From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeroen Hofstee Date: Thu, 11 Sep 2014 22:12:32 +0200 Subject: [U-Boot] [PATCH v3 0/8] add clang support for some ARM boards In-Reply-To: References: <1406750096-7281-1-git-send-email-jeroen@myspectrum.nl> <1410372532-8106-1-git-send-email-jeroen@myspectrum.nl> <1410434240.21166.21.camel@yellow> Message-ID: <54120230.2090702@myspectrum.nl> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: u-boot@lists.denx.de Hello Albert, On 11-09-14 15:31, Albert ARIBAUD wrote: >> Thanks, tested building rpi_b, it works now. >> >> The, tested on versatileqemu out of curiosity and got the following >> results: >> >> 1. >> >> clang warns about Unused static functions in common/console.c, namely >> console_printdevs and console_doenv (1). Why gcc does not flag this? >> We have -Wall set which is supposed to imply -Wunused-functions. >> It is a gcc feature, see [1]: "Warn whenever a static function is >> declared but not defined or a _non-inline static function_ is unused. >> This warning is enabled by -Wall." > Ok, I'll assume there is some logic in there, but then, clang does not > follow that logic -- so which one is the 'good' one? Or maybe that's > the same as the second issue, where... well I don't know the details, but the compiler should not emit a warning if the static inline came from a header file, perhaps that is motivation behind it. Anyway I have a branch with 60 patches or so fixing warnings, don't bother too much about them for the time being. >>> 2. >>> >>> clang errors on arch/arm/lib/cache.c:28 for this: >>> asm("0: mrc p15, 0, r15, c7, c10, 3\n\t" "bne 0b\n" : : : "memory"); >>> and that is a clang mistake, as for ARM926EJS r15 is a valid (albeit >>> quite special semantically) Rd for Test and Clean DCache, see page 2-24. >>> >> This is the integrated-as complaining (the README tells you to disable >> it for the moment). The clang folks push UAL hard, up to a point we need >> to think about minimum gcc version etc. To avoid that, I just left out >> such changes and just use gas instead, at least for the time being. >> Below are some changes to compile versatileqemu with llvm integrated-as >> and gcc/gas. No idea if it actually boots though. >> [..] >> ~ "mrc p15, 0, r15, c7, c14, 3\n" >> + "mrc p15, 0, apsr_nzcv, c7, c14, 3\n" > Is this is a hack to set the Rd field of the mrc instruction to a value > equal to what "r15" would have given, but fooling clang by using an > unrelated and, in this context, meaningless, symbol instead of "r15"? > Nope, it is UAL syntax, binutils agrees: > arm-linux-gnueabi-objdump -S u-boot flush_dcache: mrc p15, 0, r15, c7, c10, 3 10320: ee17ff7a mrc 15, 0, APSR_nzcv, cr7, cr10, {3} Clang is just pushing it a bit harder. I have a branch for that too, but as said, I will let it bit-rot for a while, since that would require about minimal gcc versions and other boring stuff. Regards, Jeroen