you guys are missing - unreachable() means "we >>>> >> > lose >>>> >> > control of the CPU at this point". >>> >> >>> >> I'm absolutely aware of this. Again, the current behaviour of doing >>> >> nothing >>> >> at all isn't very different from undefined behavior when you get when you >>> >> get to the end of a function returning a pointer without a "return" >>> >> statement, >>> >> or when you return from a function that has determined that it is not >>> >> safe >>> >> to continue. >> > >> > Running off the end of a function like that is a different kettle of fish. >> > The execution path is still as the compiler intends - what isn't is that >> > the data returned is likely to be random trash. >> > >> > That's _quite_ different from the CPU starting to execute the contents >> > of a literal data pool. > I agree it's best to e.g. trap and reboot.
After read the arch/*/include/asm/bug.h, It seems panic() is not suitable for NOMMU platforms (only m68k use it, also need CONFIG_BUG and CONFIG_SUN3 enabled). And unreachable() is need followed with an asm inline instruction (arm, x86, powerpc mips...). And __builtin_trap() is "the mechanism used may vary from release to release so should not rely on any particular implementation" (ref to "http://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html";, used by m68k, sparc, ia64). I can not find any *trap*() and *unreachable*() in "include/asm-generic/" I can not find any suitable implementation which 'generic' enough to add in "include/asm-generic/" (and in fact, CONFIG_BUG itself is not 'generic' enough to be in "include/asm-generic/"). At last, I still suggest to delete CONFIG_BUG, so most of architectures can skip this issue firstly. Then for specific architectures, also can get 3 benefits: a. the related maintainers can implement it as their own willing (not need discus it with another platform maintainers again); b. the related maintainers can free use the platform specific features (which can not be used in "include/asm-generic/"); c. the related maintainers are more familiar their own architectures demands and requirements. ----------- arch/m68k/include/asm/bug.h -------------------------------- 1 #ifndef _M68K_BUG_H 2 #define _M68K_BUG_H 3 4 #ifdef CONFIG_MMU 5 #ifdef CONFIG_BUG 6 #ifdef CONFIG_DEBUG_BUGVERBOSE 7 #ifndef CONFIG_SUN3 8 #define BUG() do { \ 9 printk("kernel BUG at %s:%d!\n", __FILE__, __LINE__); \ 10 __builtin_trap(); \ 11 } while (0) 12 #else 13 #define BUG() do { \ 14 printk("kernel BUG at %s:%d!\n", __FILE__, __LINE__); \ 15 panic("BUG!"); \ 16 } while (0) 17 #endif 18 #else 19 #define BUG() do { \ 20 __builtin_trap(); \ 21 } while (0) 22 #endif 23 24 #define HAVE_ARCH_BUG 25 #endif 26 #endif /* CONFIG_MMU */ 27 28 #include <asm-generic/bug.h> 29 30 #endif Thanks. -- Chen Gang Asianux Corporation _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
