Re: [ppc64-linux]: register CONVERT_FROM_FUNC_PTR_ADDR method

Jim Blandy
2003-06-12T21:11:23Z

Kevin Buettner <kevinb@redhat.com> writes:

> On Jun 11, 3:53am, Jim Blandy wrote:
>
> > 2003-06-11 Jim Blandy <jimb@redhat.com>
> >
> > * ppc-linux-tdep.c (ppc64_linux_convert_from_func_ptr_addr): New
> > function.
> > (ppc_linux_init_abi): Register it as the
> > CONVERT_FROM_FUNC_PTR_ADDR method under the PPC64 Linux ABI.
>
> Okay, but could you revise the comment to not mention RS/6000 and
> to make it clear that the representation in question only pertains
> to the 64-bit ABI?

How's this?

2003-06-11 Jim Blandy <jimb@redhat.com>

* ppc-linux-tdep.c (ppc64_linux_convert_from_func_ptr_addr): New
function.
(ppc_linux_init_abi): Register it as the
CONVERT_FROM_FUNC_PTR_ADDR method under the PPC64 Linux ABI.

Index: gdb/ppc-linux-tdep.c
===================================================================
RCS file: /cvs/src/src/gdb/ppc-linux-tdep.c,v
retrieving revision 1.28.8.17
diff -c -r1.28.8.17 ppc-linux-tdep.c
*** gdb/ppc-linux-tdep.c 12 Jun 2003 21:09:22 -0000 1.28.8.17
--- gdb/ppc-linux-tdep.c 12 Jun 2003 21:09:42 -0000
***************
*** 894,899 ****
--- 894,934 ----
}

+ /* Support for CONVERT_FROM_FUNC_PTR_ADDR(ADDR) on PPC64 Linux.
+
+ Usually a function pointer's representation is simply the address
+ of the function. On Linux on the 64-bit PowerPC however, a function
+ pointer is represented by a pointer to a TOC entry. This TOC entry
+ contains three words, the first word is the address of the
+ function, the second word is the TOC pointer (r2), and the third
+ word is the static chain value. Throughout GDB it is currently
+ assumed that a function pointer contains the address of the
+ function, which is not easy to fix. In addition, the conversion of
+ a function address to a function pointer would require allocation
+ of a TOC entry in the inferior's memory space, with all its
+ drawbacks. To be able to call C++ virtual methods in the inferior
+ (which are called via function pointers), find_function_addr uses
+ this function to get the function address from a function
+ pointer. */
+
+ /* Return real function address if ADDR (a function pointer) is in the data
+ space and is therefore a special function pointer. */
+
+ static CORE_ADDR
+ ppc64_linux_convert_from_func_ptr_addr (CORE_ADDR addr)
+ {
+ struct obj_section *s;
+
+ s = find_pc_section (addr);
+ if (s && s->the_bfd_section->flags & SEC_CODE)
+ return addr;
+
+ /* ADDR is in the data space, so it's a pointer to a descriptor, not
+ the entry point. */
+ return ppc64_desc_entry_point (addr);
+ }
+
+
/* On 64-bit PowerPC Linux, the ELF header's e_entry field is the
address of a function descriptor for the entry point function, not
the actual entry point itself. So to find the actual address at
***************
*** 1027,1032 ****
--- 1062,1072 ----

if (tdep->wordsize == 8)
{
+ /* Handle PPC64 Linux function pointers (which are really
+ function descriptors). */
+ set_gdbarch_convert_from_func_ptr_addr
+ (gdbarch, ppc64_linux_convert_from_func_ptr_addr);
+
set_gdbarch_call_dummy_address (gdbarch, ppc64_call_dummy_address);

set_gdbarch_in_solib_call_trampoline