32-bit gcore on amd64

[Andrew Cagney <cagney at gnu dot org>]

This is more questions than answers.  I'm trying to figure out how GDB 
should generate 32-bit core files on amd64 (i.e., get gmake check 
'RUNTESTFLAGS=--target_board=unix/-m32 gcore.exp' to pass).  The problem 
is, everything I look at feels wrong.

Here's the first backtrace:

#0  amd64_collect_native_gregset (regcache=0x808410, gregs=0x7fbfffead0,
    regnum=-1) at /home/cygnus/cagney/GDB/src/gdb/amd64-nat.c:124
#1  0x0000000000450e16 in fill_gregset (gregsetp=0x808410, 
regnum=-1073747248)
    at /home/cygnus/cagney/GDB/src/gdb/x86-64-linux-nat.c:126
#2  0x000000000045803d in linux_do_thread_registers (obfd=0x87fc90, ptid=
      {pid = 10494, lwp = 10494, tid = 0}, note_data=0x8b0960 "\005",
    note_size=0x7fbfffed8c) at 
/home/cygnus/cagney/GDB/src/gdb/linux-proc.c:180

This function is asking fill_gregset to populate an amd64 gregset_t.  I 
think it should be asking for the 32-bit gregset_t to be filled in.

#3  0x0000000000458227 in linux_do_registers (obfd=0x87fc90, ptid=
      {pid = 10494, lwp = 0, tid = 0}, note_data=0x8b0960 "\005",
    note_size=0x7fbfffed8c) at 
/home/cygnus/cagney/GDB/src/gdb/linux-proc.c:250
#4  0x00000000004583f8 in linux_make_note_section (obfd=0x87fc90,
    note_size=0x7fbfffed8c) at 
/home/cygnus/cagney/GDB/src/gdb/linux-proc.c:302

Here, I'm thinking that if this is to be portable, this would have to be 
an architecture method (also parameterized with the target).

#5  0x00000000004594d2 in gcore_command (args=0x0, from_tty=-1073747248)
    at /home/cygnus/cagney/GDB/src/gdb/gcore.c:80

Now the second backtrace:

#0  elfcore_write_prstatus (abfd=0x87fc90, buf=0x8b0960 "\005",
    bufsiz=0x7fbfffed8c, pid=10494, cursig=5, gregs=0x7fbfffead0)
    at /home/cygnus/cagney/GDB/src/bfd/elf.c:7163

This function totally assumes that it's creating a 64-bit note section. 
How does BFD figure out that it should instead use 32-bit note code?

#1  0x0000000000458058 in linux_do_thread_registers (obfd=0x87fc90, ptid=
      {pid = 10494, lwp = 10494, tid = 0}, note_data=0x8b0960 "\005",
    note_size=0x7fbfffed8c) at 
/home/cygnus/cagney/GDB/src/gdb/linux-proc.c:181
#2  0x0000000000458227 in linux_do_registers (obfd=0x87fc90, ptid=
      {pid = 10494, lwp = 0, tid = 0}, note_data=0x8b0960 "\005",
    note_size=0x7fbfffed8c) at 
/home/cygnus/cagney/GDB/src/gdb/linux-proc.c:250
#3  0x00000000004583f8 in linux_make_note_section (obfd=0x87fc90,
    note_size=0x7fbfffed8c) at 
/home/cygnus/cagney/GDB/src/gdb/linux-proc.c:302
#4  0x00000000004594d2 in gcore_command (args=0x0, from_tty=-1073747032)
    at /home/cygnus/cagney/GDB/src/gdb/gcore.c:80

Andrew

As a somewhat amazing PS: bigcore.exp does pass 32-bit mode on AMD-64 
->> the 32-bit read path is ok.