[PATCH 2/2] gdb: Add support for DW_LNS_set_prologue_end in line-table

[Lancelot SIX <lancelot.six@amd.com>]

Add support for DW_LNS_set_prologue_end when building line-tables.  This
attribute can be set by the compiler to indicate that an instruction is
an adequate place to set a breakpoint just after the prologue of a
function.

The compiler might set multiple prologue_end, but considering how
current skip_prologue_using_sal works, this commit modifies it to accept
the first instruction with this marker (if any) to be the place where to
a breakpoint should be placed to be at the end of the prologue.

The need for this support came from a problematic usecase generated by
hipcc (i.e. clang).  The problem is as follows:  There's a function
(lets call it foo) which covers PC from 0xa800 to 0xa950.  The body of
foo begins with a call to an inlined function, covering from 0xa800 to
0xa94c.   The issue is that when placing a breakpoint at 'foo', GDB
inserts the breakpoint at 0xa818.  The 0x18 offset is what GDB thinks is
foo's first address past the prologue.

Later, when hitting the breakpoint, GDB reports the stop within the
inlined function because the PC falls in its range while the user
expects to stop in FOO.

Looking at the line-table for this location, we have:

    INDEX  LINE   ADDRESS            IS-STMT
    [...]
    14     293    0x000000000000a66c Y
    15     END    0x000000000000a6e0 Y
    16     287    0x000000000000a800 Y
    17     END    0x000000000000a818 Y
    18     287    0x000000000000a824 Y
    [...]

For comparison, let's look at llvm-dwarfdump's output for this CU:

    Address            Line   Column File   ISA Discriminator Flags
    ------------------ ------ ------ ------ --- ------------- -------------
    [...]
    0x000000000000a66c    293     12      2   0             0  is_stmt
    0x000000000000a6e0     96     43     82   0             0  is_stmt
    0x000000000000a6f8    102     18     82   0             0  is_stmt
    0x000000000000a70c    102     24     82   0             0
    0x000000000000a710    102     18     82   0             0
    0x000000000000a72c    101     16     82   0             0  is_stmt
    0x000000000000a73c   2915     50     83   0             0  is_stmt
    0x000000000000a74c    110      1      1   0             0  is_stmt
    0x000000000000a750    110      1      1   0             0  is_stmt end_sequence
    0x000000000000a800    107      0      1   0             0  is_stmt
    0x000000000000a800    287     12      2   0             0  is_stmt prologue_end
    0x000000000000a818    114     59     81   0             0  is_stmt
    0x000000000000a824    287     12      2   0             0  is_stmt
    0x000000000000a828    100     58     82   0             0  is_stmt
    [...]

The main difference we are interested in here is that llvm-dwarfdump's
output tells us that 0xa800 is an adequate place to place a breakpoint
past a function prologue.  Since we know that foo starts at covers from
0xa800 to 0xa94c, 0xa800 is the address at which the breakpoint should
be placed if the user wants to break in foo.

This commit proposes to add support for the prologue_end tag in the
line-program processing.

The processing of this prologue_end flag is made in skip_prologue_sal,
before it calls gdbarch_skip_prologue_noexcept.  The intent is that if
the compiler gave information on where the prologue ends, we should use
this information before and not try to rely on architecture dependent
logic to guess it.

The testsuite have been executed using this patch on GNU/Linux x86_64.
Testcases have been combiled with both gcc/g++ and clang/clang++ since
GCC does not set the prologue_end marker.  No regression have been
observed with GCC or Clang.  Note that when using Clang, this patch
fixes a failure in gdb.opt/inline-small-func.exp.

