[PING^2][PATCH] in_plt_section: support alternate stub section names (was: [PATCH 1/2] MIPS: Compressed PLT/stubs support)

["Maciej W. Rozycki" <macro@codesourcery.com>]

Tom,

 I have now recalled that you made this comment about the original version 
of this change:

On Thu, 21 Feb 2013, Tom Tromey wrote:

> Maciej> -/* In SVR4, we recognize a trampoline by it's section name. 
> Maciej> -   That is, if the pc is in a section named ".plt" then we are in
> Maciej> -   a trampoline.  */
> Maciej> +/* In SVR4, we recognize a trampoline by it's section name.  That is,
> Maciej> +   if the pc is in a section named ".plt" then we are in a trampoline.
> Maciej> +   We let targets request an alternative name, this is currently used
> Maciej> +   by the MIPS backend to handle the SVR4 lazy resolution stubs that
> Maciej> +   binutils put into ".MIPS.stubs" instead.  */
> 
> IMO comments like this tend to get stale over time.
> It is better, I think, to describe the function's interface and purpose,
> and leave it to future developers to grep for uses of it, should they
> need to know.

 I have now made the requested update, see below.  Is this version OK to 
apply?

2013-06-20  Maciej W. Rozycki  <macro@codesourcery.com>

	gdb/
	* mips-linux-tdep.c (mips_linux_in_dynsym_stub): Handle
	.MIPS.stubs section like .plt.  Remove unused `name' argument.
	Return 1 rather than the low 16-bit halfword of any instruction
	examined.
	(mips_linux_in_dynsym_resolve_code): Update accordingly.
	* mips-tdep.c (mips_stub_frame_sniffer): Call in_plt_section in
	place of an equivalent hand-coded sequence.
	* objfiles.c (in_plt_section): Reuse the `name' argument as an
	trampoline section name override.

  Maciej

gdb-mips-in-stubs-section.diff
Index: gdb-fsf-trunk-quilt/gdb/mips-linux-tdep.c
===================================================================
--- gdb-fsf-trunk-quilt.orig/gdb/mips-linux-tdep.c	2013-06-19 16:54:49.000000000 +0100
+++ gdb-fsf-trunk-quilt/gdb/mips-linux-tdep.c	2013-06-19 16:55:00.280199593 +0100
@@ -30,6 +30,7 @@
 #include "trad-frame.h"
 #include "tramp-frame.h"
 #include "gdbtypes.h"
+#include "objfiles.h"
 #include "solib.h"
 #include "solib-svr4.h"
 #include "solist.h"
@@ -666,25 +667,34 @@ mips_linux_core_read_description (struct
 
 
 /* Check the code at PC for a dynamic linker lazy resolution stub.
-   Because they aren't in the .plt section, we pattern-match on the
-   code generated by GNU ld.  They look like this:
+   GNU ld for MIPS has put lazy resolution stubs into a ".MIPS.stubs"
+   section uniformly since version 2.15.  If the pc is in that section,
+   then we are in such a stub.  Before that ".stub" was used in 32-bit
+   ELF binaries, however we do not bother checking for that since we
+   have never had and that case should be extremely rare these days.
+   Instead we pattern-match on the code generated by GNU ld.  They look
+   like this:
 
    lw t9,0x8010(gp)
    addu t7,ra
    jalr t9,ra
    addiu t8,zero,INDEX
 
-   (with the appropriate doubleword instructions for N64).  Also
-   return the dynamic symbol index used in the last instruction.  */
+   (with the appropriate doubleword instructions for N64).  As any lazy
+   resolution stubs in microMIPS binaries will always be in a
+   ".MIPS.stubs" section we only ever verify standard MIPS patterns. */
 
 static int
-mips_linux_in_dynsym_stub (CORE_ADDR pc, char *name)
+mips_linux_in_dynsym_stub (CORE_ADDR pc)
 {
   gdb_byte buf[28], *p;
   ULONGEST insn, insn1;
   int n64 = (mips_abi (target_gdbarch ()) == MIPS_ABI_N64);
   enum bfd_endian byte_order = gdbarch_byte_order (target_gdbarch ());
 
+  if (in_plt_section (pc, ".MIPS.stubs"))
+    return 1;
+
   read_memory (pc - 12, buf, 28);
 
   if (n64)
@@ -742,7 +752,7 @@ mips_linux_in_dynsym_stub (CORE_ADDR pc,
 	return 0;
     }
 
-  return (insn & 0xffff);
+  return 1;
 }
 
 /* Return non-zero iff PC belongs to the dynamic linker resolution
@@ -756,9 +766,10 @@ mips_linux_in_dynsym_resolve_code (CORE_
   if (svr4_in_dynsym_resolve_code (pc))
     return 1;
 
-  /* Pattern match for the stub.  It would be nice if there were a
-     more efficient way to avoid this check.  */
-  if (mips_linux_in_dynsym_stub (pc, NULL))
+  /* Likewise for the stubs.  They live in the .MIPS.stubs section these
+     days, so we check if the PC is within, than fall back to a pattern
+     match.  */
+  if (mips_linux_in_dynsym_stub (pc))
     return 1;
 
   return 0;
Index: gdb-fsf-trunk-quilt/gdb/mips-tdep.c
===================================================================
--- gdb-fsf-trunk-quilt.orig/gdb/mips-tdep.c	2013-06-19 16:54:49.000000000 +0100
+++ gdb-fsf-trunk-quilt/gdb/mips-tdep.c	2013-06-19 16:55:00.280199593 +0100
@@ -3628,12 +3628,7 @@ mips_stub_frame_sniffer (const struct fr
   if (in_plt_section (pc, NULL))
     return 1;
 
-  /* Binutils for MIPS puts lazy resolution stubs into .MIPS.stubs.  */
-  s = find_pc_section (pc);
-
-  if (s != NULL
-      && strcmp (bfd_get_section_name (s->objfile->obfd, s->the_bfd_section),
-		 ".MIPS.stubs") == 0)
+  if (in_plt_section (pc, ".MIPS.stubs"))
     return 1;
 
   /* Calling a PIC function from a non-PIC function passes through a
Index: gdb-fsf-trunk-quilt/gdb/objfiles.c
===================================================================
--- gdb-fsf-trunk-quilt.orig/gdb/objfiles.c	2013-06-19 16:45:58.000000000 +0100
+++ gdb-fsf-trunk-quilt/gdb/objfiles.c	2013-06-20 17:10:59.240259104 +0100
@@ -1410,9 +1410,9 @@ find_pc_section (CORE_ADDR pc)
 }
 
 
-/* In SVR4, we recognize a trampoline by it's section name. 
-   That is, if the pc is in a section named ".plt" then we are in
-   a trampoline.  */
+/* Return non-zero if PC is in a dynamic function call trampoline.  In
+   SVR4, we recognize a trampoline by its section name NAME, or ".plt"
+   if NAME is null.  */
 
 int
 in_plt_section (CORE_ADDR pc, char *name)
@@ -1424,7 +1424,7 @@ in_plt_section (CORE_ADDR pc, char *name
 
   retval = (s != NULL
 	    && s->the_bfd_section->name != NULL
-	    && strcmp (s->the_bfd_section->name, ".plt") == 0);
+	    && strcmp (s->the_bfd_section->name, name ? name : ".plt") == 0);
   return (retval);
 }
 \f