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gas: Don't use frag_align but use plain padding to align .debug_aranges. 

out_debug_aranges uses frag_align to make sure the addresses start
out aligned. Using frag_align will call frag_var[_init], which will
end up calling TC_FRAG_INIT. On arm and aarch64 TC_FRAG_INIT will
generate a $d mapping symbol for the .debug_aranges to show that at
that point a sequence of data items starts.

Such a symbol pointing into a non-allocated debug section will confuse
eu-strip -g. And it seems inefficient and wrong in general to have
additional mapping symbols for debug sections, which won't contain
actual code in the first place.

Just keep track of the aranges header size and use plain padding to
align the addresses which avoids generating any mapping symbols on
aarch64 and arm.

Includes a testcase for aarch64 that PASS with this patch and shows
the extra $d mapping symbol in .debug_aranges before.

gas/ChangeLog

       * dwarf2dbg.c (out_header): Document EXPR->X_add_number value,
       out_debug_aranges depends on it.
       (out_debug_aranges): Track size of header to properly pad header
       for address alignment.

gas/testsuite/ChangeLog

       * gas/aarch64/dwarf.d: New.
       * gas/aarch64/dwarf.s: New.
This commit is contained in:
Mark Wielaard 2015-06-13 17:47:41 -04:00
parent 3a062fa1ee
commit d025d5e5b5
5 changed files with 55 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
gas/ChangeLog
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@ -1,3 +1,10 @@
2015-06-13 Mark Wielaard <mjw@redhat.com>
* dwarf2dbg.c (out_header): Document EXPR->X_add_number value,
out_debug_aranges depends on it.
(out_debug_aranges): Track size of header to properly pad header
for address alignment.
2015-06-11 John David Anglin <danglin@gcc.gnu.org>
PR gas/18427

12
gas/dwarf2dbg.c
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@ -1458,7 +1458,8 @@ out_file_list (void)
/* Switch to SEC and output a header length field. Return the size of
offsets used in SEC. The caller must set EXPR->X_add_symbol value
to the end of the section. */
to the end of the section. EXPR->X_add_number will be set to the
negative size of the header. */
static int
out_header (asection *sec, expressionS *exp)
@ -1638,6 +1639,7 @@ static void
out_debug_aranges (segT aranges_seg, segT info_seg)
{
unsigned int addr_size = sizeof_address;
offsetT size;
struct line_seg *s;
expressionS exp;
symbolS *aranges_end;
@ -1646,21 +1648,27 @@ out_debug_aranges (segT aranges_seg, segT info_seg)
sizeof_offset = out_header (aranges_seg, &exp);
aranges_end = exp.X_add_symbol;
size = -exp.X_add_number;
/* Version. */
out_two (DWARF2_ARANGES_VERSION);
size += 2;
/* Offset to .debug_info. */
TC_DWARF2_EMIT_OFFSET (section_symbol (info_seg), sizeof_offset);
size += sizeof_offset;
/* Size of an address (offset portion). */
out_byte (addr_size);
size++;
/* Size of a segment descriptor. */
out_byte (0);
size++;
/* Align the header. */
frag_align (ffs (2 * addr_size) - 1, 0, 0);
while ((size++ % (2 * addr_size)) > 0)
out_byte (0);
for (s = all_segs; s; s = s->next)
{

5
gas/testsuite/ChangeLog
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@ -1,3 +1,8 @@
2015-06-13 Mark Wielaard <mjw@redhat.com>
* gas/aarch64/dwarf.d: New.
* gas/aarch64/dwarf.s: New.
2015-06-03 Matthew Wahab <matthew.wahab@arm.com>
* gas/arm/armv8-a+rdma.d: New.

27
gas/testsuite/gas/aarch64/dwarf.d Normal file
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@ -0,0 +1,27 @@
#readelf: -s --debug-dump=aranges
#as: -g
Symbol table '.symtab' contains 10 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND
1: 0000000000000000 0 SECTION LOCAL DEFAULT 1
2: 0000000000000000 0 SECTION LOCAL DEFAULT 2
3: 0000000000000000 0 SECTION LOCAL DEFAULT 3
4: 0000000000000000 0 NOTYPE LOCAL DEFAULT 1 \$x
5: 0000000000000000 0 SECTION LOCAL DEFAULT 6
6: 0000000000000000 0 SECTION LOCAL DEFAULT 8
7: 0000000000000000 0 SECTION LOCAL DEFAULT 4
8: 0000000000000000 0 SECTION LOCAL DEFAULT 9
9: 0000000000000000 8 FUNC GLOBAL DEFAULT 1 testfunc
Contents of the .debug_aranges section:
Length: 44
Version: 2
Offset into .debug_info: 0x0
Pointer Size: 8
Segment Size: 0
Address Length
0000000000000000 0000000000000008
0000000000000000 0000000000000000

6
gas/testsuite/gas/aarch64/dwarf.s Normal file
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@ -0,0 +1,6 @@
.globl testfunc
testfunc:
nop
ret
.type testfunc, @function
.size testfunc, .-testfunc