350 lines
12 KiB
Diff
350 lines
12 KiB
Diff
Date: Thu, 2 Oct 2014 17:56:53 +0200
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From: Jan Kratochvil <jan dot kratochvil at redhat dot com>
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To: Doug Evans <dje at google dot com>
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Cc: gdb-patches at sourceware dot org
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Subject: [patchv2] Fix 100x slowdown regression on DWZ files
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Message-ID: <20141002155653.GA9001@host2.jankratochvil.net>
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--cNdxnHkX5QqsyA0e
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Content-Type: text/plain; charset=us-ascii
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Content-Disposition: inline
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On Thu, 02 Oct 2014 01:51:38 +0200, Doug Evans wrote:
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> I tested this patch with --target_board=dwarf4-gdb-index
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> and got a failure in m-static.exp:
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That is particularly with -fdebug-types-section.
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> Type units read the line table in a separate path,
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OK, therefore I dropped that separate struct dwarf2_lineinfo
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and reused struct line_header instead.
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> OTOH, I do want to avoid any confusion that this patch may inadvertently
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> introduce. For example, IIUC with your patch as is,
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> if we read a partial_unit first, before a compile_unit
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> that has the same stmt_list value, we'll do more processing in
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> dwarf_decode_lines than we really need to since we only need a file
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> number to symtab mapping. And if we later read in a compile_unit
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> with the same stmt_value we'll call dwarf_decode_lines again,
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> and this time we need the pc/line mapping it computes.
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> Whereas if we process these in the opposite order we'll only call
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> dwarf_decode_lines once. I'm sure this will be confusing at first
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> to some later developer going through this code.
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> [I could be missing something of course, and I'm happy for any corrections.]
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Implemented (omitting some story why I did not include it before).
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> The code that processes stmt_list for type_units is in setup_type_unit_groups.
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> Note that this code goes to the trouble of re-initializing the buildsym
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> machinery (see the calls to restart_symtab in dwarf2read.c) when we process
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> the second and subsequent type units that share a stmt_list value.
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> This is something that used to be done before your patch and will no
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> longer be done with your patch (since if we get a cache hit we exit).
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> It may be that the type_unit support is doing this unnecessarily,
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> which would be great because we can then simplify it.
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I hope this patch should no longer break -fdebug-types-section.
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If it additionally enables some future optimization for -fdebug-types-section
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the better.
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> > + /* Offset of line number information in .debug_line section. */
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> > + sect_offset offset;
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> > + unsigned offset_in_dwz : 1;
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>
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> IWBN to document why offset_in_dwz is here.
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> It's not obvious why it's needed.
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+
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On Thu, 02 Oct 2014 01:57:03 +0200, Doug Evans wrote:
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> Ah, I guess the offset_in_dwz flag will ensure dwarf_decode_lines gets called
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> twice regardless of order. But is that the only reason for the flag?
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I have added there now:
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+ /* OFFSET is for struct dwz_file associated with dwarf2_per_objfile. */
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If one removes it regressions really happen. What happens is that this
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line_header_hash (former lineinfo_hash) is in struct dwarf2_per_objfile which
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is common for both objfile and its objfile.dwz (that one is normally in
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/usr/lib/debug/.dwz/ - common for multiple objfiles). And there are two
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different DIEs at offset 0xb - one in objfile and one in objfile.dwz - which
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would match single line_header if offset_in_dwz was not there.
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Also existing dwarf2read.c code usually transfers "dwz flag" together with DIE
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offset, such as:
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dwarf2_find_containing_comp_unit (sect_offset offset,
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unsigned int offset_in_dwz,
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struct objfile *objfile)
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This reminds me - why doesn't similar ambiguity happen also for dwp_file?
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I am unfortunately not much aware of the dwp implementation details.
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> > - struct line_header *line_header
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> > - = dwarf_decode_line_header (line_offset, cu);
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> > + dwarf2_per_objfile->lineinfo_hash =
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>
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> As much as I prefer "=" going here, convention says to put it on the
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> next line.
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I have changed it but this was just blind copy from existing line 21818.
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> > + htab_create_alloc_ex (127, dwarf2_lineinfo_hash, dwarf2_lineinfo_eq,
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>
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> I don't have any data, but 127 seems high.
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I have not changed it but this was just blind copy from existing line 21818.
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> I wouldn't change it, I just wanted to ask if you have any data
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> guiding this choice.
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Tuning some constants really makes no sense when GDB has missing + insanely
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complicated data structures and in consequence GDB is using inappropriate data
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structures with bad algorithmic complexity. One needs to switch GDB to C++
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and its STL before one can start talking about data structures performance.
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No regressions on {x86_64,x86_64-m32,i686}-fedora20-linux-gnu in DWZ mode and
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in -fdebug-types-section mode.
