Re: [RFA] x86_64_skip_prologue

[Michal Ludvig <mludvig at suse dot cz>]

Kevin Buettner wrote:
>>3) Now pc points to the first line of the sourcecode of the function 
>>(usually opening '{'). If the next line with debuginfo has pc within 
>>bounds of this function, we will return this pc instead.
> 
> You might want to take a look at some of the other prologue analyzers.
> In particular, you might want to consider calling find_pc_line() instead
> of accessing the data structures directly.

Most of other *_skip_prologue functions pretend, that prolog is an 
always-the-same sequence of instructions, what is not the case on 
x86-64. I can't see an approach other than the one I have chosen.
Of course I can use other structures and maybe some macros, but the 
concept will remain. Or is there another way?

Why should I preferably use find_pc_line()? It gives me the same symtab 
as find_pc_symtab() does... Anyway I have rewritten the code to use it.

> BTW, you might want to run your code through indent.

Sorry, I'm not yet used to follow GNU coding style. Hopefully now it is 
better ;-)
Michal Ludvig
-- 
* SuSE CR, s.r.o     * mludvig@suse.cz
* +420 2 9654 5373   * http://www.suse.cz
Index: x86-64-tdep.c
===================================================================
RCS file: /cvs/src/src/gdb/x86-64-tdep.c,v
retrieving revision 1.10
diff -c -3 -p -r1.10 x86-64-tdep.c
*** x86-64-tdep.c	2002/03/04 11:08:28	1.10
--- x86-64-tdep.c	2002/03/19 15:29:24
*************** x86_64_frameless_function_invocation (st
*** 759,768 ****
    return 0;
  }
  
! /* On x86_64 there are no reasonable prologs.  */
  CORE_ADDR
  x86_64_skip_prologue (CORE_ADDR pc)
  {
    return pc;
  }
  
--- 759,815 ----
    return 0;
  }
  
! /* If a function with debugging information and known beginning
!    is detected, we will return pc of the next line in the source 
!    code. With this approach we effectively skip the prolog.  */
! 
! #define PROLOG_BUFSIZE 4
  CORE_ADDR
  x86_64_skip_prologue (CORE_ADDR pc)
  {
+   int i, firstline, currline;
+   struct symtab_and_line v_sal;
+   struct symbol *v_function;
+   CORE_ADDR salendaddr = 0, endaddr = 0;
+ 
+   /* We will handle only functions beginning with:
+      55          pushq %rbp
+      48 89 e5    movq %rsp,%rbp 
+    */
+   unsigned char prolog_expect[PROLOG_BUFSIZE] = { 0x55, 0x48, 0x89, 0xe5 },
+     prolog_buf[PROLOG_BUFSIZE];
+ 
+   read_memory (pc, (char *) prolog_buf, PROLOG_BUFSIZE);
+ 
+   /* First check, whether pc points to pushq %rbp, movq %rsp,%rbp.  */
+   for (i = 0; i < PROLOG_BUFSIZE; i++)
+     if (prolog_expect[i] != prolog_buf[i])
+       return pc;
+ 
+   v_function = find_pc_function (pc);
+   v_sal = find_pc_line (pc, 0);
+ 
+   /* If pc doesn't point to a function with debuginfo, 
+      some of the following may be NULL.  */
+   if (!v_function || !v_function->ginfo.value.block
+       || !v_sal.symtab)
+     return pc;
+ 
+   firstline = v_sal.line;
+   currline = firstline;
+   salendaddr = v_sal.end;
+   endaddr = v_function->ginfo.value.block->endaddr;
+ 
+   for (i = 0; i < v_sal.symtab->linetable->nitems; i++)
+     if (v_sal.symtab->linetable->item[i].line > firstline
+ 	&& v_sal.symtab->linetable->item[i].pc >= salendaddr
+ 	&& v_sal.symtab->linetable->item[i].pc < endaddr)
+       {
+ 	pc = v_sal.symtab->linetable->item[i].pc;
+ 	currline = v_sal.symtab->linetable->item[i].line;
+ 	break;
+       }
+ 
    return pc;
  }