From bab37966cfd192a12d5d1d259c7009a02cefe8b3 Mon Sep 17 00:00:00 2001 From: Simon Marchi Date: Fri, 4 Dec 2020 16:43:54 -0500 Subject: [PATCH] gdb: introduce status enum for displaced step prepare/finish This is a preparatory patch to reduce the size of the diff of the upcoming main patch. It introduces enum types for the return values of displaced step "prepare" and "finish" operations. I find that this expresses better the intention of the code, rather than returning arbitrary integer values (-1, 0 and 1) which are difficult to remember. That makes the code easier to read. I put the new enum types in a new displaced-stepping.h file, because I introduce that file in a later patch anyway. Putting it there avoids having to move it later. There is one change in behavior for displaced_step_finish: it currently returns 0 if the thread wasn't doing a displaced step and 1 if the thread was doing a displaced step which was executed successfully. It turns out that this distinction is not needed by any caller, so I've merged these two cases into "_OK", rather than adding an extra enumerator. gdb/ChangeLog: * infrun.c (displaced_step_prepare_throw): Change return type to displaced_step_prepare_status. (displaced_step_prepare): Likewise. (displaced_step_finish): Change return type to displaced_step_finish_status. (resume_1): Adjust. (stop_all_threads): Adjust. * displaced-stepping.h: New file. Change-Id: I5c8fe07212cd398d5b486b5936d9d0807acd3788 --- gdb/ChangeLog | 11 ++++++ gdb/displaced-stepping.h | 47 ++++++++++++++++++++++++++ gdb/infrun.c | 72 +++++++++++++++++++++++----------------- 3 files changed, 100 insertions(+), 30 deletions(-) create mode 100644 gdb/displaced-stepping.h diff --git a/gdb/ChangeLog b/gdb/ChangeLog index a83fa439f4f..0fe4b27c585 100644 --- a/gdb/ChangeLog +++ b/gdb/ChangeLog @@ -1,3 +1,14 @@ +2020-12-04 Simon Marchi + + * infrun.c (displaced_step_prepare_throw): Change return type to + displaced_step_prepare_status. + (displaced_step_prepare): Likewise. + (displaced_step_finish): Change return type to + displaced_step_finish_status. + (resume_1): Adjust. + (stop_all_threads): Adjust. + * displaced-stepping.h: New file. + 2020-12-04 Simon Marchi * infrun.c (displaced_step_fixup): Rename to... diff --git a/gdb/displaced-stepping.h b/gdb/displaced-stepping.h new file mode 100644 index 00000000000..44aca74111d --- /dev/null +++ b/gdb/displaced-stepping.h @@ -0,0 +1,47 @@ +/* Displaced stepping related things. + + Copyright (C) 2020 Free Software Foundation, Inc. + + This file is part of GDB. + + This program is free software; you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation; either version 3 of the License, or + (at your option) any later version. + + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU General Public License for more details. + + You should have received a copy of the GNU General Public License + along with this program. If not, see . */ + +#ifndef DISPLACED_STEPPING_H +#define DISPLACED_STEPPING_H + +enum displaced_step_prepare_status +{ + /* A displaced stepping buffer was successfully allocated and prepared. */ + DISPLACED_STEP_PREPARE_STATUS_OK, + + /* This particular instruction can't be displaced stepped, GDB should fall + back on in-line stepping. */ + DISPLACED_STEP_PREPARE_STATUS_CANT, + + /* Not enough resources are available at this time, try again later. */ + DISPLACED_STEP_PREPARE_STATUS_UNAVAILABLE, +}; + +enum displaced_step_finish_status +{ + /* Either the instruction