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Thanks,
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Jan
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--cNdxnHkX5QqsyA0e
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Content-Type: text/plain; charset=us-ascii
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Content-Disposition: inline; filename="partialunit5.patch"
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gdb/
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2014-10-02 Jan Kratochvil <jan.kratochvil@redhat.com>
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Fix 100x slowdown regression on DWZ files.
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* dwarf2read.c (struct dwarf2_per_objfile): Add line_header_hash.
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(struct line_header): Add offset and offset_in_dwz.
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(dwarf_decode_lines): Add parameter decode_mapping to the declaration.
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(free_line_header_voidp): New declaration.
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(line_header_hash, line_header_eq): New functions.
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(dwarf2_build_include_psymtabs): Update dwarf_decode_lines caller.
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(handle_DW_AT_stmt_list): Use dwarf2_per_objfile->line_header_hash.
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(free_line_header_voidp): New function.
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(dwarf_decode_line_header): Initialize offset and offset_in_dwz.
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(dwarf_decode_lines): New parameter decode_mapping, use it.
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Index: gdb-7.8.50.20141228/gdb/dwarf2read.c
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===================================================================
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--- gdb-7.8.50.20141228.orig/gdb/dwarf2read.c 2015-01-05 22:45:32.823240453 +0100
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+++ gdb-7.8.50.20141228/gdb/dwarf2read.c 2015-01-05 22:49:35.270332647 +0100
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@@ -309,6 +309,9 @@ struct dwarf2_per_objfile
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/* The CUs we recently read. */
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VEC (dwarf2_per_cu_ptr) *just_read_cus;
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+
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+ /* Table containing line_header indexed by offset and offset_in_dwz. */
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+ htab_t line_header_hash;
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};
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static struct dwarf2_per_objfile *dwarf2_per_objfile;
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@@ -1025,6 +1028,12 @@ typedef void (die_reader_func_ftype) (co
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which contains the following information. */
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struct line_header
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{
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+ /* Offset of line number information in .debug_line section. */
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+ sect_offset offset;
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+
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+ /* OFFSET is for struct dwz_file associated with dwarf2_per_objfile. */
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+ unsigned offset_in_dwz : 1;
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+
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unsigned int total_length;
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unsigned short version;
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unsigned int header_length;
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@@ -1513,7 +1522,7 @@ static struct line_header *dwarf_decode_
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static void dwarf_decode_lines (struct line_header *, const char *,
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struct dwarf2_cu *, struct partial_symtab *,
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- CORE_ADDR);
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+ CORE_ADDR, int decode_mapping);
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static void dwarf2_start_subfile (const char *, const char *);
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@@ -2057,6 +2066,8 @@ get_section_file_name (const struct dwar
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/* Return the id of SECTION.
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Returns 0 if SECTION doesn't exist. */
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+static void free_line_header_voidp (void *arg);
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+
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static int
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get_section_id (const struct dwarf2_section_info *section)
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{
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@@ -2461,6 +2472,29 @@ dwarf2_get_dwz_file (void)
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dwarf2_per_objfile->dwz_file = result;
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return result;
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}
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+
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+/* Hash function for line_header_hash. */
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+
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+static hashval_t
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+line_header_hash (const void *item)
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+{
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+ const struct line_header *ofs = item;
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+
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+ return ofs->offset.sect_off ^ ofs->offset_in_dwz;
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+}
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+
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+/* Equality function for line_header_hash. */
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+
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+static int
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+line_header_eq (const void *item_lhs, const void *item_rhs)
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+{
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+ const struct line_header *ofs_lhs = item_lhs;
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+ const struct line_header *ofs_rhs = item_rhs;
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+
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+ return (ofs_lhs->offset.sect_off == ofs_rhs->offset.sect_off
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+ && ofs_lhs->offset_in_dwz == ofs_rhs->offset_in_dwz);
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+}
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+
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/* DWARF quick_symbols_functions support. */
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@@ -4454,7 +4488,7 @@ dwarf2_build_include_psymtabs (struct dw
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return; /* No linetable, so no includes. */
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/* NOTE: pst->dirname is DW_AT_comp_dir (if present). */
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- dwarf_decode_lines (lh, pst->dirname, cu, pst, pst->textlow);
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+ dwarf_decode_lines (lh, pst->dirname, cu, pst, pst->textlow, 1);
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free_line_header (lh);
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}
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@@ -9002,24 +9036,64 @@ static void
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handle_DW_AT_stmt_list (struct die_info *die, struct dwarf2_cu *cu,
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const char *comp_dir, CORE_ADDR lowpc) /* ARI: editCase function */
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{
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+ struct objfile *objfile = dwarf2_per_objfile->objfile;
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struct attribute *attr;
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+ unsigned int line_offset;
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+ struct line_header *line_header, line_header_local;
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+ unsigned u;
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+ void **slot;
