[gdb/symtab] Support .debug_line with DW_FORM_line_strp

I noticed a new gcc option -gdwarf64 and tried it out (using gcc 11.2.1).

With a test-case hello.c:
...
int
main (void)
{
  printf ("hello\n");
  return 0;
}
...
compiled like this:
...
$ gcc -g -gdwarf64 ~/hello.c
...
I ran into:
...
$ gdb -q -batch a.out
DW_FORM_line_strp pointing outside of .debug_line_str section \
  [in module a.out]
...

Debugging gdb revealed that the string offset is:
...
(gdb) up
    objfile=0x182ab70, str_offset=1378684502312,
    form_name=0xeae9b5 "DW_FORM_line_strp")
    at src/gdb/dwarf2/section.c:208
208         error (_("%s pointing outside of %s section [in module %s]"),
(gdb) p /x str_offset
$1 = 0x14100000128
(gdb)
...
which is read when parsing a .debug_line entry at 0x1e0.

Looking with readelf at the 0x1e0 entry, we have:
...
 The Directory Table (offset 0x202, lines 2, columns 1):
  Entry Name
  0     (indirect line string, offset: 0x128): /data/gdb_versions/devel
  1     (indirect line string, offset: 0x141): /home/vries
...
which in a hexdump looks like:
...
  0x00000200 1f022801 00004101 00000201 1f020f02
...

What happens is the following:
- readelf interprets the DW_FORM_line_strp reference to .debug_line_str as
  a 4 byte value, and sees entries 0x00000128 and 0x00000141.
- gdb instead interprets it as an 8 byte value, and sees as first entry
  0x0000014100000128, which is too big so it bails out.

AFAIU, gdb is wrong.  It assumes DW_FORM_line_strp is 8 bytes on the basis
that the corresponding CU is 64-bit DWARF.  However, the .debug_line
contribution has it's own initial_length field, and encodes there that it's
32-bit DWARF.

Fix this by using the correct offset size for DW_FORM_line_strp references
in .debug_line.

Note: the described test-case does trigger this complaint (both with and
without this patch):
...
$ gdb -q -batch -iex "set complaints 10" a.out
During symbol reading: intermixed 32-bit and 64-bit DWARF sections
...

The reason that the CU has 64-bit dwarf is because -gdwarf64 was passed to
gcc.  The reason that the .debug_line entry has 32-bit dwarf is because that's
what gas generates.  Perhaps this is complaint-worthy, but I don't think it
is wrong.

Tested on x86_64-linux, using native and target board dwarf64.exp.

diff --git a/gdb/dwarf2/line-header.c b/gdb/dwarf2/line-header.c
index 15195764c898e3427914039e72fc4c0ce232b029..852e2851e99437a91d0a194935d9d60c59697f7c 100644 (file)
--- a/gdb/dwarf2/line-header.c
+++ b/gdb/dwarf2/line-header.c
@@ -137,7 +137,7 @@ read_checked_initial_length_and_offset (bfd *abfd, const gdb_byte *buf,
 static void
 read_formatted_entries (dwarf2_per_objfile *per_objfile, bfd *abfd,
                        const gdb_byte **bufp, struct line_header *lh,
-                       const struct comp_unit_head *cu_header,
+                       unsigned int offset_size,
                        void (*callback) (struct line_header *lh,
                                          const char *name,
                                          dir_index d_index,
@@ -187,9 +187,12 @@ read_formatted_entries (dwarf2_per_objfile *per_objfile, bfd *abfd,
              break;
 
            case DW_FORM_line_strp:
-             string.emplace
-               (per_objfile->read_line_string (buf, cu_header, &bytes_read));
-             buf += bytes_read;
+             {
+               const char *str
+                 = per_objfile->read_line_string (buf, offset_size);
+               string.emplace (str);
+               buf += offset_size;
+             }
              break;
 
            case DW_FORM_data1:
@@ -372,7 +375,7 @@ dwarf_decode_line_header  (sect_offset sect_off, bool is_dwz,
     {
       /* Read directory table.  */
       read_formatted_entries (per_objfile, abfd, &line_ptr, lh.get (),
-                             cu_header,
+                             offset_size,
                              [] (struct line_header *header, const char *name,
                                  dir_index d_index, unsigned int mod_time,
                                  unsigned int length)
@@ -382,7 +385,7 @@ dwarf_decode_line_header  (sect_offset sect_off, bool is_dwz,
 
       /* Read file name table.  */
       read_formatted_entries (per_objfile, abfd, &line_ptr, lh.get (),
-                             cu_header,
+                             offset_size,
                              [] (struct line_header *header, const char *name,
                                  dir_index d_index, unsigned int mod_time,
                                  unsigned int length)

diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index 4a963e4a236bae75a95883da1e72612c8894f4f1..a513cc493a78786746c8d022947c9449f4b686bc 100644 (file)
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -20304,6 +20304,18 @@ read_indirect_string (dwarf2_per_objfile *per_objfile, bfd *abfd,
 
