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[PATCH v2, alpha]: Handle single-stepping of atomic sequences
- From: Uros Bizjak <ubizjak at gmail dot com>
- To: gdb-patches at sourceware dot org
- Cc: Alan Modra <amodra at gmail dot com>, Richard Henderson <rth at redhat dot com>
- Date: Fri, 18 Nov 2011 13:18:57 +0100
- Subject: [PATCH v2, alpha]: Handle single-stepping of atomic sequences
- References: <CAFULd4Ysi5pmL6AHNsvy2qAEk4_WrEo4vLKQvgHgvXXqd1-TRg@mail.gmail.com>
On Wed, Nov 16, 2011 at 11:47 PM, Uros Bizjak <ubizjak@gmail.com> wrote:
> The gcc simulate-thread.exp testsuite exposed the problem in handling
> of alpha atomic sequences. Single-stepping broke link in alpha's LL/SC
> atomic sequences.
>
> Attached patch copies handling of atomic sequences from rs6000-tdep.c
> and adapts the functionality for alpha.
>
> 2011-11-16 ?Uros Bizjak ?<ubizjak@gmail.com>
>
> ? ? ? ?* alpha-tdep.c (beq_opcode): New.
> ? ? ? ?(ldl_l_opcode, ldq_l_opcode, stl_c_opcode, stq_c_opcode): Ditto.
> ? ? ? ?(alpha_deal_with_atomic_sequence): New function.
> ? ? ? ?(alpha_gdbarch_init): Handle single stepping of atomic sequences
> ? ? ? ?with alpha_deal_with_atomic_sequence.
>
> Patched gdb survives simulate-thread.exp testsuite on native
> alphaev68-pc-linux-gnu.
>
> I don't have write access, so If OK, please someone commit this patch
> to gdb CVS.
[v2]: Since this patch is almost a copy of rs6000-tdep.c atomic
sequence handling, also take into account proposed changes [1] to
original rs6000 implementation.
[1] http://sourceware.org/ml/gdb-patches/2011-11/msg00468.html
Uros,
--- alpha-tdep.c 2011-11-18 12:20:08.000000000 +0100
+++ alpha-tdep.c.ub 2011-11-18 12:18:37.000000000 +0100
@@ -65,6 +65,7 @@ static const int stq_opcode = 0x2d;
/* Branch instruction format */
#define BR_RA(insn) MEM_RA(insn)
+static const int beq_opcode = 0x39;
static const int bne_opcode = 0x3d;
/* Operate instruction format */
@@ -762,6 +763,94 @@ alpha_skip_prologue (struct gdbarch *gdb
}
+static const int ldl_l_opcode = 0x2a;
+static const int ldq_l_opcode = 0x2b;
+static const int stl_c_opcode = 0x2e;
+static const int stq_c_opcode = 0x2f;
+
+/* Checks for an atomic sequence of instructions beginning with a LDL_L/LDQ_L
+ instruction and ending with a STL_C/STQ_C instruction. If such a sequence
+ is found, attempt to step through it. A breakpoint is placed at the end of
+ the sequence. */
+
+int
+alpha_deal_with_atomic_sequence (struct frame_info *frame)
+{
+ struct gdbarch *gdbarch = get_frame_arch (frame);
+ struct address_space *aspace = get_frame_address_space (frame);
+ CORE_ADDR pc = get_frame_pc (frame);
+ CORE_ADDR breaks[2] = {-1, -1};
+ CORE_ADDR loc = pc;
+ CORE_ADDR closing_insn; /* Instruction that closes the atomic sequence. */
+ unsigned int insn = alpha_read_insn (gdbarch, loc);
+ int insn_count;
+ int index;
+ int last_breakpoint = 0; /* Defaults to 0 (no breakpoints placed). */
+ const int atomic_sequence_length = 16; /* Instruction sequence length. */
+ int bc_insn_count = 0; /* Conditional branch instruction count. */
+
+ /* Assume all atomic sequences start with a LDL_L/LDQ_L instruction. */
+ if (INSN_OPCODE (insn) != ldl_l_opcode
+ && INSN_OPCODE (insn) != ldq_l_opcode)
+ return 0;
+
+ /* Assume that no atomic sequence is longer than "atomic_sequence_length"
+ instructions. */
+ for (insn_count = 0; insn_count < atomic_sequence_length; ++insn_count)
+ {
+ loc += ALPHA_INSN_SIZE;
+ insn = alpha_read_insn (gdbarch, loc);
+
+ /* 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_OPCODE (insn) >= beq_opcode)
+ {
+ int immediate = (insn & 0x001fffff) << 2;
+
+ immediate = (immediate ^ 0x400000) - 0x400000;
+
+ if (bc_insn_count >= 1)
+ return 0; /* More than one conditional branch found, fallback
+ to the standard single-step code. */
+
+ breaks[1] = loc + ALPHA_INSN_SIZE + immediate;
+
+ bc_insn_count++;
+ last_breakpoint++;
+ }
+
+ if (INSN_OPCODE (insn) == stl_c_opcode
+ || INSN_OPCODE (insn) == stq_c_opcode)
+ break;
+ }
+
+ /* Assume that the atomic sequence ends with a STL_C/STQ_C instruction. */
+ if (INSN_OPCODE (insn) != stl_c_opcode
+ && INSN_OPCODE (insn) != stq_c_opcode)
+ return 0;
+
+ closing_insn = loc;
+ loc += ALPHA_INSN_SIZE;
+
+ /* Insert a breakpoint right after the end of the atomic sequence. */
+ breaks[0] = 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]);
+
+ return 1;
+}
+
+
/* Figure out where the longjmp will land.
We expect the first arg to be a pointer to the jmp_buf structure from
which we extract the PC (JB_PC) that we will land at. The PC is copied
@@ -1749,6 +1838,9 @@ alpha_gdbarch_init (struct gdbarch_info
set_gdbarch_decr_pc_after_break (gdbarch, ALPHA_INSN_SIZE);
set_gdbarch_cannot_step_breakpoint (gdbarch, 1);
+ /* Handles single stepping of atomic sequences. */
+ set_gdbarch_software_single_step (gdbarch, alpha_deal_with_atomic_sequence);
+
/* Hook in ABI-specific overrides, if they have been registered. */
gdbarch_init_osabi (info, gdbarch);