Re: [RFC][patch] Allow to disassemble line.

Paul Pluzhnikov
2009-10-16T23:07:20Z

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On Thu, Oct 8, 2009 at 9:52 AM, Paul Pluzhnikov <ppluzhnikov@google.com> wrote:

> On Thu, Oct 8, 2009 at 9:23 AM, Daniel Jacobowitz <drow@false.org> wrote:
>
>> I'd mildly prefer changing the behavior of GDB - but only if we can
>> get an additional enhancement that I don't think we have yet: "*" at
>> the PC...
>
> That sounds good. I'll try to implement that.

Here my attempt to implement that.

I am guessing that it is flawed, as it possibly breaks something in MI
(which I don't understand yet).

It also breaks quite a few test cases -- I'll adjust expected patterns if
it is decided to go ahead with this.

I should say that from CLI perspective I like this very much. On x86,
often you need to examine 10 or so instructions before the crash point.

I usually do 'x/10i $pc-15' (as instruction size is not fixed), and then
"hunt" for the current PC in the resulting output. This patch makes it so
much easier:

(top) x/10i $pc-15
0x54d212 <catch_errors+54>: mov -0x10(%rbp),%edi
0x54d215 <catch_errors+57>: mov $0x1,%esi
0x54d21a <catch_errors+62>: callq 0x452c38 <__sigsetjmp@plt>
0x54d21f <catch_errors+67>: jmp 0x54d237 <catch_errors+91>
* 0x54d221 <catch_errors+69>: mov -0x30(%rbp),%rdi
0x54d225 <catch_errors+73>: mov -0x28(%rbp),%rax
0x54d229 <catch_errors+77>: callq *%rax
0x54d22b <catch_errors+79>: mov %eax,-0x4(%rbp)
0x54d22e <catch_errors+82>: callq 0x54c9c0
<exceptions_state_mc_action_iter_1>
0x54d233 <catch_errors+87>: test %eax,%eax

I also like how 'disassemble-next-line on' works:

(top) set disassemble-next-line on
(top) ni
0x000000000054d225 510 val = func (func_args);
0x000000000054d221 <catch_errors+69>: 48 8b 7d d0 mov -0x30(%rbp),%rdi
* 0x000000000054d225 <catch_errors+73>: 48 8b 45 d8 mov -0x28(%rbp),%rax
0x000000000054d229 <catch_errors+77>: ff d0 callq *%rax
0x000000000054d22b <catch_errors+79>: 89 45 fc mov %eax,-0x4(%rbp)
(top) ni
0x000000000054d229 510 val = func (func_args);
0x000000000054d221 <catch_errors+69>: 48 8b 7d d0 mov -0x30(%rbp),%rdi
0x000000000054d225 <catch_errors+73>: 48 8b 45 d8 mov -0x28(%rbp),%rax
* 0x000000000054d229 <catch_errors+77>: ff d0 callq *%rax
0x000000000054d22b <catch_errors+79>: 89 45 fc mov %eax,-0x4(%rbp)

As well as how 'disas' works:

(top) disas
Dump of assembler code for function catch_errors:
0x000000000054d1dc <catch_errors+0>: push %rbp
0x000000000054d1dd <catch_errors+1>: mov %rsp,%rbp
0x000000000054d1e0 <catch_errors+4>: sub $0x40,%rsp
0x000000000054d1e4 <catch_errors+8>: mov %rdi,-0x28(%rbp)
0x000000000054d1e8 <catch_errors+12>: mov %rsi,-0x30(%rbp)
0x000000000054d1ec <catch_errors+16>: mov %rdx,-0x38(%rbp)
0x000000000054d1f0 <catch_errors+20>: mov %ecx,-0x3c(%rbp)
0x000000000054d1f3 <catch_errors+23>: movl $0x0,-0x4(%rbp)
0x000000000054d1fa <catch_errors+30>: mov 0x56e1bf(%rip),%rdi
# 0xabb3c0 <uiout>
0x000000000054d201 <catch_errors+37>: mov -0x3c(%rbp),%edx
0x000000000054d204 <catch_errors+40>: lea -0x20(%rbp),%rsi
0x000000000054d208 <catch_errors+44>: callq 0x54c678
<exceptions_state_mc_init>
0x000000000054d20d <catch_errors+49>: mov %rax,-0x10(%rbp)
0x000000000054d211 <catch_errors+53>: mov -0x10(%rbp),%rdi
0x000000000054d215 <catch_errors+57>: mov $0x1,%esi
0x000000000054d21a <catch_errors+62>: callq 0x452c38 <__sigsetjmp@plt>
0x000000000054d21f <catch_errors+67>: jmp 0x54d237 <catch_errors+91>
0x000000000054d221 <catch_errors+69>: mov -0x30(%rbp),%rdi
0x000000000054d225 <catch_errors+73>: mov -0x28(%rbp),%rax
* 0x000000000054d229 <catch_errors+77>: callq *%rax
0x000000000054d22b <catch_errors+79>: mov %eax,-0x4(%rbp)
0x000000000054d22e <catch_errors+82>: callq 0x54c9c0
<exceptions_state_mc_action_iter_1>
0x000000000054d233 <catch_errors+87>: test %eax,%eax
0x000000000054d235 <catch_errors+89>: jne 0x54d221 <catch_errors+69>
0x000000000054d237 <catch_errors+91>: callq 0x54c9b0
<exceptions_state_mc_action_iter>
0x000000000054d23c <catch_errors+96>: test %eax,%eax
0x000000000054d23e <catch_errors+98>: jne 0x54d22e <catch_errors+82>
0x000000000054d240 <catch_errors+100>: mov
0x593721(%rip),%rdi # 0xae0968 <gdb_stderr>
0x000000000054d247 <catch_errors+107>: mov -0x20(%rbp),%rdx
0x000000000054d24b <catch_errors+111>: mov -0x18(%rbp),%rcx
0x000000000054d24f <catch_errors+115>: mov -0x38(%rbp),%rsi
0x000000000054d253 <catch_errors+119>: callq 0x54cdea
<print_any_exception>
0x000000000054d258 <catch_errors+124>: mov -0x20(%rbp),%eax
0x000000000054d25b <catch_errors+127>: test %eax,%eax
0x000000000054d25d <catch_errors+129>: je 0x54d268
<catch_errors+140>
0x000000000054d25f <catch_errors+131>: movl $0x0,-0x40(%rbp)
0x000000000054d266 <catch_errors+138>: jmp 0x54d26e
<catch_errors+146>
0x000000000054d268 <catch_errors+140>: mov -0x4(%rbp),%eax
0x000000000054d26b <catch_errors+143>: mov %eax,-0x40(%rbp)
0x000000000054d26e <catch_errors+146>: mov -0x40(%rbp),%eax
0x000000000054d271 <catch_errors+149>: leaveq
0x000000000054d272 <catch_errors+150>: retq
End of assembler dump.

