[patch v2 4/4] ptrace: Add support for generic PTRACE_GETREGSET/PTRACE_SETREGSET

Suresh Siddha
2010-02-09T20:28:37Z

[-- Attachment #1: ptrace_support_for_xstate.patch --]
[-- Type: text/plain, Size: 8012 bytes --]

Generic support for PTRACE_GETREGSET/PTRACE_SETREGSET commands which
export the regsets supported by each architecture using the correponding
NT_* types.

'addr' parameter for the ptrace system call encode the REGSET type and
the buffer length. 'data' parameter points to the user buffer.

ptrace(PTRACE_GETREGSET/PTRACE_SETREGSET, pid,
(NT_TYPE << 20) | buf_length, buf);

For more information on how to use this API by users like debuggers and core
dump for accessing xstate registers, etc., please refer to comments in
arch/x86/include/asm/ptrace-abi.h

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Acked-by: Hongjiu Lu <hjl.tools@gmail.com>
---
arch/x86/include/asm/ptrace-abi.h | 51 ++++++++++++++++++++++++++++++++++++++
include/linux/elf.h | 25 +++++++++++++++++-
include/linux/ptrace.h | 14 ++++++++++
kernel/ptrace.c | 34 +++++++++++++++++++++++++
4 files changed, 122 insertions(+), 2 deletions(-)

Index: tip/include/linux/ptrace.h
===================================================================
--- tip.orig/include/linux/ptrace.h
+++ tip/include/linux/ptrace.h
@@ -26,6 +26,18 @@
#define PTRACE_GETEVENTMSG 0x4201
#define PTRACE_GETSIGINFO 0x4202
#define PTRACE_SETSIGINFO 0x4203
+#define PTRACE_GETREGSET 0x4204
+#define PTRACE_SETREGSET 0x4205
+
+/*
+ * First 20 bits of the addr in the PTRACE_GETREGSET/PTRACE_SETREGSET requests
+ * are reserved for communicating the user buffer size and the remaining 12 bits
+ * are reserved for the NT_* types (defined in include/linux/elf.h) which
+ * indicate the regset that the ptrace user is interested in.
+ */
+#define PTRACE_REGSET_BUF_SIZE(addr) (addr & 0xfffff)
+#define PTRACE_REGSET_TYPE(addr) ((addr >> 20) & 0xfff)
+#define NOTE_TO_REGSET_TYPE(note) (note & 0xfff)

/* options set using PTRACE_SETOPTIONS */
#define PTRACE_O_TRACESYSGOOD 0x00000001
@@ -114,6 +126,8 @@ static inline void ptrace_unlink(struct

int generic_ptrace_peekdata(struct task_struct *tsk, long addr, long data);
int generic_ptrace_pokedata(struct task_struct *tsk, long addr, long data);
+int generic_ptrace_regset(struct task_struct *child, long request, long addr,
+ long data);

/**
* task_ptrace - return %PT_* flags that apply to a task
Index: tip/kernel/ptrace.c
===================================================================
--- tip.orig/kernel/ptrace.c
+++ tip/kernel/ptrace.c
@@ -22,6 +22,7 @@
#include <linux/pid_namespace.h>
#include <linux/syscalls.h>
#include <linux/uaccess.h>
+#include <linux/regset.h>

/*
@@ -573,6 +574,11 @@ int ptrace_request(struct task_struct *c
return 0;
return ptrace_resume(child, request, SIGKILL);

+#ifdef PTRACE_EXPORT_REGSET
+ case PTRACE_GETREGSET:
+ case PTRACE_SETREGSET:
+ return generic_ptrace_regset(child, request, addr, data);
+#endif
default:
break;
}
@@ -664,6 +670,34 @@ int generic_ptrace_pokedata(struct task_
return (copied == sizeof(data)) ? 0 : -EIO;
}

+#ifdef PTRACE_EXPORT_REGSET
+int generic_ptrace_regset(struct task_struct *child, long request, long addr,
+ long data)
+{
+ const struct user_regset_view *view = task_user_regset_view(child);
+ unsigned int buf_size = PTRACE_REGSET_BUF_SIZE(addr);
+ int setno;
+
+ for (setno = 0; setno < view->n; setno++) {
+ const struct user_regset *regset = &view->regsets[setno];
+ if (NOTE_TO_REGSET_TYPE(regset->core_note_type) !=
+ PTRACE_REGSET_TYPE(addr))
+ continue;
+
+ if (request == PTRACE_GETREGSET)
+ return copy_regset_to_user(child, view, setno, 0,
+ buf_size,
+ (void __user *) data);
+ else if (request == PTRACE_SETREGSET)
+ return copy_regset_from_user(child, view, setno, 0,
+ buf_size,
+ (void __user *) data);
+ }
+
+ return -EIO;
+}
+#endif
+
#if defined CONFIG_COMPAT
#include <linux/compat.h>

