Re: Teach gdbserver to step over internal breakpoints

[Pedro Alves <pedro at codesourcery dot com>]

On Wednesday 24 March 2010 21:22:39, Pedro Alves wrote:
> Also tested on x86_64, with and without a thread
> event breakpoint, and also with a had that makes x86-64
> use reinsert breakpoints.  I'll show that for the archives
> shortly.

s/a had/ a hack/.  Here it is.  This makes an x86 gdbserver
use reinsert (single software single-step) breakpoints to
step over the thread event breakpoint, thus it make it
easier to test those code paths on my devel machine.

I've only used it thoroughly with x86-64, but it should
work with ix86 as well.

For the archives.

-- 
Pedro Alves
---
 gdb/gdbserver/linux-low.c     |    2 +-
 gdb/gdbserver/linux-x86-low.c |   35 ++++++++++++++++++++++++++++++++++-
 2 files changed, 35 insertions(+), 2 deletions(-)

Index: src/gdb/gdbserver/linux-x86-low.c
===================================================================
--- src.orig/gdb/gdbserver/linux-x86-low.c	2010-03-24 20:34:18.000000000 +0000
+++ src/gdb/gdbserver/linux-x86-low.c	2010-03-24 21:41:42.000000000 +0000
@@ -824,6 +824,39 @@ x86_arch_setup (void)
   num_xmm_registers = 8;
 }
 
+/* We only place breakpoints in empty marker functions, and thread
+   locking is outside of the function.  So rather than importing
+   software single-step, we can just run until exit.  */
+
+static CORE_ADDR
+x86_reinsert_addr (void)
+{
+  struct regcache *regcache = get_thread_regcache (current_inferior, 1);
+
+#ifdef __x86_64__
+  int use_64bit = register_size (0) == 8;
+
+  if (use_64bit)
+    {
+      unsigned long sp, ret;
+
+      collect_register_by_name (regcache, "rsp", &sp);
+      if (read_inferior_memory (sp, (unsigned char *) &ret, 8) != 0)
+	return 0;
+      return ret;
+    }
+  else
+#endif
+    {
+      unsigned int sp, ret;
+
+      collect_register_by_name (regcache, "esp", &sp);
+      if (read_inferior_memory (sp, (unsigned char *) &ret, 4) != 0)
+	return 0;
+      return ret;
+    }
+}
+
 /* This is initialized assuming an amd64 target.
    x86_arch_setup will correct it for i386 or amd64 targets.  */
 
@@ -838,7 +871,7 @@ struct linux_target_ops the_low_target =
   x86_set_pc,
   x86_breakpoint,
   x86_breakpoint_len,
-  NULL,
+  x86_reinsert_addr,
   1,
   x86_breakpoint_at,
   x86_insert_point,
Index: src/gdb/gdbserver/linux-low.c
===================================================================
--- src.orig/gdb/gdbserver/linux-low.c	2010-03-24 21:43:01.000000000 +0000
+++ src/gdb/gdbserver/linux-low.c	2010-03-24 21:55:16.000000000 +0000
@@ -3421,7 +3421,7 @@ linux_look_up_symbols (void)
   /* If the kernel supports tracing forks then it also supports tracing
      clones, and then we don't need to use the magic thread event breakpoint
      to learn about threads.  */
-  thread_db_init (!linux_supports_tracefork_flag);
+  thread_db_init (1);
 #endif
 }