[PATCH master/7.12] Throw error when ptrace fail in regsets_fetch_inferior_registers

[Yao Qi <qiyaoltc@gmail.com>]

When I run process-dies-while-detaching.exp with GDBserver, I see many
warnings printed by GDBserver,

ptrace(regsets_fetch_inferior_registers) PID=26183: No such process
ptrace(regsets_fetch_inferior_registers) PID=26183: No such process
ptrace(regsets_fetch_inferior_registers) PID=26184: No such process
ptrace(regsets_fetch_inferior_registers) PID=26184: No such process

regsets_fetch_inferior_registers is called when GDBserver resumes each
lwp.

 #2  0x0000000000428260 in regsets_fetch_inferior_registers (regsets_info=0x4690d0 <aarch64_regsets_info>, regcache=0x31832020)
    at /home/yao/SourceCode/gnu/gdb/git/gdb/gdbserver/linux-low.c:5412
 #3  0x00000000004070e8 in get_thread_regcache (thread=0x31832940, fetch=fetch@entry=1) at /home/yao/SourceCode/gnu/gdb/git/gdb/gdbserver/regcache.c:58
 #4  0x0000000000429c40 in linux_resume_one_lwp_throw (info=<optimized out>, signal=0, step=0, lwp=0x31832830)
    at /home/yao/SourceCode/gnu/gdb/git/gdb/gdbserver/linux-low.c:4463
 #5  linux_resume_one_lwp (lwp=0x31832830, step=<optimized out>, signal=<optimized out>, info=<optimized out>)
    at /home/yao/SourceCode/gnu/gdb/git/gdb/gdbserver/linux-low.c:4573

The is the case that threads are disappeared when GDB/GDBserver resumes
them.  Our fix nowadays is to throw exception, caller
linux_resume_one_lwp catches the exception, and swallow it if the lwp
is gone.  See linux-low.c:linux_resume_one_lwp.  So this patch fixes
the problem by throwing exception in regsets_fetch_inferior_registers.
Another caller of regsets_fetch_inferior_registers, linux_fetch_registers,
needs to catch the exception the same way as linux_resume_one_lwp does.

gdb/gdbserver:

2016-08-02  Yao Qi  <yao.qi@linaro.org>

	* linux-low.c (regsets_fetch_inferior_registers): Throw
	exception on ptrace fail.
	(linux_fetch_registers): Rename to ...
	(linux_fetch_registers_throw): ... it.
	(linux_fetch_registers): Call linux_fetch_registers_throw
	and catch the exception.  If check_ptrace_stopped_lwp_gone
	is false, throw it again.
---
 gdb/gdbserver/linux-low.c | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
index e251ac4..c72b78c 100644
--- a/gdb/gdbserver/linux-low.c
+++ b/gdb/gdbserver/linux-low.c
@@ -5410,7 +5410,7 @@ regsets_fetch_inferior_registers (struct regsets_info *regsets_info,
 	      char s[256];
 	      sprintf (s, "ptrace(regsets_fetch_inferior_registers) PID=%d",
 		       pid);
-	      perror (s);
+	      perror_with_name (_(s));
 	    }
 	}
       else
@@ -5702,7 +5702,7 @@ usr_store_inferior_registers (const struct regs_info *regs_info,
 
 
 static void
-linux_fetch_registers (struct regcache *regcache, int regno)
+linux_fetch_registers_throw (struct regcache *regcache, int regno)
 {
   int use_regsets;
   int all = 0;
@@ -5735,6 +5735,23 @@ linux_fetch_registers (struct regcache *regcache, int regno)
 }
 
 static void
+linux_fetch_registers (struct regcache *regcache, int regno)
+{
+  TRY
+    {
+      linux_fetch_registers_throw (regcache, regno);
+    }
+  CATCH (ex, RETURN_MASK_ERROR)
+    {
+      struct lwp_info *lwp = get_thread_lwp (current_thread);
+
+      if (!check_ptrace_stopped_lwp_gone (lwp))
+	throw_exception (ex);
+    }
+  END_CATCH
+}
+
+static void
 linux_store_registers (struct regcache *regcache, int regno)
 {
   int use_regsets;
-- 
1.9.1