 /* See read.h.  */
 
+const char *
+dwarf2_per_objfile::read_line_string (const gdb_byte *buf,
+                                     unsigned int offset_size)
+{
+  bfd *abfd = objfile->obfd;
+  ULONGEST str_offset = read_offset (abfd, buf, offset_size);
+
+  return per_bfd->line_str.read_string (objfile, str_offset, "DW_FORM_line_strp");
+}
+
+/* See read.h.  */
+
 const char *
 dwarf2_per_objfile::read_line_string (const gdb_byte *buf,
                                      const struct comp_unit_head *cu_header,

diff --git a/gdb/dwarf2/read.h b/gdb/dwarf2/read.h
index 1638d8521c0f176f3a0ecd0ce469a5e5a214e3df..fe34e3f95aedc04fad74fa8161c33334c674631b 100644 (file)
--- a/gdb/dwarf2/read.h
+++ b/gdb/dwarf2/read.h
@@ -517,6 +517,11 @@ struct dwarf2_per_objfile
                                const struct comp_unit_head *cu_header,
                                unsigned int *bytes_read_ptr);
 
+  /* Return pointer to string at .debug_line_str offset as read from BUF.
+     The offset_size is OFFSET_SIZE.  */
+  const char *read_line_string (const gdb_byte *buf,
+                               unsigned int offset_size);
+
   /* Return true if the symtab corresponding to PER_CU has been set,
      false otherwise.  */
   bool symtab_set_p (const dwarf2_per_cu_data *per_cu) const;

diff --git a/gdb/testsuite/gdb.dwarf2/dw2-lines.exp b/gdb/testsuite/gdb.dwarf2/dw2-lines.exp
index 27134af8f5da5fe8a36820b4b011f68837a5755d..9cc24955102e06714fe0a128177ea2640db3b818 100644 (file)
--- a/gdb/testsuite/gdb.dwarf2/dw2-lines.exp
+++ b/gdb/testsuite/gdb.dwarf2/dw2-lines.exp
@@ -37,18 +37,19 @@ proc line_for { l } {
 }
 
 # Execute test.
-proc test_1 { _cv _cdw64 _lv _ldw64 } {
+proc test_1 { _cv _cdw64 _lv _ldw64 {_string_form ""}} {
     global srcfile srcfile2 testfile
-    global cv cdw64 lv ldw64
+    global cv cdw64 lv ldw64 string_form
     set cv $_cv
     set cdw64 $_cdw64
     set lv $_lv
     set ldw64 $_ldw64
+    set string_form $_string_form
 
     set asm_file [standard_output_file $srcfile2]
     Dwarf::assemble $asm_file {
        declare_labels Llines
-       global srcdir subdir srcfile cv cdw64 lv ldw64
+       global srcdir subdir srcfile cv cdw64 lv ldw64 string_form
        global func_info_vars
        foreach var $func_info_vars {
            global $var
@@ -75,7 +76,7 @@ proc test_1 { _cv _cdw64 _lv _ldw64 } {
            }
        }
 
-       lines [list version $lv is_64 $ldw64] Llines {
+       lines [list version $lv is_64 $ldw64 string_form $string_form] Llines {
            include_dir "${srcdir}/${subdir}"
            file_name "$srcfile" 1
 
@@ -121,12 +122,18 @@ proc test_1 { _cv _cdw64 _lv _ldw64 } {
 
 
 # Add unique test prefix.
-proc test { cv cdw64 lv ldw64 } {
+proc test { cv cdw64 lv ldw64 {string_form ""}} {
     with_test_prefix cv=$cv {
        with_test_prefix cdw=[expr $cdw64 ? 64 : 32] {
            with_test_prefix lv=$lv {
                with_test_prefix ldw=[expr $ldw64 ? 64 : 32] {
-                   test_1 $cv $cdw64 $lv $ldw64
+                   if { $string_form == "" } {
+                       test_1 $cv $cdw64 $lv $ldw64
+                   } else {
+                       with_test_prefix string_form=$string_form {
+                           test_1 $cv $cdw64 $lv $ldw64 $string_form
+                       }
+                   }
                }
            }
        }
@@ -157,6 +164,7 @@ for { set cv $cv_low } { $cv <= $cv_high } { incr cv } {
 
 foreach cdw64 { 0 1 } {
     foreach ldw64 { 0 1 } {
-       test 5 $cdw64 5 $ldw64
+       test 5 $cdw64 5 $ldw64 string
+       test 5 $cdw64 5 $ldw64 line_strp
     }
 }

diff --git a/gdb/testsuite/lib/dwarf.exp b/gdb/testsuite/lib/dwarf.exp
index b2a337238c34cafa64fe80d94d9400b368508448..cbb1bf6985aec8928605c53ce7cc243a11f1aeb2 100644 (file)
--- a/gdb/testsuite/lib/dwarf.exp
+++ b/gdb/testsuite/lib/dwarf.exp
@@ -2185,9 +2185,11 @@ namespace eval Dwarf {
        variable _line_saw_program
        variable _line_header_end_label
        variable _line_unit_version
+       variable _line_is_64
+       variable _line_string_form
 
