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Re: PATCH: Add x32 arch_prctl support
On Fri, May 18, 2012 at 11:35 AM, Roland McGrath <roland@hack.frob.com> wrote:
>
>> + ?unsigned long long base_addr;
>> + ?unsigned long *addr_saved;
>
> This is probably going to get a "might be used uninitialized" warning.
Yes. Should I silence it?
> Anyway, I think it's cleaner to pass an 'unsigned long long int' (or
> uint64_t) to the syscall, since that's what it is in the kernel.
> Might as well just make it:
I thought about it and decided against it since it will require
special treatment for x32 when it is used.
>> +#include <errno.h>
>> +#include <sys/types.h>
>> +#define ptrace __redirect_ptrace
>> +#include <sys/ptrace.h>
>> +#undef ptrace
>> +#include <sys/syscall.h>
>> +#include <sysdep.h>
>
> If this funny business were warranted, it would need some comments.
> But it's not. ?Just use stdarg like linux/ptrace.c does.
>
>> +#ifndef PTRACE_ARCH_PRCTL
>> +#define PTRACE_ARCH_PRCTL ? ? ?30
>> +#endif
>
> This should never be required. ?Just add it to ptrace.h.
PTRACE_ARCH_PRCTL is x86 specific and is only used by GDB,
GDB has #ifdef to define it, which will never be removed. If we add
it to ptrace.h, I have to add it a new ptrace for x86-64. I don't think
we should do it.
>> + switch ((int) request)
>> + {
>
> There's no need to cast to int when you have a default case anyway.
I need it if PTRACE_ARCH_PRCTL isn't in x86-64 ptrace.h.
>
> But actually, PTRACE_ARCH_PRCTL should be entirely obsolete anyway.
> You should just drop it from the x32 kernel. ?Since many kernel
> versions ago, you can just use the fs_base and gs_base fields in
> user_regs_struct via the other ptrace calls.
>
That is true. However, since it is used in GDB today, I need it
to support it for x32. Here is the patch. Does it look OK?
Thanks.
--
H.J.
----
* sysdeps/unix/sysv/linux/x86_64/x32/Makefile (sysdep_routines):
Add arch_prctl.
* sysdeps/unix/sysv/linux/x86_64/x32/arch_prctl.c: New file.
* sysdeps/unix/sysv/linux/x86_64/x32/ptrace.c: Likewise.
diff --git a/sysdeps/unix/sysv/linux/x86_64/x32/Makefile
b/sysdeps/unix/sysv/linux/x86_64/x32/Makefile
index 5f77df7..aa78238 100644
--- a/sysdeps/unix/sysv/linux/x86_64/x32/Makefile
+++ b/sysdeps/unix/sysv/linux/x86_64/x32/Makefile
@@ -1,3 +1,7 @@
+ifeq ($(subdir),misc)
+sysdep_routines += arch_prctl
+endif
+
ifeq ($(subdir),posix)
sysdep_routines += getcpu sched_getcpu-static
endif
diff --git a/sysdeps/unix/sysv/linux/x86_64/x32/arch_prctl.c
b/sysdeps/unix/sysv/linux/x86_64/x32/arch_prctl.c
new file mode 100644
index 0000000..44c100b
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/x86_64/x32/arch_prctl.c
@@ -0,0 +1,64 @@
+/* arch_prctl call for Linux/x32.