Change-Id: I720449a8a9b2e1fb45b54c6095d3b1e9da9152f8
---
 gdb/NEWS                                      |  4 +
 gdb/buildsym.c                                |  1 +
 gdb/buildsym.h                                |  1 +
 gdb/doc/gdb.texinfo                           | 27 ++++++
 gdb/dwarf2/read.c                             | 15 ++-
 gdb/symmisc.c                                 |  6 +-
 gdb/symtab.c                                  | 51 +++++++++++
 gdb/symtab.h                                  |  4 +
 .../dw2-out-of-range-end-of-seq.exp           |  4 +-
 gdb/testsuite/gdb.dwarf2/dw2-prologue-end.c   | 28 ++++++
 gdb/testsuite/gdb.dwarf2/dw2-prologue-end.exp | 91 +++++++++++++++++++
 gdb/testsuite/gdb.dwarf2/dw2-ranges-base.exp  |  2 +-
 gdb/testsuite/lib/dwarf.exp                   | 16 ++--
 13 files changed, 238 insertions(+), 12 deletions(-)
 create mode 100644 gdb/testsuite/gdb.dwarf2/dw2-prologue-end.c
 create mode 100644 gdb/testsuite/gdb.dwarf2/dw2-prologue-end.exp

diff --git a/gdb/NEWS b/gdb/NEWS
index c609da7e6cf..89811219f59 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -3,6 +3,10 @@
 
 *** Changes since GDB 11
 
+* GDB now honours the DWARF prologue_end line-table entry flag the compiler can
+  emit to indicate where a breakpoint should be placed to break in a function
+  past its prologue.
+
 * DBX mode is deprecated, and will be removed in GDB 13
 
 * GDB 12 is the last release of GDB that will support building against
diff --git a/gdb/buildsym.c b/gdb/buildsym.c
index a875eb5ce38..0b8bbe21a01 100644
--- a/gdb/buildsym.c
+++ b/gdb/buildsym.c
@@ -725,6 +725,7 @@ buildsym_compunit::record_line (struct subfile *subfile, int line,
   e->line = line;
   e->is_stmt = (flags & LEF_IS_STMT) != 0;
   e->pc = pc;
+  e->prologue_end = (flags & LEF_PROLOGUE_END) != 0;
 }
 
 \f
diff --git a/gdb/buildsym.h b/gdb/buildsym.h
index 09c2d563ec9..252bad187dc 100644
--- a/gdb/buildsym.h
+++ b/gdb/buildsym.h
@@ -115,6 +115,7 @@ struct context_stack
 enum linetable_entry_flag : unsigned
 {
   LEF_IS_STMT = 1 << 1,
+  LEF_PROLOGUE_END = 1 << 2,
 };
 DEF_ENUM_FLAGS_TYPE (enum linetable_entry_flag, linetable_entry_flags);
 
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 729f9d79a93..568ac86f6fd 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -19794,6 +19794,33 @@ line 1574.
 List the @code{struct linetable} from all @code{struct symtab}
 instances whose name matches @var{regexp}.  If @var{regexp} is not
 given, list the @code{struct linetable} from all @code{struct symtab}.
+For example:
+
+@smallexample
+(@value{GDBP}) maint info line-table
+objfile: /home/gnu/build/a.out ((struct objfile *) 0x6120000e0d40)
+compunit_symtab: simple.cpp ((struct compunit_symtab *) 0x6210000ff450)
+symtab: /home/gnu/src/simple.cpp ((struct symtab *) 0x6210000ff4d0)
+linetable: ((struct linetable *) 0x62100012b760):
+INDEX  LINE   ADDRESS            IS-STMT PROLOGUE-END
+0      3      0x0000000000401110 Y
+1      4      0x0000000000401114 Y       Y
+2      9      0x0000000000401120 Y
+3      10     0x0000000000401124 Y       Y
+4      10     0x0000000000401129
+5      15     0x0000000000401130 Y
+6      16     0x0000000000401134 Y       Y
+7      16     0x0000000000401139
+8      21     0x0000000000401140 Y
+9      22     0x000000000040114f Y       Y
+10     22     0x0000000000401154
+11     END    0x000000000040115a Y
+@end smallexample
+@noindent
+The @var{IS-STMT} column indicates if the address is a recommended breakpoint
+location to represent a line or a statement.  The @var{PROLOGUE-END} column
+indicates that a given address is an adequate to place a breakpoint at the
+first instruction following a function prologue.
 
