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[RFA] skip_prologue_sal and sal expansion
- From: Jerome Guitton <guitton at adacore dot com>
- To: gdb-patches at sourceware dot org
- Date: Tue, 2 Jun 2009 18:21:33 +0200
- Subject: [RFA] skip_prologue_sal and sal expansion
A couple of cleanups in breakpoint.c. Let me give some background
first; consider the following program:
int counter = 42;
inline void
callee ()
{
counter = 0; /* set breakpoint in an inlined function. */
}
void
caller ()
{
callee ();
}
int
main ()
{
caller ();
callee ();
return counter;
}
When callee is inlined, we have three occurence for the line
"counter = 0;": inlined in caller, inlined in main, and not inlined.
When a breakpoint is set on this line, GDB sets a breakpoint on 3
locations.
(gdb) l p.c:6
1 int counter = 42;
2
3 inline void
4 callee ()
5 {
6 counter = 0;
7 }
8
9 void
10 caller ()
(gdb) b 6
Breakpoint 1 at 0x1800074: file p.c, line 6. (3 locations)
I have recently hit a bug in an assembler which was optimizing out the
prologue line info; it was making GDB think that the line
"counter = 0;" was a part of callee's prologue. And this pointed me to
something strange in GDB.
After having used this bogus assembler to generate my program, if I try
to set a breakpoint at line "counter = 0;", I end up with only one
occurence instead of three:
(gdb) b 6
Breakpoint 1 at 0x1800074: file p.c, line 6.
The problem was in skip_prologue_sal defined in breakpoint.c. When it
actually skips a prologue, it does not assure that the other sal's
fields (explicit_pc and explicit_line) are left unchanged. In my case,
it was accidently changing explicit_line from 1 to 0. This change
disabled the line sal expansion, and in consequence we ended up with
the breakpoint set in only one location. I think that it's a bug in
skip_prologue_sal, this function should not change mess with these
fields.
Now, if I change skip_prologue_sal to copy explicit_line and
explicit_pc, the line expansion is done; but we should make sure that
prologue is skipped similarly, otherwise we get an assertion failure
when the address returned by resolve_sal_pc cannot be found after
line sal expansion:
(gdb) break p.c:6
../../src/gdb/breakpoint.c:5113: internal-error: expand_line_sal_maybe:
Assertion `found' failed.
Patch attached, tested on x86-linux. OK to apply?
2009-06-02 Jerome Guitton <guitton@adacore.com>
* breakpoint.c (expand_line_sal_maybe): When explicit_line,
skip prologue on each sals.
(skip_prologue_sal): Return explicit_line and explicit_pc
unmodified.
Index: breakpoint.c
===================================================================
--- breakpoint.c (revision 148760)
+++ breakpoint.c (working copy)
@@ -207,6 +207,9 @@ static void disable_trace_command (char
static void trace_pass_command (char *, int);
+static void skip_prologue_sal (struct symtab_and_line *sal);
+
+
/* Flag indicating that a command has proceeded the inferior past the
current breakpoint. */
@@ -5412,6 +5415,15 @@ expand_line_sal_maybe (struct symtab_and
}
}
}
+ else
+ {
+ for (i = 0; i < expanded.nelts; ++i)
+ {
+ /* If this SAL corresponds to a breakpoint inserted using a
+ line number, then skip the function prologue if necessary. */
+ skip_prologue_sal (&expanded.sals[i]);
+ }
+ }
if (expanded.nelts <= 1)
@@ -5896,7 +5908,8 @@ set_breakpoint (char *address, char *con
/* Adjust SAL to the first instruction past the function prologue.
The end of the prologue is determined using the line table from
- the debugging information.
+ the debugging information. explicit_pc and explicit_line are
+ not modified.
If SAL is already past the prologue, then do nothing. */
@@ -5911,7 +5924,11 @@ skip_prologue_sal (struct symtab_and_lin
start_sal = find_function_start_sal (sym, 1);
if (sal->pc < start_sal.pc)
- *sal = start_sal;
+ {
+ start_sal.explicit_line = sal->explicit_line;
+ start_sal.explicit_pc = sal->explicit_pc;
+ *sal = start_sal;
+ }
}
/* Helper function for break_command_1 and disassemble_command. */