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Re: [Xen-devel] [PATCH] x86emul: correct stub invocation constraints

To: "Boris Ostrovsky" <boris.ostrovsky@xxxxxxxxxx>

From: "Jan Beulich" <JBeulich@xxxxxxxx>

Date: Wed, 26 Apr 2017 08:19:19 -0600

Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Julien Grall <julien.grall@xxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>

Delivery-date: Wed, 26 Apr 2017 14:19:30 +0000

List-id: Xen developer discussion <xen-devel.lists.xen.org>

>>> On 26.04.17 at 16:01, <boris.ostrovsky@xxxxxxxxxx> wrote: > On 04/25/2017 05:04 AM, Jan Beulich wrote: >> Stub invocations need to have the space the stub occupies as an input, >> to prevent the compiler from re-ordering (or omitting) writes to it. >> >> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx> >> >> --- a/xen/arch/x86/x86_emulate/x86_emulate.c >> +++ b/xen/arch/x86/x86_emulate/x86_emulate.c >> @@ -837,7 +837,8 @@ do{ asm volatile ( >> ".popsection\n\t" \ >> _ASM_EXTABLE(.Lret%=, .Lfix%=) \ >> : [exn] "+g" (res_), constraints, \ >> - [stub] "rm" (stub.func) ); \ >> + [stub] "rm" (stub.func), \ >> + "m" (*(uint8_t(*)[MAX_INST_LEN + 1])stub.ptr) ); \ >> if ( unlikely(~res_.raw) ) \ >> { \ >> gprintk(XENLOG_WARNING, \ >> @@ -853,7 +854,8 @@ do{ asm volatile ( >> #else >> # define invoke_stub(pre, post, constraints...) \ >> asm volatile ( pre "\n\tcall *%[stub]\n\t" post \ >> - : constraints, [stub] "rm" (stub.func) ) >> + : constraints, [stub] "rm" (stub.func), \ >> + "m" (*(uint8_t(*)[MAX_INST_LEN + 1])stub.buf) ) >> #endif >> >> #define emulate_stub(dst, src...) do { \ >> > > > This breaks on old compilers: > > FC-64 > <build@build-mk2:~/xtt-x86_64/bootstrap/xen.git/tools/fuzz/x86_instruction_em > ulator> > gcc --version > gcc (GCC) 4.4.4 20100503 (Red Hat 4.4.4-2) I did try with 4.3.x, fwiw (but I'm afraid I've lost that machine just now, and will hardly set it up again using an old distro). Also I can't immediately see what the compiler dislikes and hence how a fix may look like (short of adding memory clobbers instead). Jan > Copyright (C) 2010 Free Software Foundation, Inc. > This is free software; see the source for copying conditions. There is NO > warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. > > FC-64 > <build@build-mk2:~/xtt-x86_64/bootstrap/xen.git/tools/fuzz/x86_instruction_em > ulator> > pwd > /home/build/xtt-x86_64/bootstrap/xen.git/tools/fuzz/x86_instruction_emulator > FC-64 > <build@build-mk2:~/xtt-x86_64/bootstrap/xen.git/tools/fuzz/x86_instruction_em > ulator> > gcc -m64 -DBUILD_ID -fno-strict-aliasing -std=gnu99 -Wall > -Wstrict-prototypes -Wdeclaration-after-statement > -Wno-unused-but-set-variable -g3 -O0 -fno-omit-frame-pointer > -D__XEN_INTERFACE_VERSION__=__XEN_LATEST_INTERFACE_VERSION__ -MMD -MF > .x86_emulate.o.d -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE > -I/home/build/xtt-x86_64/bootstrap/xen.git/tools/fuzz/x86_instruction_emulat > or/../../../tools/include > -D__XEN_TOOLS__ -I. -c -o x86_emulate.o x86_emulate.c > In file included from x86_emulate.c:157: > x86_emulate/x86_emulate.c: In function ‘x86_emulate’: > x86_emulate/x86_emulate.c:4085: error: memory input 3 is not directly > addressable > In file included from x86_emulate.c:157: > x86_emulate/x86_emulate.c:4161: error: memory input 3 is not directly > addressable > In file included from x86_emulate.c:157: > x86_emulate/x86_emulate.c:4226: error: memory input 5 is not directly > addressable > In file included from x86_emulate.c:157: > x86_emulate/x86_emulate.c:4229: error: memory input 3 is not directly > addressable > In file included from x86_emulate.c:157: > x86_emulate/x86_emulate.c:4279: error: memory input 5 is not directly > addressable > In file included from x86_emulate.c:157: > x86_emulate/x86_emulate.c:4288: error: memory input 3 is not directly > addressable > In file included from x86_emulate.c:157: > x86_emulate/x86_emulate.c:4353: error: memory input 3 is not directly > addressable > In file included from x86_emulate.c:157: > x86_emulate/x86_emulate.c:4402: error: memory input 3 is not directly > addressable > In file included from x86_emulate.c:157: > x86_emulate/x86_emulate.c:4465: error: memory input 3 is not directly > addressable > In file included from x86_emulate.c:157: > x86_emulate/x86_emulate.c:4516: error: memory input 5 is not directly > addressable > In file included from x86_emulate.c:157: > x86_emulate/x86_emulate.c:4522: error: memory input 3 is not directly > addressable > In file included from x86_emulate.c:157: > x86_emulate/x86_emulate.c:5632: error: memory input 5 is not directly > addressable > In file included from x86_emulate.c:157: > x86_emulate/x86_emulate.c:5679: error: memory input 8 is not directly > addressable > In file included from x86_emulate.c:157: > x86_emulate/x86_emulate.c:5863: error: memory input 3 is not directly > addressable > x86_emulate/x86_emulate.c:6069: error: memory input 4 is not directly > addressable > x86_emulate/x86_emulate.c:6213: error: memory input 3 is not directly > addressable > In file included from x86_emulate.c:157: > x86_emulate/x86_emulate.c:7029: error: memory input 3 is not directly > addressable > In file included from x86_emulate.c:157: > x86_emulate/x86_emulate.c:7178: error: memory input 6 is not directly > addressable > In file included from x86_emulate.c:157: > x86_emulate/x86_emulate.c:7328: error: memory input 7 is not directly > addressable > In file included from x86_emulate.c:157: > x86_emulate/x86_emulate.c:7362: error: memory input 6 is not directly > addressable > In file included from x86_emulate.c:157: > x86_emulate/x86_emulate.c:7482: error: memory input 3 is not directly > addressable > In file included from x86_emulate.c:157: > x86_emulate/x86_emulate.c:7603: error: memory input 9 is not directly > addressable > In file included from x86_emulate.c:157: > x86_emulate/x86_emulate.c:7607: error: memory input 9 is not directly > addressable > In file included from x86_emulate.c:157: > x86_emulate/x86_emulate.c:7676: error: memory input 6 is not directly > addressable > In file included from x86_emulate.c:157: > x86_emulate/x86_emulate.c:7715: error: memory input 6 is not directly > addressable > In file included from x86_emulate.c:157: > x86_emulate/x86_emulate.c:7795: error: memory input 4 is not directly > addressable > x86_emulate/x86_emulate.c:7798: error: memory input 3 is not directly > addressable > FC-64 > <build@build-mk2:~/xtt-x86_64/bootstrap/xen.git/tools/fuzz/x86_instruction_em > ulator> > > > > -boris _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel

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