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[uml-devel] Re: [PATCH 3/4] UML - Properly invoke x86_64 system calls
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From: linux-os \(D. Johnson\) <lin...@an...> - 2005-11-17 20:37:47
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On Thu, 17 Nov 2005, Jeff Dike wrote:
> This patch makes stub_segv use the stub_syscall macros. This was
> needed anyway, but the bug that prompted this was the discovery that
> gcc was storing stuff in RCX, which is trashed across a system
> call.
But the C-calling convention used by gcc for 32-bit systems
is supposed to allow the called-function to destroy general-
purpose registers but not index registers. In other words,
ECX, EDX are supposed to be available and EAX is used for
return-values. The register size isn't supposed to have
anything to do with it (longword/quadword)!
In 64-bit world, the same is supposed to apply as well.
If RCX is now precious, it's a GCC bug that should be fixed.
Yes?
This is exactly the sort of problem that the new macros fix.
> There is a stub_syscall0 for getpid.
> stub_segv was changed to be a libc file, and that caused some
> include changes.
>
> Signed-off-by: Jeff Dike <jd...@ad...>
>
> Index: linux-2.6.15/arch/um/include/sysdep-i386/stub.h
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> --- linux-2.6.15.orig/arch/um/include/sysdep-i386/stub.h 2005-11-17=
14:59:30.000000000 -0500
> +++ linux-2.6.15/arch/um/include/sysdep-i386/stub.h 2005-11-17=
14:59:55.000000000 -0500
> @@ -16,6 +16,15 @@
> #define STUB_MMAP_NR __NR_mmap2
> #define MMAP_OFFSET(o) ((o) >> PAGE_SHIFT)
>
> +static inline long stub_syscall0(long syscall)
> +{
> + long ret;
> +
> + __asm__ volatile ("int $0x80" : "=3Da" (ret) : "0" (syscall));
> +
> + return ret;
> +}
> +
> static inline long stub_syscall1(long syscall, long arg1)
> {
> long ret;
> Index: linux-2.6.15/arch/um/include/sysdep-x86_64/stub.h
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> --- linux-2.6.15.orig/arch/um/include/sysdep-x86_64/stub.h 2005-11-17=
14:59:30.000000000 -0500
> +++ linux-2.6.15/arch/um/include/sysdep-x86_64/stub.h 2005-11-17=
14:59:55.000000000 -0500
> @@ -6,7 +6,6 @@
> #ifndef __SYSDEP_STUB_H
> #define __SYSDEP_STUB_H
>
> -#include <asm/ptrace.h>
> #include <asm/unistd.h>
> #include <sysdep/ptrace_user.h>
>
> @@ -20,6 +19,17 @@
> #define __syscall_clobber "r11","rcx","memory"
> #define __syscall "syscall"
>
> +static inline long stub_syscall0(long syscall)
> +{
> + long ret;
> +
> + __asm__ volatile (__syscall
> + : "=3Da" (ret)
> + : "0" (syscall) : __syscall_clobber );
> +
> + return ret;
> +}
> +
> static inline long stub_syscall2(long syscall, long arg1, long arg2)
> {
> long ret;
> Index: linux-2.6.15/arch/um/sys-i386/Makefile
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> --- linux-2.6.15.orig/arch/um/sys-i386/Makefile 2005-11-17=
14:59:30.000000000 -0500
> +++ linux-2.6.15/arch/um/sys-i386/Makefile 2005-11-17 14:59:55.000000000=
-0500
> @@ -5,7 +5,7 @@
> obj-$(CONFIG_HIGHMEM) +=3D highmem.o
> obj-$(CONFIG_MODULES) +=3D module.o
>
> -USER_OBJS :=3D bugs.o ptrace_user.o sigcontext.o fault.o
> +USER_OBJS :=3D bugs.o ptrace_user.o sigcontext.o fault.o stub_segv.o
>
> SYMLINKS =3D bitops.c semaphore.c highmem.c module.c
>
> Index: linux-2.6.15/arch/um/sys-i386/stub_segv.c
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> --- linux-2.6.15.orig/arch/um/sys-i386/stub_segv.c 2005-11-17=
14:59:30.000000000 -0500
> +++ linux-2.6.15/arch/um/sys-i386/stub_segv.c 2005-11-17=
14:59:55.000000000 -0500
> @@ -3,9 +3,11 @@
> * Licensed under the GPL
> */
>
> -#include <asm/signal.h>
> +#include <signal.h>
> +#include <sys/select.h> /* The only way I can see to get sigset_t */
> #include <asm/unistd.h>
> #include "uml-config.h"
> +#include "sysdep/stub.h"
> #include "sysdep/sigcontext.h"
> #include "sysdep/faultinfo.h"
>
> @@ -13,13 +15,14 @@
> stub_segv_handler(int sig)
> {
> struct sigcontext *sc =3D (struct sigcontext *) (&sig + 1);
> + int pid;
>
> GET_FAULTINFO_FROM_SC(*((struct faultinfo *) UML_CONFIG_STUB_DATA),
> sc);
>
> - __asm__("movl %0, %%eax ; int $0x80": : "g" (__NR_getpid));
> - __asm__("movl %%eax, %%ebx ; movl %0, %%eax ; movl %1, %%ecx ;"
> - "int $0x80": : "g" (__NR_kill), "g" (SIGUSR1));
> + pid =3D stub_syscall0(__NR_getpid);
> + stub_syscall2(__NR_kill, pid, SIGUSR1);
> +
> /* Load pointer to sigcontext into esp, since we need to leave
> * the stack in its original form when we do the sigreturn here, by
> * hand.
