From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 7505 invoked by alias); 16 Jul 2012 06:34:10 -0000 Received: (qmail 7162 invoked by uid 22791); 16 Jul 2012 06:34:06 -0000 X-SWARE-Spam-Status: No, hits=-3.8 required=5.0 tests=AWL,BAYES_00,KHOP_RCVD_UNTRUST,KHOP_THREADED,RCVD_IN_HOSTKARMA_W,RCVD_IN_HOSTKARMA_WL,SPF_NEUTRAL X-Spam-Check-By: sourceware.org Received: from ozlabs.org (HELO ozlabs.org) (203.10.76.45) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Mon, 16 Jul 2012 06:33:53 +0000 Received: from kryten (ppp121-44-6-198.lns20.syd6.internode.on.net [121.44.6.198]) (using TLSv1.2 with cipher DHE-RSA-AES128-SHA (128/128 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPSA id C4F442C00F6; Mon, 16 Jul 2012 16:33:51 +1000 (EST) Date: Mon, 16 Jul 2012 06:34:00 -0000 From: Anton Blanchard To: Joel Brobecker Cc: gdb-patches@sourceware.org Subject: Re: [PATCH 2/3] Support up to 3 conditional branches in an atomic sequence Message-ID: <20120716163355.74acba34@kryten> In-Reply-To: <20120613160208.GH18729@adacore.com> References: <20120606135557.7da37cbe@kryten> <20120606135655.57bd5b54@kryten> <20120613160208.GH18729@adacore.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org X-SW-Source: 2012-07/txt/msg00205.txt.bz2 Hi Joel, Thanks for the review. > Mostly OK. I would like you to change the name of the macro to > MAX_SINGLE_STEP_BREAKPOINTS, though. Can you, please? Makes sense, done. > > + if (last_breakpoint >= (NR_SINGLE_STEP_BREAKPOINTS-1)) > > + return 0; /* too many conditional branches found, > > fallback > > Can you remove the extra parens which are useless in this case? > And binary operators should have a space before and after. Done. > > Index: gdb/gdb/breakpoint.h > [...] > > -/* Manage a software single step breakpoint (or two). Insert may > > be > > - called twice before remove is called. */ > > +/* Manage software single step breakpoints. */ > > +#define NR_SINGLE_STEP_BREAKPOINTS 4 > > + > > Just curious: Why did you remove the second sentence from the comment? > Is it no longer true? Maybe it is the "twice" that should be changed > into "multiple times"? Agreed. Here is a new version. Anton -- gdb currently supports 1 conditional branch inside a ppc larx/stcx critical region. Unfortunately there is existing code that contains more than 1, for example in the ppc64 Linux kernel: c00000000003ac18 <.__hash_page_4K>: ... c00000000003ac4c: 7f e0 30 a8 ldarx r31,0,r6 c00000000003ac50: 7c 80 f8 79 andc. r0,r4,r31 c00000000003ac54: 40 82 02 94 bne- c00000000003aee8 c00000000003ac58: 73 e0 08 00 andi. r0,r31,2048 c00000000003ac5c: 40 82 01 b0 bne- c00000000003ae0c c00000000003ac60: 54 9e f6 30 rlwinm r30,r4,30,24,24 c00000000003ac64: 7f de fb 78 or r30,r30,r31 c00000000003ac68: 63 de 09 00 ori r30,r30,2304 c00000000003ac6c: 67 de 10 00 oris r30,r30,4096 c00000000003ac70: 7f c0 31 ad stdcx. r30,0,r6 If we try to single step through this we get stuck forever because the reservation is never set when we step over the stdcx. The following patch bumps the number to 3 conditional branches + 1 terminating branch. With this patch applied I can single step through the offending function in the ppc64 Linux kernel. 