Re: [PATCH v6 1/6] arm64: Add HAVE_REGS_AND_STACK_ACCESS_API feature

From: David Long
Date: Fri May 22 2015 - 13:05:22 EST

On 05/21/15 13:55, Catalin Marinas wrote:
On Wed, May 20, 2015 at 11:29:24PM -0400, David Long wrote:
On 05/20/15 09:39, Catalin Marinas wrote:
On Mon, Apr 20, 2015 at 04:19:42PM -0400, David Long wrote:
diff --git a/arch/arm64/include/uapi/asm/ptrace.h b/arch/arm64/include/uapi/asm/ptrace.h
index 6913643..58c0223 100644
--- a/arch/arm64/include/uapi/asm/ptrace.h
+++ b/arch/arm64/include/uapi/asm/ptrace.h
@@ -61,6 +61,42 @@

#ifndef __ASSEMBLY__

+#define ARM_pstate pstate
+#define ARM_pc pc
+#define ARM_sp sp
+#define ARM_lr regs[30]
+#define ARM_fp regs[29]
+#define ARM_x28 regs[28]
+#define ARM_x27 regs[27]
+#define ARM_x26 regs[26]
+#define ARM_x25 regs[25]
+#define ARM_x24 regs[24]
+#define ARM_x23 regs[23]
+#define ARM_x22 regs[22]
+#define ARM_x21 regs[21]
+#define ARM_x20 regs[20]
+#define ARM_x19 regs[19]
+#define ARM_x18 regs[18]
+#define ARM_ip1 regs[17]
+#define ARM_ip0 regs[16]
+#define ARM_x15 regs[15]
+#define ARM_x14 regs[14]
+#define ARM_x13 regs[13]
+#define ARM_x12 regs[12]
+#define ARM_x11 regs[11]
+#define ARM_x10 regs[10]
+#define ARM_x9 regs[9]
+#define ARM_x8 regs[8]
+#define ARM_x7 regs[7]
+#define ARM_x6 regs[6]
+#define ARM_x5 regs[5]
+#define ARM_x4 regs[4]
+#define ARM_x3 regs[3]
+#define ARM_x2 regs[2]
+#define ARM_x1 regs[1]
+#define ARM_x0 regs[0]
+#define ARM_ORIG_x0 orig_x0

I replied some time ago on this part. I don't see the point these
macros.

I replied belatedly on April 20 saying what I did matches (more or less) how
it's done on various other platforms, including arm and powerpc.
It looks like this comes from the pt_regs structure defining the
registers as an array instead of a list of structure fields. It looks
to me like that design choice is pretty widely depended upon now and
would be quite disruptive to change. It also seems to me a relatively
clean way to do it on systems with a uniform register set.

I see why we need to cope with the regs[] array but why do we need these
definitions in a uapi file?


I expect Sandeepa did it that way because it's the way it's done in other architectures. I see your point though, these definitions are only referenced in a macro that's defined and used only in ptrace.c. I can easily move them there.

+
/*
* User structures for general purpose, floating point and debug registers.
*/
diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index d882b83..a889f79 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -48,6 +48,122 @@
#define CREATE_TRACE_POINTS
#include <trace/events/syscalls.h>

+struct pt_regs_offset {
+ const char *name;
+ int offset;
+};
+
+#define REG_OFFSET_NAME(r) \
+ {.name = #r, .offset = offsetof(struct pt_regs, ARM_##r)}

Can you not just use "offsetof(struct pt_regs, r)" here? That would be
the same as x86, powerpc.

The registers (except for pc, pstate, and sp) are not separate structure
fields, they are slots in a single array. To reference them the symbolic
name has to be converted to an index (integer register number) somehow.

Can we not keep them local to this file, say __reg_x0 etc. (something to
make it clear they are for internal use)?


As above we can make it local to the file. Given that I don't think there's a need to chance ARM_x* to __reg_x* though, is there? Either way, no problem.

-dl

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