 @kindex maint set symbol-cache-size
 @cindex symbol cache size
diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index e470fc6fd5d..3905555e6d4 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -20901,6 +20901,7 @@ class lnp_state_machine
   {
     record_line (false);
     m_discriminator = 0;
+    m_flags &= ~LEF_PROLOGUE_END;
   }
 
   /* Handle DW_LNE_end_sequence.  */
@@ -20909,6 +20910,12 @@ class lnp_state_machine
     m_currently_recording_lines = true;
   }
 
+  /* Handle DW_LNS_set_prologue_end.  */
+  void handle_set_prologue_end ()
+  {
+    m_flags |= LEF_PROLOGUE_END;
+  }
+
 private:
   /* Advance the line by LINE_DELTA.  */
   void advance_line (int line_delta)
@@ -21000,6 +21007,7 @@ lnp_state_machine::handle_special_opcode (unsigned char op_code)
   advance_line (line_delta);
   record_line (false);
   m_discriminator = 0;
+  m_flags &= ~LEF_PROLOGUE_END;
 }
 
 void
@@ -21137,10 +21145,12 @@ lnp_state_machine::record_line (bool end_sequence)
     {
       fprintf_unfiltered (gdb_stdlog,
 			  "Processing actual line %u: file %u,"
-			  " address %s, is_stmt %u, discrim %u%s\n",
+			  " address %s, is_stmt %u, prologue_end %u,"
+			  " discrim %u%s\n",
 			  m_line, m_file,
 			  paddress (m_gdbarch, m_address),
 			  (m_flags & LEF_IS_STMT) != 0,
+			  (m_flags & LEF_PROLOGUE_END) != 0,
 			  m_discriminator,
 			  (end_sequence ? "\t(end sequence)" : ""));
     }
@@ -21463,6 +21473,9 @@ dwarf_decode_lines_1 (struct line_header *lh, struct dwarf2_cu *cu,
 		state_machine.handle_fixed_advance_pc (addr_adj);
 	      }
 	      break;
+	    case DW_LNS_set_prologue_end:
+	      state_machine.handle_set_prologue_end ();
+	      break;
 	    default:
 	      {
 		/* Unknown standard opcode, ignore it.  */
diff --git a/gdb/symmisc.c b/gdb/symmisc.c
index 114d6bc5e53..bef477e5854 100644
--- a/gdb/symmisc.c
+++ b/gdb/symmisc.c
@@ -982,11 +982,12 @@ maintenance_print_one_line_table (struct symtab *symtab, void *data)
       /* Leave space for 6 digits of index and line number.  After that the
 	 tables will just not format as well.  */
       struct ui_out *uiout = current_uiout;
-      ui_out_emit_table table_emitter (uiout, 4, -1, "line-table");
+      ui_out_emit_table table_emitter (uiout, 5, -1, "line-table");
       uiout->table_header (6, ui_left, "index", _("INDEX"));
       uiout->table_header (6, ui_left, "line", _("LINE"));
       uiout->table_header (18, ui_left, "address", _("ADDRESS"));
-      uiout->table_header (1, ui_left, "is-stmt", _("IS-STMT"));
+      uiout->table_header (7, ui_left, "is-stmt", _("IS-STMT"));
+      uiout->table_header (12, ui_left, "prologue-end", _("PROLOGUE-END"));
       uiout->table_body ();
 
