diff mbox

[v2,3/5,nios2] fix register save offset for signal handler trampolines

Message ID 55417801.5070507@codesourcery.com
State New
Headers show

Commit Message

Sandra Loosemore April 30, 2015, 12:32 a.m. UTC
It was requested that I split the patch previously posted here:

https://sourceware.org/ml/gdb-patches/2015-04/msg00907.html

into two parts.  This is the first part.  I also expanded the comments 
to indicate how the register save offset magic number was calculated.

OK to commit now?

-Sandra

Comments

Yao Qi May 8, 2015, 9:30 a.m. UTC | #1
Sandra Loosemore <sandra@codesourcery.com> writes:

> It was requested that I split the patch previously posted here:
>
> https://sourceware.org/ml/gdb-patches/2015-04/msg00907.html
>
> into two parts.  This is the first part.  I also expanded the comments
> to indicate how the register save offset magic number was calculated.

Hi Sandra,
The reason I suggest to describe how this magic number is calculated in
this mail https://sourceware.org/ml/gdb-patches/2015-04/msg01038.html is
to make the code more maintainable.  Supposing some one changes the
offset in linux kernel in the future, we'll quickly know how to update
the magic number.  However, I don't insist on this...

>
> OK to commit now?

Yes, it is OK.
diff mbox

Patch

diff --git a/gdb/nios2-linux-tdep.c b/gdb/nios2-linux-tdep.c
index b829569..0a837b0 100644
--- a/gdb/nios2-linux-tdep.c
+++ b/gdb/nios2-linux-tdep.c
@@ -114,7 +114,25 @@  nios2_iterate_over_regset_sections (struct gdbarch *gdbarch,
 }
 
 /* Initialize a trad-frame cache corresponding to the tramp-frame.
-   FUNC is the address of the instruction TRAMP[0] in memory.  */
+   FUNC is the address of the instruction TRAMP[0] in memory.
+
+   This ABI is not documented.  It corresponds to rt_setup_ucontext in
+   the kernel arch/nios2/kernel/signal.c file.
+
+   The key points are:
+   - The kernel creates a trampoline at the hard-wired address 0x1044.
+   - The stack pointer points to an object of type struct rt_sigframe.
+     The definition of this structure is not exported from the kernel.
+     The register save area is located at offset 152 bytes (as determined
+     by inspection of the stack contents in the debugger), and the
+     registers are saved as r1-r23, ra, fp, gp, ea, sp.
+
+   This interface was implemented with kernel version 3.19 (the first
+   official mainline kernel).  Older unofficial kernel versions used
+   incompatible conventions; we do not support those here.  */
+
+#define NIOS2_SIGRETURN_TRAMP_ADDR 0x1044
+#define NIOS2_SIGRETURN_REGSAVE_OFFSET 152
 
 static void
 nios2_linux_rt_sigreturn_init (const struct tramp_frame *self,
@@ -122,7 +140,8 @@  nios2_linux_rt_sigreturn_init (const struct tramp_frame *self,
 			       struct trad_frame_cache *this_cache,
 			       CORE_ADDR func)
 {
-  CORE_ADDR base = func + 41 * 4;
+  CORE_ADDR sp = get_frame_register_unsigned (next_frame, NIOS2_SP_REGNUM);
+  CORE_ADDR base = sp + NIOS2_SIGRETURN_REGSAVE_OFFSET;
   int i;
 
   for (i = 0; i < 23; i++)