[binutils-gdb] MIPS: Don't use a 32-bit BFD architecture with a 64-bit ABI

[Maciej W.Rozycki <macro at sourceware dot org>]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=c5196c9298b7df29652c0ebe24a43ac6c9c76b0d

commit c5196c9298b7df29652c0ebe24a43ac6c9c76b0d
Author: Maciej W. Rozycki <macro@mips.com>
Date:   Mon Feb 26 19:43:17 2018 +0000

    MIPS: Don't use a 32-bit BFD architecture with a 64-bit ABI
    
    Select `bfd_mach_mips4000', which corresponds to the MIPS III ISA, the
    earlies with 64-bit support, whenever a 32-bit BFD architecture has been
    chosen to use with a 64-bit ABI.  The situation can happen in a few
    cases:
    
    1. When the user has used `set architecture' or `set mips abi' commands
       to override automatic selection and then starts a debug session by
       requesting to run, attach or connect to a target.
    
    2. In native debugging when reattaching to a previously debugged process
       where the program to be debugged has been since discarded, as
       observed with:
    
    FAIL: gdb.base/attach.exp: attach2, with no file (GDB internal error)
    
       in n32 and n64 regression testing.
    
    3. In remote debugging with a non-XML debug stub when discarding the
       program to be debugged while connected to the remote target, as
       observed with:
    
    FAIL: gdb.base/break-unload-file.exp: cmdline: always-inserted on: break: file (GDB internal error)
    
       in n32 and n64 regression testing.
    
    In the latter two cases the ABI, quite rightfully, is retained while the
    program to be debugged is discarded.  This is because in that case the
    ABI previously determined is carried over along with `gdbarch' in use,
    which is retained.  The BFD architecture is however discarded and the
    default then applies, because it is not attached to `gdbarch'.
    
    In all these cases we trip with an internal error message as follows:
    
    .../gdb/mips-tdep.c:766: internal-error: bad register size
    A problem internal to GDB has been detected,
    further debugging may prove unreliable.
    Quit this debugging session? (y or n) n
    
    This is a bug, please report it.  For instructions, see:
    <http://www.gnu.org/software/gdb/bugs/>.
    
    coming from `mips_pseudo_register_read', because the raw register width
    inferred from the BFD architecture turns out to be 4 for the general
    registers while the cooked register width inferred from the ABI in
    effect is 8.
    
    We do not hit this internal error in remote debugging with an XML debug
    stub, because in that case raw register width information is passed by
    the stub along with the XML target description.
    
    Ultimately I think we ought to make the BFD architecture sticky like the
    ABI, however in the interim this simple fix will do, removing the error
    across all three cases.  The case where the user has used `set mips abi'
    or `set architecture' commands has to be handled anyway, and although a
    more sophisticated solution could be envisaged, such as reporting an
    error with the respective `set' command, I think this is too much of a
    corner case to bother.
    
    	gdb/
    	* mips-tdep.c (mips_gdbarch_init): Don't use a 32-bit BFD
    	architecture with a 64-bit ABI.

Diff:
---
 gdb/ChangeLog   | 5 +++++
 gdb/mips-tdep.c | 8 ++++++++
 2 files changed, 13 insertions(+)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index fd79872..b9a9bcd 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,10 @@
 2018-02-26  Maciej W. Rozycki  <macro@mips.com>
 
+	* mips-tdep.c (mips_gdbarch_init): Don't use a 32-bit BFD
+	architecture with a 64-bit ABI.
+
+2018-02-26  Maciej W. Rozycki  <macro@mips.com>
+
 	* gdb/mips-tdep.c (mips_gdbarch_init): Reorder ABI determination
 	ahead of target description loading.
 
diff --git a/gdb/mips-tdep.c b/gdb/mips-tdep.c
index ae747ff..f9f84c4 100644
--- a/gdb/mips-tdep.c
+++ b/gdb/mips-tdep.c
@@ -8185,6 +8185,14 @@ mips_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
     fprintf_unfiltered (gdb_stdlog, "mips_gdbarch_init: mips_abi = %d\n",
 			mips_abi);
 
+  /* Make sure we don't use a 32-bit architecture with a 64-bit ABI.  */
+  if (mips_abi != MIPS_ABI_EABI32
+      && mips_abi != MIPS_ABI_O32
+      && info.bfd_arch_info != NULL
+      && info.bfd_arch_info->arch == bfd_arch_mips
+      && info.bfd_arch_info->bits_per_word < 64)
+    info.bfd_arch_info = bfd_lookup_arch (bfd_arch_mips, bfd_mach_mips4000);
+
   /* Determine the default compressed ISA.  */
   if ((elf_flags & EF_MIPS_ARCH_ASE_MICROMIPS) != 0
       && (elf_flags & EF_MIPS_ARCH_ASE_M16) == 0)