parisc: improve ptrace support for gdb single-step

Various GCC tests use gdb to simulate a multithreaded application. Many of
these tests have been failing on parisc linux.

GCC does this by using gdb to single-step the application, then gdb is used to
call other test specific code. Where this fails is when the application is
stepped into the delay slot of a taken branch. This sets the PSW B bit. When
the test specific code is executed, this usually clears the PSW B bit.
Currently, gdb is not allowed to set the B bit. So, the code falls through what
should be a taken branch.

The attached patch adds the PSW B bit to the set of bits that gdb is allowed to
set. In order to set the B bit, the trace system call must return using an
interrupt restore. The patch also modifies this code to use the saved IAOQ
values when they are saved by a ptrace syscall or interruption.

Signed-off-by: John David Anglin <dave.anglin@bell.net>
Signed-off-by: Helge Deller <deller@gmx.de>

2 files changed, 14 insertions, 6 deletions

diff --git a/arch/parisc/kernel/entry.S b/arch/parisc/kernel/entry.S
index bfb44247d7a7..eb7850b46c25 100644
--- a/arch/parisc/kernel/entry.S
+++ b/arch/parisc/kernel/entry.S
@@ -1865,7 +1865,7 @@ syscall_restore:
 
         /* Are we being ptraced? */
         ldw     TASK_FLAGS(%r1),%r19
-        ldi     (_TIF_SINGLESTEP|_TIF_BLOCKSTEP),%r2
+        ldi     _TIF_SYSCALL_TRACE_MASK,%r2
         and,COND(=)     %r19,%r2,%r0
         b,n     syscall_restore_rfi
 
@@ -1978,15 +1978,23 @@ syscall_restore_rfi:
         /* sr2 should be set to zero for userspace syscalls */
         STREG   %r0,TASK_PT_SR2(%r1)
 
-pt_regs_ok:
         LDREG   TASK_PT_GR31(%r1),%r2
-        depi    3,31,2,%r2                         /* ensure return to user mode. */
-        STREG   %r2,TASK_PT_IAOQ0(%r1)
+        depi    3,31,2,%r2                 /* ensure return to user mode. */
+        STREG   %r2,TASK_PT_IAOQ0(%r1)
         ldo     4(%r2),%r2
         STREG   %r2,TASK_PT_IAOQ1(%r1)
+        b       intr_restore
         copy    %r25,%r16
+
+pt_regs_ok:
+        LDREG   TASK_PT_IAOQ0(%r1),%r2
+        depi    3,31,2,%r2                 /* ensure return to user mode. */
+        STREG   %r2,TASK_PT_IAOQ0(%r1)
+        LDREG   TASK_PT_IAOQ1(%r1),%r2
+        depi    3,31,2,%r2
+        STREG   %r2,TASK_PT_IAOQ1(%r1)
         b       intr_restore
-        nop
+        copy    %r25,%r16
 
         .import schedule,code
 syscall_do_resched:
diff --git a/arch/parisc/kernel/ptrace.c b/arch/parisc/kernel/ptrace.c
index 857c2f545470..534abd4936e1 100644
--- a/arch/parisc/kernel/ptrace.c
+++ b/arch/parisc/kernel/ptrace.c
@@ -26,7 +26,7 @@
 #include <asm/asm-offsets.h>
 
 /* PSW bits we allow the debugger to modify */
-#define USER_PSW_BITS   (PSW_N | PSW_V | PSW_CB)
+#define USER_PSW_BITS   (PSW_N | PSW_B | PSW_V | PSW_CB)
 
 /*
  * Called by kernel/ptrace.c when detaching..