Messages in this thread | | | Date | Wed, 26 Apr 2017 14:24:25 -0700 | Subject | Re: [PATCH v2] x86/mm/kaslr: Use _ASM_MUL macro for multiplication | From | hpa@zytor ... |
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On April 26, 2017 2:21:25 PM PDT, Kees Cook <keescook@chromium.org> wrote: >On Wed, Apr 26, 2017 at 2:00 PM, <hpa@zytor.com> wrote: >> On April 26, 2017 1:55:04 PM PDT, Matthias Kaehlcke ><mka@chromium.org> wrote: >>>In difference to gas clang doesn't seem to infer the size from the >>>operands. Add and use the _ASM_MUL macro which determines the operand >>>size and resolves to the 'mul' instruction with the corresponding >>>suffix. >>> >>>This fixes the following error when building with clang: >>> >>>CC arch/x86/lib/kaslr.o >>>/tmp/kaslr-dfe1ad.s: Assembler messages: >>>/tmp/kaslr-dfe1ad.s:182: Error: no instruction mnemonic suffix given >>>and >>>no register operands; can't size instruction >>> >>>Signed-off-by: Matthias Kaehlcke <mka@chromium.org> >>>--- >>>Changes in v2: >>>- use _ASM_MUL instead of #ifdef >>>- updated commit message >>> >>> arch/x86/include/asm/asm.h | 1 + >>> arch/x86/lib/kaslr.c | 3 ++- >>> 2 files changed, 3 insertions(+), 1 deletion(-) >>> >>>diff --git a/arch/x86/include/asm/asm.h b/arch/x86/include/asm/asm.h >>>index 7acb51c49fec..7a9df3beb89b 100644 >>>--- a/arch/x86/include/asm/asm.h >>>+++ b/arch/x86/include/asm/asm.h >>>@@ -32,6 +32,7 @@ >>> #define _ASM_ADD __ASM_SIZE(add) >>> #define _ASM_SUB __ASM_SIZE(sub) >>> #define _ASM_XADD __ASM_SIZE(xadd) >>>+#define _ASM_MUL __ASM_SIZE(mul) >>> >>> #define _ASM_AX __ASM_REG(ax) >>> #define _ASM_BX __ASM_REG(bx) >>>diff --git a/arch/x86/lib/kaslr.c b/arch/x86/lib/kaslr.c >>>index 121f59c6ee54..0c7fe444dcdd 100644 >>>--- a/arch/x86/lib/kaslr.c >>>+++ b/arch/x86/lib/kaslr.c >>>@@ -5,6 +5,7 @@ >>> * kernel starts. This file is included in the compressed kernel and >>> * normally linked in the regular. >>> */ >>>+#include <asm/asm.h> >>> #include <asm/kaslr.h> >>> #include <asm/msr.h> >>> #include <asm/archrandom.h> >>>@@ -79,7 +80,7 @@ unsigned long kaslr_get_random_long(const char >>>*purpose) >>> } >>> >>> /* Circular multiply for better bit diffusion */ >>>- asm("mul %3" >>>+ asm(_ASM_MUL "%3" >>> : "=a" (random), "=d" (raw) >>> : "a" (random), "rm" (mix_const)); >>> random += raw; >> >> This really feels like a "fix your compiler" issue. > >We already use the other forms, what's so bad about adding mul too? >And if this lets us build under clang, all the better. > >-Kees
It's not bad per se, but if this doesn't eventually gets fixed in clang we'll have no end of this crap. -- Sent from my Android device with K-9 Mail. Please excuse my brevity.
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