was stepped and fixed up, or the specified thread + wasn't executing a displaced step (in which case there's nothing to + finish). */ + DISPLACED_STEP_FINISH_STATUS_OK, + + /* The thread started a displaced step, but didn't complete it. */ + DISPLACED_STEP_FINISH_STATUS_NOT_EXECUTED, +}; + +#endif /* DISPLACED_STEPPING_H */ diff --git a/gdb/infrun.c b/gdb/infrun.c index 1b747fedbbc..29bbc209d18 100644 --- a/gdb/infrun.c +++ b/gdb/infrun.c @@ -19,6 +19,7 @@ along with this program. If not, see . */ #include "defs.h" +#include "displaced-stepping.h" #include "infrun.h" #include #include "symtab.h" @@ -1650,11 +1651,13 @@ displaced_step_dump_bytes (const gdb_byte *buf, size_t len) Comments in the code for 'random signals' in handle_inferior_event explain how we handle this case instead. - Returns 1 if preparing was successful -- this thread is going to be - stepped now; 0 if displaced stepping this thread got queued; or -1 - if this instruction can't be displaced stepped. */ + Returns DISPLACED_STEP_PREPARE_STATUS_OK if preparing was successful -- this + thread is going to be stepped now; DISPLACED_STEP_PREPARE_STATUS_UNAVAILABLE + if displaced stepping this thread got queued; or + DISPLACED_STEP_PREPARE_STATUS_CANT if this instruction can't be displaced + stepped. */ -static int +static displaced_step_prepare_status displaced_step_prepare_throw (thread_info *tp) { regcache *regcache = get_thread_regcache (tp); @@ -1691,7 +1694,7 @@ displaced_step_prepare_throw (thread_info *tp) target_pid_to_str (tp->ptid).c_str ()); global_thread_step_over_chain_enqueue (tp); - return 0; + return DISPLACED_STEP_PREPARE_STATUS_UNAVAILABLE; } else displaced_debug_printf ("stepping %s now", @@ -1722,7 +1725,7 @@ displaced_step_prepare_throw (thread_info *tp) displaced_debug_printf ("breakpoint set in scratch pad. " "Stepping over breakpoint in-line instead."); - return -1; + return DISPLACED_STEP_PREPARE_STATUS_CANT; } /* Save the original contents of the copy area. */ @@ -1746,7 +1749,7 @@ displaced_step_prepare_throw (thread_info *tp) /* The architecture doesn't know how or want to displaced step this instruction or instruction sequence. Fallback to stepping over the breakpoint in-line. */ - return -1; + return DISPLACED_STEP_PREPARE_STATUS_CANT; } /* Save the information we need to fix things up if the step @@ -1767,20 +1770,21 @@ displaced_step_prepare_throw (thread_info *tp) displaced_debug_printf ("displaced pc to %s", paddress (gdbarch, copy)); - return 1; + return DISPLACED_STEP_PREPARE_STATUS_OK; } /* Wrapper for displaced_step_prepare_throw that disabled further attempts at displaced stepping if we get a memory error. */ -static int +static displaced_step_prepare_status displaced_step_prepare (thread_info *thread) { - int prepared = -1; + displaced_step_prepare_status status + = DISPLACED_STEP_PREPARE_STATUS_CANT; try { - prepared = displaced_step_prepare_throw (thread); + status = displaced_step_prepare_throw (thread); } catch (const gdb_exception_error &ex) { @@ -1803,7 +1807,7 @@ displaced_step_prepare (thread_info *thread) thread->inf->displaced_step_state.failed_before = 1; } - return prepared; + return status; } static void @@ -1833,22 +1837,24 @@ displaced_step_restore (struct displaced_step_inferior_state *displaced, displaced->step_copy)); } -/* If we displaced stepped an instruction successfully, adjust - registers and memory to yield the same effect the instruction would - have had if we had executed it at its original address, and