From: Bob Wilson <bwilson@tensilica.com>
To: binutils@sources.redhat.com
Subject: Re: DWARF updates for linker relaxation?
Date: Fri, 28 Jul 2006 23:28:00 -0000 [thread overview]
Message-ID: <44CA9D81.7000201@tensilica.com> (raw)
In-Reply-To: <44BC01FE.1010303@tensilica.com>
[-- Attachment #1: Type: text/plain, Size: 1515 bytes --]
On Mon, 17 Jul 2006 at 14:32:46 -0700, Bob Wilson wrote:
> How do I make this work? It seems like the obvious approach is to have a hook
> in the assembler to make it use the generic "advance_pc" opcode instead of
> "special opcodes", with relocations on the address offset fields. The SH code
> mentioned above made me think there might already be code for this somewhere
> in the assembler, but I haven't found it.
>
> Any suggestions?
I didn't get any suggestions or pointers to existing code, so I came up with my
own solution for this. It allows a port to specify that DWARF line numbers
should be specified using the DW_LNS_fixed_advance_pc opcodes. This allows
linker relaxation to update the PC offsets, at the expense of slightly larger
.debug_line sections.
I tested this by building for both i686-pc-linux-gnu and xtensa-elf targets.
The testsuite passes with no regressions, except for one. For the xtensa-elf
target, the lns/lns-common-1 test fails because the expected dump file no longer
matches. Is there an easy way to specify an alternate expected dump file?
Otherwise, I guess I could skip this test for Xtensa targets.
Assuming I get that regression fixed, is this OK?
2006-07-28 Bob Wilson <bob.wilson@acm.org>
* dwarf2dbg.c (DWARF2_USE_FIXED_ADVANCE_PC): New.
(out_sleb128): New.
(out_fixed_inc_line_addr): New.
(process_entries): Use out_fixed_inc_line_addr when
DWARF2_USE_FIXED_ADVANCE_PC is set.
* config/tc-xtensa.h (DWARF2_USE_FIXED_ADVANCE_PC): Define.
[-- Attachment #2: dwarf-linkrelax.diff --]
[-- Type: text/plain, Size: 4662 bytes --]
Index: dwarf2dbg.c
===================================================================
RCS file: /cvs/src/src/gas/dwarf2dbg.c,v
retrieving revision 1.85
diff -u -p -r1.85 dwarf2dbg.c
--- dwarf2dbg.c 7 Jun 2006 11:27:57 -0000 1.85
+++ dwarf2dbg.c 28 Jul 2006 22:57:04 -0000
@@ -88,6 +88,13 @@
#define DL_FILES 1
#define DL_BODY 2
+/* If linker relaxation might change offsets in the code, the DWARF special
+ opcodes and variable-length operands cannot be used. If this macro is
+ nonzero, use the DW_LNS_fixed_advance_pc opcode instead. */
+#ifndef DWARF2_USE_FIXED_ADVANCE_PC
+# define DWARF2_USE_FIXED_ADVANCE_PC 0
+#endif
+
/* First special line opcde - leave room for the standard opcodes.
