Messages in this thread | | | From | Kees Cook <> | Date | Wed, 26 Apr 2017 14:21:25 -0700 | Subject | Re: [PATCH v2] x86/mm/kaslr: Use _ASM_MUL macro for multiplication |
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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
-- Kees Cook Pixel Security
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