       for (int i = 0; i < linetable->nitems; ++i)
@@ -1003,6 +1004,7 @@ maintenance_print_one_line_table (struct symtab *symtab, void *data)
 	  uiout->field_core_addr ("address", objfile->arch (),
 				  item->pc);
 	  uiout->field_string ("is-stmt", item->is_stmt ? "Y" : "");
+	  uiout->field_string ("prologue-end", item->prologue_end ? "Y" : "");
 	  uiout->text ("\n");
 	}
     }
diff --git a/gdb/symtab.c b/gdb/symtab.c
index a867e1db9fd..2f0884b7b31 100644
--- a/gdb/symtab.c
+++ b/gdb/symtab.c
@@ -3818,6 +3818,42 @@ skip_prologue_using_lineinfo (CORE_ADDR func_addr, struct symtab *symtab)
   return func_addr;
 }
 
+/* Try to locate the address where a breakpoint should be placed past the
+   prologue of function starting at FUNC_ADDR using the line table.
+
+   Return the address associated with the first entry in the line-table for
+   the function starting at FUNC_ADDR which has prologue_end set to true if
+   such entry exist, otherwise return an empty optional.  */
+
+static gdb::optional<CORE_ADDR>
+skip_prologue_using_linetable (CORE_ADDR func_addr)
+{
+  CORE_ADDR start_pc, end_pc;
+
+  if (!find_pc_partial_function (func_addr, nullptr, &start_pc, &end_pc))
+    return {};
+
+  const struct symtab_and_line prologue_sal = find_pc_line (start_pc, 0);
+  if (prologue_sal.symtab != nullptr
+      && prologue_sal.symtab->language () != language_asm)
+    {
+      struct linetable *linetable = prologue_sal.symtab->linetable ();
+
+      auto it = std::lower_bound
+	(linetable->item, linetable->item + linetable->nitems, start_pc,
+	 [] (const linetable_entry &lte, CORE_ADDR pc) -> bool
+	 { return lte.pc < pc; });
+
+      for (;
+	   it < linetable->item + linetable->nitems && it->pc <= end_pc ;
+	   it++)
+	if (it->prologue_end)
+	  return {it->pc};
+    }
+
+  return {};
+}
+
 /* Adjust SAL to the first instruction past the function prologue.
    If the PC was explicitly specified, the SAL is not changed.
    If the line number was explicitly specified then the SAL can still be
@@ -3901,6 +3937,21 @@ skip_prologue_sal (struct symtab_and_line *sal)
     {
       pc = saved_pc;
 
+      /* Check if the compiler explicitely indicated where a breakpoint should
+         be placed to skip the prologue.  */
+      if (skip)
+	{
+	  gdb::optional<CORE_ADDR> linetable_pc
+	    = skip_prologue_using_linetable (pc);
+	  if (linetable_pc)
+	    {
+	      pc = *linetable_pc;
+	      start_sal = find_pc_sect_line (pc, section, 0);
+	      force_skip = 1;
+	      continue;
+	    }
+	}
+
       /* If the function is in an unmapped overlay, use its unmapped LMA address,
 	 so that gdbarch_skip_prologue has something unique to work on.  */
       if (section_is_overlay (section) && !section_is_mapped (section))
diff --git a/gdb/symtab.h b/gdb/symtab.h
index d12eee6e9d8..25b4f7d2704 100644
--- a/gdb/symtab.h
+++ b/gdb/symtab.h
@@ -1398,6 +1398,10 @@ struct linetable_entry
   /* True if this PC is a good location to place a breakpoint for LINE.  */
   unsigned is_stmt : 1;
 
