Building kernels before linux-4.7 with gcc-8 results in many build failures when gcc triggers a check that was meant to catch broken compilers:
/tmp/ccCGMQmS.s:648: Error: .err encountered
According to the discussion in the gcc bugzilla, a local "register asm()" variable is still supposed to be the correct way to force an inline assembly to use a particular register, but marking it 'const' lets the compiler do optimizations that break that, i.e the compiler is free to treat the variable as either 'const' or 'register' in that case.
Upstream commit 9f73bd8bb445 ("ARM: uaccess: remove put_user() code duplication") fixed this problem in linux-4.8 as part of a larger change, but seems a little too big to be backported to 4.4.
Let's take the simplest fix and change only the one broken line in the same way as newer kernels.
Suggested-by: Bernd Edlinger bernd.edlinger@hotmail.de Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85745 Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86673 Signed-off-by: Arnd Bergmann arnd@arndb.de --- This should also apply to older kernels before 4.4, but I did not try that. Presumably they have additional problems with modern compilers anyway.
arch/arm/include/asm/uaccess.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/arm/include/asm/uaccess.h b/arch/arm/include/asm/uaccess.h index 35c9db857ebe..cd8b589111ba 100644 --- a/arch/arm/include/asm/uaccess.h +++ b/arch/arm/include/asm/uaccess.h @@ -251,7 +251,7 @@ extern int __put_user_8(void *, unsigned long long); ({ \ unsigned long __limit = current_thread_info()->addr_limit - 1; \ const typeof(*(p)) __user *__tmp_p = (p); \ - register const typeof(*(p)) __r2 asm("r2") = (x); \ + register typeof(*(p)) __r2 asm("r2") = (x); \ register const typeof(*(p)) __user *__p asm("r0") = __tmp_p; \ register unsigned long __l asm("r1") = __limit; \ register int __e asm("r0"); \