        # Establish the defaults.
-       set is_64 0
+       set _line_is_64 0
        set _line_unit_version 4
        set _unit_addr_size default
        set _line_saw_program 0
@@ -2197,14 +2199,17 @@ namespace eval Dwarf {
        set _line_header_finalized 0
        set _default_is_stmt 1
        set _seg_sel_size 0
+       #set _line_string_form string
+       set _line_string_form line_strp
 
        foreach { name value } $options {
            switch -exact -- $name {
-               is_64 { set is_64 $value }
+               is_64 { set _line_is_64 $value }
                version { set _line_unit_version $value }
                addr_size { set _unit_addr_size $value }
                seg_sel_size { set _seg_sel_size $value }
                default_is_stmt { set _default_is_stmt $value }
+               string_form { set $_line_string_form $value }
                default { error "unknown option $name" }
            }
        }
@@ -2231,7 +2236,7 @@ namespace eval Dwarf {
        set header_len_label [_compute_label "line${_line_count}_header_start"]
        set _line_header_end_label [_compute_label "line${_line_count}_header_end"]
 
-       if {$is_64} {
+       if {$_line_is_64} {
            _op .4byte 0xffffffff
            _op .8byte "$unit_end_label - $unit_len_label" "unit_length"
        } else {
@@ -2248,7 +2253,7 @@ namespace eval Dwarf {
            _op .byte $_seg_sel_size "seg_sel_size"
        }
 
-       if {$is_64} {
+       if {$_line_is_64} {
            _op .8byte "$_line_header_end_label - $header_len_label" "header_length"
        } else {
            _op .4byte "$_line_header_end_label - $header_len_label" "header_length"
@@ -2306,12 +2311,22 @@ namespace eval Dwarf {
            variable _line_file_names
 
            variable _line_unit_version
+           variable _line_is_64
+           variable _line_string_form
            if { $_line_unit_version >= 5 } {
                _op .byte 1 "directory_entry_format_count"
                _op .uleb128 1 \
                    "directory_entry_format (content type code: DW_LNCT_path)"
-               _op .uleb128 0x08 \
-                   "directory_entry_format (form: DW_FORM_string)"
+               switch $_line_string_form {
+                   string {
+                       _op .uleb128 0x08 \
+                           "directory_entry_format (form: DW_FORM_string)"
+                   }
+                   line_strp {
+                       _op .uleb128 0x1f \
+                           "directory_entry_format (form: DW_FORM_line_strp)"
+                   }
+               }
 
                set nr_dirs [llength $_line_include_dirs]
                # For entry 0.
@@ -2324,14 +2339,38 @@ namespace eval Dwarf {
                    [concat [list $dirname] $_line_include_dirs]
 
                foreach dirname $_line_include_dirs {
-                   _op .ascii [_quote $dirname]
+                   switch $_line_string_form {
+                       string {
+                           _op .ascii [_quote $dirname]
+                       }
+                       line_strp {
+                           declare_labels string_ptr
+                           _defer_output .debug_line_str {
+                               string_ptr:
+                               _op .ascii [_quote $dirname]
+                           }
+                           if { $_line_is_64 } {
+                               _op .8byte $string_ptr
+                           } else {
+                               _op .4byte $string_ptr
+                           }
+                       }
+                   }
                }
 
                _op .byte 2 "file_name_entry_format_count"
                _op .uleb128 1 \
                    "file_name_entry_format (content type code: DW_LNCT_path)"
-               _op .uleb128 0x08 \
-                   "file_name_entry_format (form: DW_FORM_string)"
+               switch $_line_string_form {
+                   string {
+                       _op .uleb128 0x08 \
+                           "directory_entry_format (form: DW_FORM_string)"
+                   }
+                   line_strp {
+                       _op .uleb128 0x1f \
+                           "directory_entry_format (form: DW_FORM_line_strp)"
+                   }
+               }
                _op .uleb128 2 \
                    "file_name_entry_format (content type code: DW_LNCT_directory_index)"
                _op .uleb128 0x0f \
@@ -2349,7 +2388,23 @@ namespace eval Dwarf {
                    [concat [list $filename $diridx] $_line_file_names]
 
                foreach { filename diridx } $_line_file_names {
-                   _op .ascii [_quote $filename]
+                   switch $_line_string_form {
+                       string {
+                           _op .ascii [_quote $filename]
+                       }
+                       line_strp {
+                           declare_labels string_ptr
+                           _defer_output .debug_line_str {
+                               string_ptr:
+                               _op .ascii [_quote $filename]
+                           }
+                           if { $_line_is_64 } {
+                               _op .8byte $string_ptr
+                           } else {
+                               _op .4byte $string_ptr
+                           }
+                       }
+                   }
                    _op .uleb128 $diridx
                }
            } else {