+  /* True if this location is a good location to place a breakpoint after a
+     function prologue.  */
+  bool prologue_end : 1;
+
   /* The address for this entry.  */
   CORE_ADDR pc;
 };
diff --git a/gdb/testsuite/gdb.dwarf2/dw2-out-of-range-end-of-seq.exp b/gdb/testsuite/gdb.dwarf2/dw2-out-of-range-end-of-seq.exp
index f60f622067e..23df111e73a 100644
--- a/gdb/testsuite/gdb.dwarf2/dw2-out-of-range-end-of-seq.exp
+++ b/gdb/testsuite/gdb.dwarf2/dw2-out-of-range-end-of-seq.exp
@@ -86,10 +86,10 @@ if ![runto_main] {
 
 set test "END with address 1 eliminated"
 gdb_test_multiple "maint info line-table $srcfile$" $test {
-    -re -wrap "END *0x0*1 *Y \r\n.*" {
+    -re -wrap "END *0x0*1 *Y *\r\n.*" {
 	fail $gdb_test_name
     }
-    -re -wrap "END *$hex *Y " {
+    -re -wrap "END *$hex *Y *" {
 	pass $gdb_test_name
     }
 }
diff --git a/gdb/testsuite/gdb.dwarf2/dw2-prologue-end.c b/gdb/testsuite/gdb.dwarf2/dw2-prologue-end.c
new file mode 100644
index 00000000000..d166540d9b3
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/dw2-prologue-end.c
@@ -0,0 +1,28 @@
+/* Copyright 2022 Free Software Foundation, Inc.
+
+   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 <http://www.gnu.org/licenses/>.  */
+
+
+int
+main (void)
+{							/* main prologue */
+  asm ("main_label: .global main_label");
+  int m = 42;						/* main assign m */
+  asm ("main_assign_n: .global main_assign_n");
+  int n = 54;						/* main assign n */
+  asm ("main_end_prologue: .global main_end_prologue");
+  int o = 96;						/* main assign o */
+  asm ("main_end: .global main_end");			/* main end */
+  return m + n - o;
+}
diff --git a/gdb/testsuite/gdb.dwarf2/dw2-prologue-end.exp b/gdb/testsuite/gdb.dwarf2/dw2-prologue-end.exp
new file mode 100644
index 00000000000..0de13ae680d
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/dw2-prologue-end.exp
@@ -0,0 +1,91 @@
+# Copyright 2022 Free Software Foundation, Inc.
+
+# 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 <http://www.gnu.org/licenses/>.
+
+# Check that GDB can honor the prologue_end flag the compiler can place
+# in the line-table data.
+
+load_lib dwarf.exp
+
+# This test can only be run on targets which support DWARF-2 and use gas.
+if {![dwarf2_support]} {
+    return 0
+}
+
+standard_testfile .c .S
+
+set asm_file [standard_output_file $srcfile2]
+Dwarf::assemble $asm_file {
+    global srcdir subdir srcfile srcfile2
+    declare_labels lines_label
+
+    get_func_info main
+
+    cu {} {
+	compile_unit {
+	    {language @DW_LANG_C}
+	    {name dw2-prologue-end.c}
+	    {stmt_list ${lines_label} DW_FORM_sec_offset}
+	} {
+	    subprogram {
+		{external 1 flag}
+		{name main}
+		{low_pc $main_start addr}
+		{high_pc "$main_start + $main_len" addr}
+	    }
+	}
+    }
+
+    lines {version 5} lines_label {
+	include_dir "${srcdir}/${subdir}"
+	file_name "$srcfile" 1
+
+	program {
+	    {DW_LNE_set_address $main_start}
+	    {line [gdb_get_line_number "main prologue"]}
+	    {DW_LNS_copy}
+
+	    {DW_LNE_set_address main_label}
+	    {line [gdb_get_line_number "main assign m"]}
+	    {DW_LNS_copy}
+
+	    {DW_LNE_set_address main_assign_n}
+	    {line [gdb_get_line_number "main assign n"]}
+	    {DW_LNS_copy}
+
+	    {DW_LNE_set_address main_end_prologue}
+	    {line [gdb_get_line_number "main assign o"]}
+	    {DW_LNS_set_prologue_end}
+	    {DW_LNS_copy}
+
+	    {DW_LNE_set_address main_end}
+	    {line [gdb_get_line_number "main end"]}
+	    {DW_LNS_copy}
+
+	    {DW_LNE_end_sequence}
+	}
+    }
+}
+
+if { [prepare_for_testing "failed to prepare" ${testfile} \
+	  [list $srcfile $asm_file] {nodebug}] } {
+    return -1
+}
+
+if ![runto_main] {
+    return -1
+}
+
+set prologue_end_line [gdb_get_line_number "main assign o"]
+gdb_test "frame" ".*main \\\(\\\) at \[^\r\n\]*:$prologue_end_line\r\n.*"
diff --git a/gdb/testsuite/gdb.dwarf2/dw2-ranges-base.exp b/gdb/testsuite/gdb.dwarf2/dw2-ranges-base.exp
index ae44dc49329..ec31f1f9d23 100644
--- a/gdb/testsuite/gdb.dwarf2/dw2-ranges-base.exp
+++ b/gdb/testsuite/gdb.dwarf2/dw2-ranges-base.exp
@@ -183,7 +183,7 @@ gdb_test_multiple "maint info line-table gdb.dwarf2/dw2-ranges-base.c" \
 	-re ".*linetable: \\(\\(struct linetable \\*\\) 0x0\\):\r\nNo line table.\r\n" {
 	    exp_continue
 	}
-	-re ".*linetable: \\(\\(struct linetable \\*\\) $hex\\):\r\nINDEX\[ \t\]+LINE\[ \t\]+ADDRESS\[ \t\]+IS-STMT *\r\n" {
+	-re ".*linetable: \\(\\(struct linetable \\*\\) $hex\\):\r\nINDEX\[ \t\]+LINE\[ \t\]+ADDRESS\[ \t\]+IS-STMT\[ \t\]PROLOGUE-END *\r\n" {
 	    exp_continue
 	}
     }
diff --git a/gdb/testsuite/lib/dwarf.exp b/gdb/testsuite/lib/dwarf.exp
index 6e8b1ccbe7f..ed7ad383180 100644
--- a/gdb/testsuite/lib/dwarf.exp
+++ b/gdb/testsuite/lib/dwarf.exp
@@ -2269,14 +2269,13 @@ namespace eval Dwarf {
 	_op .byte $_default_is_stmt "default_is_stmt"
 	_op .byte 1 "line_base"
 	_op .byte 1 "line_range"
-	_op .byte 10 "opcode_base"
+	_op .byte 11 "opcode_base"
 