+ Copyright (C) 2012 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <http://www.gnu.org/licenses/>. */
+
+#include <errno.h>
+#include <sys/prctl.h>
+#include <sys/syscall.h>
+#include <sysdep.h>
+
+/* Since x32 arch_prctl stores 32-bit base address of segment register %fs
+ and %gs as unsigned 64-bit value via ARCH_GET_FS and ARCH_GET_GS, we
+ use a local unsigned 64-bit variable to hold the base address and copy
+ it to ADDR after arch_prctl return. */
+
+int
+__arch_prctl (int code, uintptr_t *addr)
+{
+ int res;
+ uint64_t addr64;
+ uintptr_t *addr_saved;
+
+ switch (code)
+ {
+ case ARCH_GET_FS:
+ case ARCH_GET_GS:
+ addr_saved = addr;
+ addr = (uintptr_t *) &addr64;
+ break;
+ }
+
+ res = INLINE_SYSCALL (arch_prctl, 2, code, addr);
+ if (res == 0)
+ switch (code)
+ {
+ case ARCH_GET_FS:
+ case ARCH_GET_GS:
+ /* Check for a large value that overflows. */
+ if ((uintptr_t) addr64 != addr64)
+ {
+ __set_errno (EOVERFLOW);
+ return -1;
+ }
+ *addr_saved = (uintptr_t) addr64;
+ break;
+ }
+
+ return res;
+}
+
+weak_alias (__arch_prctl, arch_prctl)
diff --git a/sysdeps/unix/sysv/linux/x86_64/x32/ptrace.c
b/sysdeps/unix/sysv/linux/x86_64/x32/ptrace.c
new file mode 100644
index 0000000..c026307
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/x86_64/x32/ptrace.c
@@ -0,0 +1,107 @@
+/* ptrace call for Linux/x32.
+ Copyright (C) 2012 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <http://www.gnu.org/licenses/>. */
+
+#include <errno.h>
+#include <sys/types.h>
+#define ptrace __redirect_ptrace
+#include <sys/ptrace.h>
+#undef ptrace
+#include <sys/syscall.h>
+#include <sysdep.h>
+
+/* PTRACE_ARCH_PRCTL is specific to x86 kernel and is only used by GDB. */
+#ifndef PTRACE_ARCH_PRCTL
+# define PTRACE_ARCH_PRCTL 30
+#endif
+
+/* Since x32 ptrace stores 32-bit base address of segment register %fs
+ and %gs as unsigned 64-bit value via ARCH_GET_FS and ARCH_GET_GS with
+ PTRACE_ARCH_PRCTL, we use a local unsigned 64-bit variable to hold
+ the base address and copy it to ADDR after ptrace return.
+
+ We don't use
+
+ long int ptrace (enum __ptrace_request __request, ...);
+
+ since x32 passes all 4 parameters in registers, which is the same
+ as the non-stdarg call. The generated code is much simpler.
+ */
+
+long int
+ptrace (enum __ptrace_request request, pid_t pid, void *addr, void *data)
+{
+ long res, ret;
+ unsigned long long base_addr;
+ unsigned long *addr_saved;
+
+ switch ((int) request)
+ {
+ case PTRACE_PEEKTEXT:
+ case PTRACE_PEEKDATA:
+ case PTRACE_PEEKUSER:
+ /* Pass the address of return data to kernel. */
+ data = &ret;
+ break;
+
+ case PTRACE_ARCH_PRCTL:
+ switch ((int) data)
+ {
+ case ARCH_GET_FS:
+ case ARCH_GET_GS:
+ addr_saved = (unsigned long *) addr;
+ addr = &base_addr;
+ break;
+
+ default:
+ break;
+ }
+ break;
+
+ default:
+ break;
+ }
+
+ res = INLINE_SYSCALL (ptrace, 4, request, pid, addr, data);
+ if (res >= 0)
+ switch ((int) request)
+ {
+ case PTRACE_PEEKTEXT:
+ case PTRACE_PEEKDATA:
+ case PTRACE_PEEKUSER:
+ __set_errno (0);
+ return ret;
+
+ case PTRACE_ARCH_PRCTL:
+ switch ((int) data)
+ {
+ case ARCH_GET_FS:
+ case ARCH_GET_GS:
+ *addr_saved = (unsigned long) base_addr;
+ break;
+
+ default:
+ break;
+ }
+ break;
+
+ default:
+ break;
+ }
+
+ return res;
+}