> Index: linux-2.6.15/arch/um/sys-x86_64/Makefile
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> --- linux-2.6.15.orig/arch/um/sys-x86_64/Makefile 2005-11-17=
14:59:30.000000000 -0500
> +++ linux-2.6.15/arch/um/sys-x86_64/Makefile 2005-11-17=
14:59:55.000000000 -0500
> @@ -12,7 +12,7 @@
> obj-y :=3D ksyms.o
> obj-$(CONFIG_MODULES) +=3D module.o um_module.o
>
> -USER_OBJS :=3D ptrace_user.o sigcontext.o
> +USER_OBJS :=3D ptrace_user.o sigcontext.o stub_segv.o
>
> SYMLINKS =3D bitops.c csum-copy.S csum-partial.c csum-wrappers.c ldt.c=
memcpy.S \
> thunk.S module.c
> Index: linux-2.6.15/arch/um/sys-x86_64/stub_segv.c
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> --- linux-2.6.15.orig/arch/um/sys-x86_64/stub_segv.c 2005-11-17=
14:59:30.000000000 -0500
> +++ linux-2.6.15/arch/um/sys-x86_64/stub_segv.c 2005-11-17=
15:12:23.000000000 -0500
> @@ -3,14 +3,14 @@
> * Licensed under the GPL
> */
>
> -#include <asm/signal.h>
> +#include <stddef.h>
> +#include <signal.h>
> #include <linux/compiler.h>
> #include <asm/unistd.h>
> -#include <asm/ucontext.h>
> #include "uml-config.h"
> #include "sysdep/sigcontext.h"
> #include "sysdep/faultinfo.h"
> -#include <stddef.h>
> +#include "sysdep/stub.h"
>
> /* Copied from sys-x86_64/signal.c - Can't find an equivalent definition
> * in the libc headers anywhere.
> @@ -31,21 +31,21 @@
> stub_segv_handler(int sig)
> {
> struct ucontext *uc;
> + int pid;
>
> __asm__("movq %%rdx, %0" : "=3Dg" (uc) :);
> GET_FAULTINFO_FROM_SC(*((struct faultinfo *) UML_CONFIG_STUB_DATA),
> &uc->uc_mcontext);
>
> - __asm__("movq %0, %%rax ; syscall": : "g" (__NR_getpid));
> - __asm__("movq %%rax, %%rdi ; movq %0, %%rax ; movq %1, %%rsi ;"
> - "syscall": : "g" (__NR_kill), "g" (SIGUSR1) :
> - "%rdi", "%rax", "%rsi");
> + pid =3D stub_syscall0(__NR_getpid);
> + stub_syscall2(__NR_kill, pid, SIGUSR1);
> +
> /* sys_sigreturn expects that the stack pointer will be 8 bytes into
> * the signal frame. So, we use the ucontext pointer, which we know
> * already, to get the signal frame pointer, and add 8 to that.
> */
> - __asm__("movq %0, %%rsp": :
> + __asm__("movq %0, %%rsp; movq %1, %%rax ; syscall": :
> "g" ((unsigned long) container_of(uc, struct rt_sigframe,
> - uc) + 8));
> - __asm__("movq %0, %%rax ; syscall" : : "g" (__NR_rt_sigreturn));
> + uc) + 8),
> + "g" (__NR_rt_sigreturn));
> }
>
> -
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Cheers,
Dick Johnson
Penguin : Linux version 2.6.13.4 on an i686 machine (5589.44 BogoMips).
Warning : 98.36% of all statistics are fiction.
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