return - 1. If the instruction didn't complete, relocate the PC and return - -1. If the thread wasn't displaced stepping, return 0. */ +/* If we displaced stepped an instruction successfully, adjust registers and + memory to yield the same effect the instruction would have had if we had + executed it at its original address, and return + DISPLACED_STEP_FINISH_STATUS_OK. If the instruction didn't complete, + relocate the PC and return DISPLACED_STEP_FINISH_STATUS_NOT_EXECUTED. -static int + If the thread wasn't displaced stepping, return + DISPLACED_STEP_FINISH_STATUS_OK as well. */ + +static displaced_step_finish_status displaced_step_finish (thread_info *event_thread, enum gdb_signal signal) { displaced_step_inferior_state *displaced = &event_thread->inf->displaced_step_state; - int ret; /* Was this event for the thread we displaced? */ if (displaced->step_thread != event_thread) - return 0; + return DISPLACED_STEP_FINISH_STATUS_OK; /* Fixup may need to read memory/registers. Switch to the thread that we're fixing up. Also, target_stopped_by_watchpoint checks @@ -1872,7 +1878,8 @@ displaced_step_finish (thread_info *event_thread, enum gdb_signal signal) displaced->step_original, displaced->step_copy, get_thread_regcache (displaced->step_thread)); - ret = 1; + + return DISPLACED_STEP_FINISH_STATUS_OK; } else { @@ -1883,10 +1890,9 @@ displaced_step_finish (thread_info *event_thread, enum gdb_signal signal) pc = displaced->step_original + (pc - displaced->step_copy); regcache_write_pc (regcache, pc); - ret = -1; - } - return ret; + return DISPLACED_STEP_FINISH_STATUS_NOT_EXECUTED; + } } /* Data to be passed around while handling an event. This data is @@ -2410,16 +2416,17 @@ resume_1 (enum gdb_signal sig) && sig == GDB_SIGNAL_0 && !current_inferior ()->waiting_for_vfork_done) { - int prepared = displaced_step_prepare (tp); + displaced_step_prepare_status prepare_status + = displaced_step_prepare (tp); - if (prepared == 0) + if (prepare_status == DISPLACED_STEP_PREPARE_STATUS_UNAVAILABLE) { infrun_debug_printf ("Got placed in step-over queue"); tp->control.trap_expected = 0; return; } - else if (prepared < 0) + else if (prepare_status == DISPLACED_STEP_PREPARE_STATUS_CANT) { /* Fallback to stepping over the breakpoint in-line. */ @@ -2433,7 +2440,7 @@ resume_1 (enum gdb_signal sig) insert_breakpoints (); } - else if (prepared > 0) + else if (prepare_status == DISPLACED_STEP_PREPARE_STATUS_OK) { /* Update pc to reflect the new address from which we will execute instructions due to displaced stepping. */ @@ -2441,6 +2448,9 @@ resume_1 (enum gdb_signal sig) step = gdbarch_displaced_step_hw_singlestep (gdbarch); } + else + gdb_assert_not_reached (_("Invalid displaced_step_prepare_status " + "value.")); } /* Do we need to do it the hard way, w/temp breakpoints? */ @@ -4815,7 +4825,8 @@ stop_all_threads (void) t->suspend.waitstatus.kind = TARGET_WAITKIND_IGNORE; t->suspend.waitstatus_pending_p = 0; - if (displaced_step_finish (t, GDB_SIGNAL_0) < 0) + if (displaced_step_finish (t, GDB_SIGNAL_0) + == DISPLACED_STEP_FINISH_STATUS_NOT_EXECUTED) { /* Add it back to the step-over queue. */ infrun_debug_printf @@ -4843,7 +4854,8 @@ stop_all_threads (void) sig = (event.ws.kind == TARGET_WAITKIND_STOPPED ? event.ws.value.sig : GDB_SIGNAL_0); - if (displaced_step_finish (t, sig) < 0) + if (displaced_step_finish (t, sig) + == DISPLACED_STEP_FINISH_STATUS_NOT_EXECUTED) { /* Add it back to the step-over queue. */ t->control.trap_expected = 0; -- 2.30.2