Bug handling zero sized symbols in minsyms.c

[Robert Norton]

Hi,

In minsyms.c:lookup_minimal_symbol_by_pc_section() there is some code
which attempts to prefer symbols with sizes over those with zero size.
This is quite useful[1]. Unfortunately the present code will only work
if there is at most one zero-sized symbol. The fix is around line 503:

 if (MSYMBOL_SIZE (&msymbol[hi]) == 0
   && best_zero_sized == -1)
   {
   	best_zero_sized = hi;
      hi--;          
      continue;      
   }

SHOULD be:

if (MSYMBOL_SIZE (&msymbol[hi]) == 0)
	{
	      if (best_zero_sized == -1)
	        best_zero_sized = hi;
	      hi--;
	      continue;
	}

We keep the highest zero-sized symbol as the best but continue to
iterate backwards until we hit a non-zero-sized symbol or run out of
symbols. It's pretty clear that this is what was originally intended.

I can get copyright assigment for this if required although it seems
pretty trivial...

Cheers,

Robert

[1] In particular it is useful when debugging assembly functions which
have internal labels for loops etc. Without this fix we sometimes get
back a minsym corresponding to an internal label (e.g. a loop) when
really what we wanted was the function symbol. This messes up prologue
analysis and some other things. For example in our GDB port the assembly
file:

.global main
main:
        nop
test2:
        nop
test3:
        nop
.size main,.-main
.type main,@function

results in:

(gdb) info sym test2
main + 8 in section .text
(gdb) info sym test3
test3 in section .text   <----------------- !!!
(gdb) disas main
Dump of assembler code for function main:
0x00000270 <main+0>:     NOP
0x00000278 <main+8>:     NOP
0x00000280 <test3+0>:    NOP    <----------------- !!!
End of assembler dump.

and in a patched version:

(gdb) info sym test2
main + 8 in section .text
(gdb) info sym test3
main + 16 in section .text
(gdb) disas main
Dump of assembler code for function main:
0x00000270 <main+0>:     NOP
0x00000278 <main+8>:     NOP
0x00000280 <main+16>:    NOP
End of assembler dump.

RCS file: /cvs/dev/tools/src/binutils/gdb/minsyms.c,v
retrieving revision 1.3
diff -u -r1.3 minsyms.c
--- minsyms.c   4 Jan 2008 18:33:25 -0000       1.3
+++ minsyms.c   2 Jul 2008 16:36:02 -0000
@@ -503,10 +503,10 @@
                     symbol isn't an object or function (e.g. a
                     label), or it may just mean that the size was not
                     specified.  */
-                 if (MSYMBOL_SIZE (&msymbol[hi]) == 0
-                     && best_zero_sized == -1)
+                 if (MSYMBOL_SIZE (&msymbol[hi]) == 0)
                    {
-                     best_zero_sized = hi;
+                     if (best_zero_sized == -1)
+                       best_zero_sized = hi;
                      hi--;
                      continue;
                    }