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+ int decode_mapping;
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gdb_assert (! cu->per_cu->is_debug_types);
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attr = dwarf2_attr (die, DW_AT_stmt_list, cu);
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- if (attr)
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+ if (attr == NULL)
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+ return;
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+
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+ line_offset = DW_UNSND (attr);
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+
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+ if (dwarf2_per_objfile->line_header_hash == NULL)
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{
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- unsigned int line_offset = DW_UNSND (attr);
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- struct line_header *line_header
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- = dwarf_decode_line_header (line_offset, cu);
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-
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- if (line_header)
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- {
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- cu->line_header = line_header;
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- make_cleanup (free_cu_line_header, cu);
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- dwarf_decode_lines (line_header, comp_dir, cu, NULL, lowpc);
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- }
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+ dwarf2_per_objfile->line_header_hash
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+ = htab_create_alloc_ex (127, line_header_hash, line_header_eq,
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+ free_line_header_voidp,
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+ &objfile->objfile_obstack,
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+ hashtab_obstack_allocate,
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+ dummy_obstack_deallocate);
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+ }
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+
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+ line_header_local.offset.sect_off = line_offset;
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+ line_header_local.offset_in_dwz = cu->per_cu->is_dwz;
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+ slot = htab_find_slot (dwarf2_per_objfile->line_header_hash,
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+ &line_header_local, NO_INSERT);
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+
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+ /* For DW_TAG_compile_unit we need info like symtab::linetable which
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+ is not present in *SLOT. */
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+ if (die->tag == DW_TAG_partial_unit && slot != NULL)
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+ {
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+ gdb_assert (*slot != NULL);
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+ cu->line_header = *slot;
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+ return;
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+ }
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+
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+ line_header = dwarf_decode_line_header (line_offset, cu);
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+ if (line_header == NULL)
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+ return;
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+ cu->line_header = line_header;
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+
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+ slot = htab_find_slot (dwarf2_per_objfile->line_header_hash,
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+ &line_header_local, INSERT);
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+ gdb_assert (slot != NULL);
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+ if (*slot == NULL)
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+ *slot = line_header;
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+ else
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+ {
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+ gdb_assert (die->tag != DW_TAG_partial_unit);
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+ make_cleanup (free_cu_line_header, cu);
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}
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+ decode_mapping = (die->tag != DW_TAG_partial_unit);
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+ dwarf_decode_lines (line_header, comp_dir, cu, NULL, lowpc,
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+ decode_mapping);
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}
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/* Process DW_TAG_compile_unit or DW_TAG_partial_unit. */
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@@ -16917,6 +16991,16 @@ free_line_header (struct line_header *lh
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xfree (lh);
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}
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+/* Stub for free_line_header to match void * callback types. */
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+
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+static void
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+free_line_header_voidp (void *arg)
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+{
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+ struct line_header *lh = arg;
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+
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+ free_line_header (lh);
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+}
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+
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/* Add an entry to LH's include directory table. */
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static void
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@@ -17047,6 +17131,9 @@ dwarf_decode_line_header (unsigned int o
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back_to = make_cleanup ((make_cleanup_ftype *) free_line_header,
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(void *) lh);
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+ lh->offset.sect_off = offset;
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+ lh->offset_in_dwz = cu->per_cu->is_dwz;
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+
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line_ptr = section->buffer + offset;
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/* Read in the header. */
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@@ -17674,17 +17761,22 @@ dwarf_decode_lines_1 (struct line_header
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E.g. expand_line_sal requires this when finding psymtabs to expand.
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A good testcase for this is mb-inline.exp.
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- LOWPC is the lowest address in CU (or 0 if not known). */
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+ LOWPC is the lowest address in CU (or 0 if not known).
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+
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+ Boolean DECODE_MAPPING specifies we need to fully decode .debug_line
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+ for its PC<->lines mapping information. Otherwise only filenames
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+ tables is read in. */
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static void
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dwarf_decode_lines (struct line_header *lh, const char *comp_dir,
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struct dwarf2_cu *cu, struct partial_symtab *pst,
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- CORE_ADDR lowpc)
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+ CORE_ADDR lowpc, int decode_mapping)
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{
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struct objfile *objfile = cu->objfile;
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const int decode_for_pst_p = (pst != NULL);
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- dwarf_decode_lines_1 (lh, cu, decode_for_pst_p, lowpc);
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+ if (decode_mapping)
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+ dwarf_decode_lines_1 (lh, cu, decode_for_pst_p, lowpc);
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if (decode_for_pst_p)
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{
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