gdbserver: 64-bit kernel / 32-inferior, syscall restarting

$ make check RUNTESTFLAGS="--target_board=native-gdbserver/-m32 clone-thread_db.exp"

gdb.log shows:

  Running target native-gdbserver/-m32
  ...
  clone-thread_db: src/gdb/testsuite/gdb.threads/clone-thread_db.c:57: thread_fn: Assertion `res != -1' failed.
  ...
  (gdb) FAIL: gdb.threads/clone-thread_db.exp: continue to end

That was waitpid returning -1 / EINTR.  We don't see that when testing
with unix/-m32 (native debugging).  Turns out to be that when
debugging a 32-bit inferior, a 64-bit GDBserver is reading/writing
$orig_eax from/to the wrong ptrace register buffer offset.  When
gdbserver is 64-bit, the ptrace register buffer is in 64-bit layout,
so the register is found at "ORIG_EAX * 8", not at "ORIG_EAX * 4".

Fixes these with --target_board=native-gdbserver/-m32 on x86_64 Fedora 20:

    -FAIL: gdb.threads/clone-thread_db.exp: continue to end
    +PASS: gdb.threads/clone-thread_db.exp: continue to end

    -FAIL: gdb.threads/hand-call-in-threads.exp: all dummies popped
    +PASS: gdb.threads/hand-call-in-threads.exp: all dummies popped
     PASS: gdb.threads/hand-call-in-threads.exp: breakpoint on all_threads_running
     PASS: gdb.threads/hand-call-in-threads.exp: breakpoint on hand_call
     PASS: gdb.threads/hand-call-in-threads.exp: disable scheduler locking
    @@ -29339,15 +29331,15 @@ PASS: gdb.threads/hand-call-in-threads.e
     PASS: gdb.threads/hand-call-in-threads.exp: discard hand call, thread 4
     PASS: gdb.threads/hand-call-in-threads.exp: discard hand call, thread 5
     PASS: gdb.threads/hand-call-in-threads.exp: dummy stack frame number, thread 1
    -FAIL: gdb.threads/hand-call-in-threads.exp: dummy stack frame number, thread 2
    -FAIL: gdb.threads/hand-call-in-threads.exp: dummy stack frame number, thread 3
    -FAIL: gdb.threads/hand-call-in-threads.exp: dummy stack frame number, thread 4
    +PASS: gdb.threads/hand-call-in-threads.exp: dummy stack frame number, thread 2
    +PASS: gdb.threads/hand-call-in-threads.exp: dummy stack frame number, thread 3
    +PASS: gdb.threads/hand-call-in-threads.exp: dummy stack frame number, thread 4
     PASS: gdb.threads/hand-call-in-threads.exp: dummy stack frame number, thread 5
     PASS: gdb.threads/hand-call-in-threads.exp: enable scheduler locking
     PASS: gdb.threads/hand-call-in-threads.exp: hand call, thread 1
    -FAIL: gdb.threads/hand-call-in-threads.exp: hand call, thread 2
    -FAIL: gdb.threads/hand-call-in-threads.exp: hand call, thread 3
    -FAIL: gdb.threads/hand-call-in-threads.exp: hand call, thread 4
    +PASS: gdb.threads/hand-call-in-threads.exp: hand call, thread 2
    +PASS: gdb.threads/hand-call-in-threads.exp: hand call, thread 3
    +PASS: gdb.threads/hand-call-in-threads.exp: hand call, thread 4
     PASS: gdb.threads/hand-call-in-threads.exp: hand call, thread 5
     PASS: gdb.threads/hand-call-in-threads.exp: prepare to discard hand call, thread 1
     PASS: gdb.threads/hand-call-in-threads.exp: prepare to discard hand call, thread 2

gdb/gdbserver/ChangeLog
2015-02-23  Pedro Alves  <palves@redhat.com>

	* linux-x86-low.c (REGSIZE): Define in both 32-bit and 64-bit
	modes.
	(x86_fill_gregset, x86_store_gregset): Use it when handling
	$orig_eax.

2 files changed, 12 insertions, 2 deletions

diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog
index cfdb3e7..d724e6c 100644
--- a/gdb/gdbserver/ChangeLog
+++ b/gdb/gdbserver/ChangeLog
@@ -1,3 +1,10 @@
+2015-02-23  Pedro Alves  <palves@redhat.com>
+
+	* linux-x86-low.c (REGSIZE): Define in both 32-bit and 64-bit
+	modes.
+	(x86_fill_gregset, x86_store_gregset): Use it when handling
+	$orig_eax.
+
 2015-02-20  Pedro Alves  <palves@redhat.com>
 
 	* thread-db.c: Include "nat/linux-procfs.h".
diff --git a/gdb/gdbserver/linux-x86-low.c b/gdb/gdbserver/linux-x86-low.c
index 2c3fccc..e58a7ac 100644
--- a/gdb/gdbserver/linux-x86-low.c
+++ b/gdb/gdbserver/linux-x86-low.c
@@ -176,6 +176,7 @@ static /*const*/ int i386_regmap[] =
 
 /* So code below doesn't have to care, i386 or amd64.  */
 #define ORIG_EAX ORIG_RAX
+#define REGSIZE 8
 
 static const int x86_64_regmap[] =
 {
@@ -221,6 +222,8 @@ static /*const*/ int i386_regmap[] =
 
 #define I386_NUM_REGS (sizeof (i386_regmap) / sizeof (i386_regmap[0]))
 
+#define REGSIZE 4
+
 #endif
 
 #ifdef __x86_64__
@@ -374,7 +377,7 @@ x86_fill_gregset (struct regcache *regcache, void *buf)
     collect_register (regcache, i, ((char *) buf) + i386_regmap[i]);
 
   collect_register_by_name (regcache, "orig_eax",
-			    ((char *) buf) + ORIG_EAX * 4);
+			    ((char *) buf) + ORIG_EAX * REGSIZE);
 }
 
 static void
@@ -396,7 +399,7 @@ x86_store_gregset (struct regcache *regcache, const void *buf)
     supply_register (regcache, i, ((char *) buf) + i386_regmap[i]);
 
   supply_register_by_name (regcache, "orig_eax",
-			   ((char *) buf) + ORIG_EAX * 4);
+			   ((char *) buf) + ORIG_EAX * REGSIZE);
 }
 
 static void