Note: If you want to change this, you'll have to update the
"standard_opcode_lengths" table that is emitted below in
@@ -191,11 +198,13 @@ static void out_two (int);
static void out_four (int);
static void out_abbrev (int, int);
static void out_uleb128 (addressT);
+static void out_sleb128 (addressT);
static offsetT get_frag_fix (fragS *, segT);
static void out_set_addr (symbolS *);
static int size_inc_line_addr (int, addressT);
static void emit_inc_line_addr (int, addressT, char *, int);
static void out_inc_line_addr (int, addressT);
+static void out_fixed_inc_line_addr (int, symbolS *, symbolS *);
static void relax_inc_line_addr (int, symbolS *, symbolS *);
static void process_entries (segT, struct line_entry *);
static void out_file_list (void);
@@ -746,6 +755,14 @@ out_uleb128 (addressT value)
output_leb128 (frag_more (sizeof_leb128 (value, 0)), value, 0);
}
+/* Emit a signed "little-endian base 128" number. */
+
+static void
+out_sleb128 (addressT value)
+{
+ output_leb128 (frag_more (sizeof_leb128 (value, 1)), value, 1);
+}
+
/* Emit a tuple for .debug_abbrev. */
static inline void
@@ -979,6 +996,45 @@ out_inc_line_addr (int line_delta, addre
emit_inc_line_addr (line_delta, addr_delta, frag_more (len), len);
}
+/* Write out an alternative form of line and address skips using
+ DW_LNS_fixed_advance_pc opcodes. This uses more space than the default
+ line and address information, but it helps support linker relaxation that
+ changes the code offsets. */
+
+static void
+out_fixed_inc_line_addr (int line_delta, symbolS *to_sym, symbolS *from_sym)
+{
+ expressionS expr;
+
+ /* INT_MAX is a signal that this is actually a DW_LNE_end_sequence. */
+ if (line_delta == INT_MAX)
+ {
+ out_opcode (DW_LNS_fixed_advance_pc);
+ expr.X_op = O_subtract;
+ expr.X_add_symbol = to_sym;
+ expr.X_op_symbol = from_sym;
+ expr.X_add_number = 0;
+ emit_expr (&expr, 2);
+
+ out_opcode (DW_LNS_extended_op);
+ out_byte (1);
+ out_opcode (DW_LNE_end_sequence);
+ return;
+ }
+
+ out_opcode (DW_LNS_advance_line);
+ out_sleb128 (line_delta);
+
+ out_opcode (DW_LNS_fixed_advance_pc);
+ expr.X_op = O_subtract;
+ expr.X_add_symbol = to_sym;
+ expr.X_op_symbol = from_sym;
+ expr.X_add_number = 0;
+ emit_expr (&expr, 2);
+
+ out_opcode (DW_LNS_copy);
+}
+
/* Generate a variant frag that we can use to relax address/line
increments between fragments of the target segment. */
@@ -1129,6 +1185,8 @@ process_entries (segT seg, struct line_e
out_set_addr (lab);
out_inc_line_addr (line_delta, 0);
}
+ else if (DWARF2_USE_FIXED_ADVANCE_PC)
+ out_fixed_inc_line_addr (line_delta, lab, last_lab);
else if (frag == last_frag)
out_inc_line_addr (line_delta, frag_ofs - last_frag_ofs);
else
@@ -1148,7 +1206,12 @@ process_entries (segT seg, struct line_e
/* Emit a DW_LNE_end_sequence for the end of the section. */
frag = last_frag_for_seg (seg);
frag_ofs = get_frag_fix (frag, seg);
- if (frag == last_frag)
+ if (DWARF2_USE_FIXED_ADVANCE_PC)
+ {
+ lab = symbol_temp_new (seg, frag_ofs, frag);
+ out_fixed_inc_line_addr (INT_MAX, lab, last_lab);
+ }
+ else if (frag == last_frag)
out_inc_line_addr (INT_MAX, frag_ofs - last_frag_ofs);
else
{
Index: config/tc-xtensa.h
===================================================================
RCS file: /cvs/src/src/gas/config/tc-xtensa.h,v
retrieving revision 1.19
diff -u -p -r1.19 tc-xtensa.h
--- config/tc-xtensa.h 31 Jan 2006 19:36:57 -0000 1.19
+++ config/tc-xtensa.h 28 Jul 2006 22:57:05 -0000
@@ -371,6 +371,9 @@ extern char *xtensa_section_rename (char
#define MD_APPLY_SYM_VALUE(FIX) 0
#define SUB_SEGMENT_ALIGN(SEG, FRCHAIN) 0
+/* Use line number format that is amenable to linker relaxation. */
+#define DWARF2_USE_FIXED_ADVANCE_PC (linkrelax != 0)
+
/* Resource reservation info functions. */
next prev parent reply other threads:[~2006-07-28 23:28 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-07-17 21:32 Bob Wilson
2006-07-28 23:28 ` Bob Wilson [this message]
2006-08-08 10:16 ` Nick Clifton
2006-08-09 0:12 ` Bob Wilson
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=44CA9D81.7000201@tensilica.com \
--to=bwilson@tensilica.com \
--cc=binutils@sources.redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).