2012-06-05 Anton Blanchard * gdb/breakpoint.h: Define MAX_SINGLE_STEP_BREAKPOINTS * rs6000-tdep.c (ppc_deal_with_atomic_sequence): Allow for more than two breakpoints. * gdb/breakpoint.c (insert_single_step_breakpoint): Likewise (insert_single_step_breakpoint): Likewise (single_step_breakpoints_inserted): Likewise (cancel_single_step_breakpoints): Likewise (detach_single_step_breakpoints): Likewise (single_step_breakpoint_inserted_here_p): Likewise Index: b/gdb/rs6000-tdep.c =================================================================== --- a/gdb/rs6000-tdep.c +++ b/gdb/rs6000-tdep.c @@ -1087,7 +1087,7 @@ ppc_deal_with_atomic_sequence (struct fr struct address_space *aspace = get_frame_address_space (frame); enum bfd_endian byte_order = gdbarch_byte_order (gdbarch); CORE_ADDR pc = get_frame_pc (frame); - CORE_ADDR breaks[2] = {-1, -1}; + CORE_ADDR breaks[MAX_SINGLE_STEP_BREAKPOINTS]; CORE_ADDR loc = pc; CORE_ADDR closing_insn; /* Instruction that closes the atomic sequence. */ int insn = read_memory_integer (loc, PPC_INSN_SIZE, byte_order); @@ -1096,7 +1096,6 @@ ppc_deal_with_atomic_sequence (struct fr int last_breakpoint = 0; /* Defaults to 0 (no breakpoints placed). */ const int atomic_sequence_length = 16; /* Instruction sequence length. */ int opcode; /* Branch instruction's OPcode. */ - int bc_insn_count = 0; /* Conditional branch instruction count. */ /* Assume all atomic sequences start with a lwarx/ldarx instruction. */ if ((insn & LWARX_MASK) != LWARX_INSTRUCTION @@ -1110,24 +1109,20 @@ ppc_deal_with_atomic_sequence (struct fr loc += PPC_INSN_SIZE; insn = read_memory_integer (loc, PPC_INSN_SIZE, byte_order); - /* Assume that there is at most one conditional branch in the atomic - sequence. If a conditional branch is found, put a breakpoint in - its destination address. */ if ((insn & BRANCH_MASK) == BC_INSN) { int immediate = ((insn & 0xfffc) ^ 0x8000) - 0x8000; int absolute = insn & 2; - if (bc_insn_count >= 1) - return 0; /* More than one conditional branch found, fallback + if (last_breakpoint >= MAX_SINGLE_STEP_BREAKPOINTS - 1) + return 0; /* too many conditional branches found, fallback to the standard single-step code. */ if (absolute) - breaks[1] = immediate; + breaks[last_breakpoint] = immediate; else - breaks[1] = loc + immediate; + breaks[last_breakpoint] = loc + immediate; - bc_insn_count++; last_breakpoint++; } @@ -1146,18 +1141,29 @@ ppc_deal_with_atomic_sequence (struct fr insn = read_memory_integer (loc, PPC_INSN_SIZE, byte_order); /* Insert a breakpoint right after the end of the atomic sequence. */ - breaks[0] = loc; + breaks[last_breakpoint] = loc; - /* Check for duplicated breakpoints. Check also for a breakpoint - placed (branch instruction's destination) anywhere in sequence. */ - if (last_breakpoint - && (breaks[1] == breaks[0] - || (breaks[1] >= pc && breaks[1] <= closing_insn))) - last_breakpoint = 0; - - /* Effectively inserts the breakpoints. */ for (index = 0; index <= last_breakpoint; index++) - insert_single_step_breakpoint (gdbarch, aspace, breaks[index]); + { + int index2; + int insert_bp = 1; + + /* Check for a breakpoint placed (branch instruction's destination) + anywhere in sequence. */ + if (breaks[index] >= pc && breaks[index] <= closing_insn) + continue; + + /* Check for duplicated breakpoints. */ + for (index2 = 0; index2 < index; index2++) + { + if (breaks[index] == breaks[index2]) + insert_bp = 0; + } + + /* insert the breakpoint. */ + if (insert_bp) + insert_single_step_breakpoint (gdbarch, aspace, breaks[index]); + } return 1; } Index: b/gdb/breakpoint.c =================================================================== --- a/gdb/breakpoint.c +++ b/gdb/breakpoint.c @@ -14741,11 +14741,10 @@ deprecated_remove_raw_breakpoint (struct return ret; } -/* One (or perhaps two) breakpoints used for software single - stepping. */ +/* Breakpoints used for software single stepping. */ -static void *single_step_breakpoints[2]; -static struct gdbarch *single_step_gdbarch[2]; +static void *single_step_breakpoints[MAX_SINGLE_STEP_BREAKPOINTS]; +static