 	# The standard_opcode_lengths table.  The number of arguments
-	# for each of the standard opcodes.  Generating 9 entries here
-	# matches the use of 10 in the opcode_base above.  These 9
-	# entries match the 9 standard opcodes for DWARF2, making use
-	# of only 9 should be fine, even if we are generating DWARF3
-	# or DWARF4.
+	# for each of the standard opcodes.  Generating 10 entries here
+	# matches the use of 11 in the opcode_base above.  These 10
+	# entries match the 9 standard opcodes for DWARF2 plus
+	# DW_LNS_prologue_end from DWARF3.
 	_op .byte 0 "standard opcode 1"
 	_op .byte 1 "standard opcode 2"
 	_op .byte 1 "standard opcode 3"
@@ -2286,6 +2285,7 @@ namespace eval Dwarf {
 	_op .byte 0 "standard opcode 7"
 	_op .byte 0 "standard opcode 8"
 	_op .byte 1 "standard opcode 9"
+	_op .byte 0 "standard opcode 10"
 
 	proc include_dir {dirname} {
 	    variable _line_include_dirs
@@ -2481,6 +2481,10 @@ namespace eval Dwarf {
 		_op .byte 6
 	    }
 
+	    proc DW_LNS_set_prologue_end {} {
+		_op .byte 0x0a
+	    }
+
 	    proc DW_LNS_advance_pc {offset} {
 		_op .byte 2
 		_op .uleb128 ${offset}
-- 
2.25.1