Index: tip/arch/x86/include/asm/ptrace-abi.h
===================================================================
--- tip.orig/arch/x86/include/asm/ptrace-abi.h
+++ tip/arch/x86/include/asm/ptrace-abi.h
@@ -139,4 +139,54 @@ struct ptrace_bts_config {
Returns number of BTS records drained.
*/

+/*
+ * The extended register state using xsave/xrstor infrastructure can be
+ * be read and set by the user using the following ptrace command.
+ *
+ * ptrace(PTRACE_GETREGSET/PTRACE_SETREGSET, pid,
+ * (NT_X86_XSTATE << 20) | xstate_buf_length, xstate_buf);
+ *
+ * The structure layout used for the xstate_buf is same as
+ * the memory layout of xsave used by the processor (except for the bytes
+ * 464..511, which can be used by the software) and hence the size
+ * of this structure varies depending on the features supported by the processor
+ * and OS. The size of the structure that users need to use can be obtained by
+ * doing:
+ * cpuid_count(0xd, 0, &eax, &ptrace_xstateregs_struct_size, &ecx, &edx);
+ * i.e., cpuid.(eax=0xd,ecx=0).ebx will be the size that user (debuggers, etc.)
+ * need to use.
+ *
+ * The format of this structure will be like:
+ * struct {
+ * fxsave_bytes[0..463]
+ * sw_usable_bytes[464..511]
+ * xsave_hdr_bytes[512..575]
+ * avx_bytes[576..831]
+ * future_state etc
+ * }
+ *
+ * The same memory layout will be used for the core-dump NT_X86_XSTATE
+ * note representing the xstate registers.
+ *
+ * For now, only the first 8 bytes of the sw_usable_bytes[464..471] will
+ * be used and will be set to OS enabled xstate mask (which is same as the
+ * 64bit mask returned by the xgetbv's xCR0). Users (analyzing core dump
+ * remotely, etc.) can use this mask as well as the mask saved in the
+ * xstate_hdr bytes and interpret what states the processor/OS supports
+ * and what states are in modified/initialized conditions for the
+ * particular process/thread.
+ *
+ * Also when the user modifies certain state FP/SSE/etc through this
+ * PTRACE_SETXSTATEREGS, they must ensure that the xsave_hdr.xstate_bv
+ * bytes[512..519] of the above memory layout are updated correspondingly.
+ * i.e., for example when FP state is modified to a non-init state,
+ * xsave_hdr.xstate_bv's bit 0 must be set to '1', when SSE is modified to
+ * non-init state, xsave_hdr.xstate_bv's bit 1 must to be set to '1', etc.
+ */
+
+/*
+ * Enable PTRACE_GETREGSET/PTRACE_SETREGSET interface
+ */
+#define PTRACE_EXPORT_REGSET
+
#endif /* _ASM_X86_PTRACE_ABI_H */
Index: tip/include/linux/elf.h
===================================================================
--- tip.orig/include/linux/elf.h
+++ tip/include/linux/elf.h
@@ -349,7 +349,29 @@ typedef struct elf64_shdr {
#define ELF_OSABI ELFOSABI_NONE
#endif

-/* Notes used in ET_CORE */
+/*
+ * Notes used in ET_CORE. Architectures export some of the arch register sets
+ * using the corresponding note types via ptrace
+ * PTRACE_GETREGSET/PTRACE_SETREGSET requests.
+ *
+ * For example,
+ * long addr = (NT_X86_XSTATE << 20 | buf_length);
+ * ptrace(PTRACE_GETREGSET, pid, addr, buf);
+ *
+ * will obtain the x86 extended register state of the pid.
+ *
+ * On 32bit architectures, addr argument is 32bits wide and encodes the length
+ * of the buffer in the first 20 bits, followed by NT_* type encoded in the
+ * remaining 12 bits, representing an unique regset.
+ *
+ * Hence on 32bit architectures, NT_PRXFPREG (0x46e62b7f) will be seen as 0xb7f
+ * and we can't allocate 0xb7f to any other note.
+ *
+ * All the other existing NT_* types fall with in the 12 bits and we have
+ * plenty of room for more NT_* types. For now, on all architectures
+ * we use first 20 bits of the addr for the buffer size and the next 12 bits for
+ * the NT_* type representing the corresponding regset.
+ */
#define NT_PRSTATUS 1
#define NT_PRFPREG 2
#define NT_PRPSINFO 3
@@ -364,7 +386,6 @@ typedef struct elf64_shdr {
#define NT_X86_XSTATE 0x202 /* x86 extended state using xsave */
#define NT_S390_HIGH_GPRS 0x300 /* s390 upper register halves */

-
/* Note header in a PT_NOTE section */
typedef struct elf32_note {
Elf32_Word n_namesz; /* Name size */