struct gdbarch *single_step_gdbarch[MAX_SINGLE_STEP_BREAKPOINTS]; /* Create and insert a breakpoint for software single step. */ @@ -14754,19 +14753,17 @@ insert_single_step_breakpoint (struct gd struct address_space *aspace, CORE_ADDR next_pc) { + int i; void **bpt_p; - if (single_step_breakpoints[0] == NULL) - { - bpt_p = &single_step_breakpoints[0]; - single_step_gdbarch[0] = gdbarch; - } - else - { - gdb_assert (single_step_breakpoints[1] == NULL); - bpt_p = &single_step_breakpoints[1]; - single_step_gdbarch[1] = gdbarch; - } + for (i = 0; i < MAX_SINGLE_STEP_BREAKPOINTS; i++) + if (single_step_breakpoints[i] == NULL) + break; + + gdb_assert (i < MAX_SINGLE_STEP_BREAKPOINTS); + + bpt_p = &single_step_breakpoints[i]; + single_step_gdbarch[i] = gdbarch; /* NOTE drow/2006-04-11: A future improvement to this function would be to only create the breakpoints once, and actually put them on @@ -14787,8 +14784,13 @@ insert_single_step_breakpoint (struct gd int single_step_breakpoints_inserted (void) { - return (single_step_breakpoints[0] != NULL - || single_step_breakpoints[1] != NULL); + int i; + + for (i = 0; i < MAX_SINGLE_STEP_BREAKPOINTS; i++) + if (single_step_breakpoints[i] != NULL) + return 1; + + return 0; } /* Remove and delete any breakpoints used for software single step. */ @@ -14796,22 +14798,21 @@ single_step_breakpoints_inserted (void) void remove_single_step_breakpoints (void) { + int i; + gdb_assert (single_step_breakpoints[0] != NULL); /* See insert_single_step_breakpoint for more about this deprecated call. */ - deprecated_remove_raw_breakpoint (single_step_gdbarch[0], - single_step_breakpoints[0]); - single_step_gdbarch[0] = NULL; - single_step_breakpoints[0] = NULL; - if (single_step_breakpoints[1] != NULL) - { - deprecated_remove_raw_breakpoint (single_step_gdbarch[1], - single_step_breakpoints[1]); - single_step_gdbarch[1] = NULL; - single_step_breakpoints[1] = NULL; - } + for (i = 0; i < MAX_SINGLE_STEP_BREAKPOINTS; i++) + if (single_step_breakpoints[i] != NULL) + { + deprecated_remove_raw_breakpoint (single_step_gdbarch[i], + single_step_breakpoints[i]); + single_step_gdbarch[i] = NULL; + single_step_breakpoints[i] = NULL; + } } /* Delete software single step breakpoints without removing them from @@ -14824,7 +14825,7 @@ cancel_single_step_breakpoints (void) { int i; - for (i = 0; i < 2; i++) + for (i = 0; i < MAX_SINGLE_STEP_BREAKPOINTS; i++) if (single_step_breakpoints[i]) { xfree (single_step_breakpoints[i]); @@ -14841,7 +14842,7 @@ detach_single_step_breakpoints (void) { int i; - for (i = 0; i < 2; i++) + for (i = 0; i < MAX_SINGLE_STEP_BREAKPOINTS; i++) if (single_step_breakpoints[i]) target_remove_breakpoint (single_step_gdbarch[i], single_step_breakpoints[i]); @@ -14856,7 +14857,7 @@ single_step_breakpoint_inserted_here_p ( { int i; - for (i = 0; i < 2; i++) + for (i = 0; i < MAX_SINGLE_STEP_BREAKPOINTS; i++) { struct bp_target_info *bp_tgt = single_step_breakpoints[i]; if (bp_tgt Index: b/gdb/breakpoint.h =================================================================== --- a/gdb/breakpoint.h +++ b/gdb/breakpoint.h @@ -1408,8 +1408,10 @@ extern int is_catchpoint (struct breakpo deletes all breakpoints. */ extern void delete_command (char *arg, int from_tty); -/* Manage a software single step breakpoint (or two). Insert may be - called twice before remove is called. */ +/* Manage software single step breakpoints. Insert may be + called multiple times before remove is called. */ +#define MAX_SINGLE_STEP_BREAKPOINTS 4 + extern void insert_single_step_breakpoint (struct gdbarch *, struct address_space *, CORE_ADDR);