Thanks,
--
Paul Pluzhnikov

2009-10-16 Paul Pluzhnikov <ppluzhnikov@google.com>

* defs.h (pc_prefix): New prototype.
* disasm.c (dump_insns): Identify instruction address as such.
* ui-out.c (ui_out_field_core_addr): Highlight current instruction.
* printcmd.c (do_examine): Likewise.
(pc_prefix, print_pc_prefix): New function.
* stack.c (print_frame_info): Disassemble entire current line.

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Index: defs.h
===================================================================
RCS file: /cvs/src/src/gdb/defs.h,v
retrieving revision 1.255
diff -u -p -u -r1.255 defs.h
--- defs.h 22 Sep 2009 22:34:17 -0000 1.255
+++ defs.h 16 Oct 2009 22:37:36 -0000
@@ -608,6 +608,7 @@ extern int build_address_symbolic (CORE_
int *unmapped);

extern void print_address (struct gdbarch *, CORE_ADDR, struct ui_file *);
+extern const char *pc_prefix (CORE_ADDR);

/* From source.c */

Index: disasm.c
===================================================================
RCS file: /cvs/src/src/gdb/disasm.c,v
retrieving revision 1.33
diff -u -p -u -r1.33 disasm.c
--- disasm.c 11 Jul 2009 14:04:23 -0000 1.33
+++ disasm.c 16 Oct 2009 22:37:36 -0000
@@ -113,7 +113,7 @@ dump_insns (struct gdbarch *gdbarch, str
num_displayed++;
}
ui_out_chain = make_cleanup_ui_out_tuple_begin_end (uiout, NULL);
- ui_out_field_core_addr (uiout, "address", gdbarch, pc);
+ ui_out_field_core_addr (uiout, "pc_addr", gdbarch, pc);

if (!build_address_symbolic (pc, 0, &name, &offset, &filename,
&line, &unmapped))
Index: printcmd.c
===================================================================
RCS file: /cvs/src/src/gdb/printcmd.c,v
retrieving revision 1.164
diff -u -p -u -r1.164 printcmd.c
--- printcmd.c 2 Jul 2009 17:25:58 -0000 1.164
+++ printcmd.c 16 Oct 2009 22:37:36 -0000
@@ -716,6 +716,32 @@ print_address (struct gdbarch *gdbarch,
print_address_symbolic (addr, stream, asm_demangle, " ");
}

+/* Return a prefix for instruction address:
+ "* " for current instruction, else " ". */
+
+const char *
+pc_prefix (CORE_ADDR addr)
+{
+ if (has_stack_frames ())
+ {
+ struct frame_info *frame;
+ CORE_ADDR pc;
+
+ frame = get_selected_frame (NULL);
+ pc = get_frame_pc (frame);
+
+ if (pc == addr)
+ return "* ";
+ }
+ return " ";
+}
+
+static void
+print_pc_prefix (CORE_ADDR addr, struct ui_file *stream)
+{
+ fputs_filtered (pc_prefix (addr), stream);
+}
+
/* Print address ADDR symbolically on STREAM. Parameter DEMANGLE
controls whether to print the symbolic name "raw" or demangled.
Global setting "addressprint" controls whether to print hex address
@@ -808,6 +834,8 @@ do_examine (struct format_data fmt, stru
while (count > 0)
{
QUIT;
+ if (format == 'i')
+ print_pc_prefix (next_address, gdb_stdout);
print_address (next_gdbarch, next_address, gdb_stdout);
printf_filtered (":");
for (i = maxelts;
Index: ui-out.c
===================================================================
RCS file: /cvs/src/src/gdb/ui-out.c,v
retrieving revision 1.43
diff -u -p -u -r1.43 ui-out.c
--- ui-out.c 2 Jul 2009 17:21:07 -0000 1.43
+++ ui-out.c 16 Oct 2009 22:37:36 -0000
@@ -505,6 +505,9 @@ ui_out_field_core_addr (struct ui_out *u
else
strcpy (addstr, hex_string_custom (address, 16));

+ if (strcmp (fldname, "pc_addr") == 0)
+ ui_out_text (uiout, pc_prefix (address));
+
ui_out_field_string (uiout, fldname, addstr);
}