https://sourceware.org/bugzilla/show_bug.cgi?id=28233
Bug ID: 28233
Summary: [gas, --gstabs] Generate stabs more similar to gcc
Product: binutils
Version: unspecified
Status: NEW
Severity: normal
Priority: P2
Component: gas
Assignee: unassigned at sourceware dot org
Reporter: vries at gcc dot gnu.org
Target Milestone: ---
Consider test-case ./src/gdb/testsuite/gdb.dwarf2/dw2-ranges-3.c.
When compiled with gcc -gstabs:
...
$ gcc -gstabs -c -fno-PIE -no-pie -o dw2-ranges3.o
./src/gdb/testsuite/gdb.dwarf2/dw2-ranges-3.c
...
we have (using objdump -G, filtering out LSYM entries 2-26 for brevity):
...
Contents of .stab section:
Symnum n_type n_othr n_desc n_value n_strx String
-1 HdrSym 0 31 00000000000003ab 1
0 SO 0 2 0000000000000000 16
./src/gdb/testsuite/gdb.dwarf2/dw2-ranges-3.c
1 OPT 0 0 0000000000000000 62 gcc2_compiled.
...
27 FUN 0 0 0000000000000000 925 main3:F(0,25)
28 SLINE 0 19 0000000000000000 0
29 SLINE 0 20 0000000000000004 0
30 SO 0 0 0000000000000000 0
$
...
Now consider generating stabs using gas --gstabs instead:
...
$ gcc -c -fno-PIE -no-pie -o dw2-ranges3.o
./src/gdb/testsuite/gdb.dwarf2/dw2-ranges-3.c -Wa,--gstabs
...
Instead we have:
...
Contents of .stab section:
Symnum n_type n_othr n_desc n_value n_strx String
-1 HdrSym 0 6 0000000000000021 1
0 SO 0 0 0000000000000000 17 /tmp/ccO3O0w5.s
1 SLINE 0 8 0000000000000000 0
2 SLINE 0 11 0000000000000000 0
3 SLINE 0 13 0000000000000000 0
4 SLINE 0 14 0000000000000000 0
5 SLINE 0 16 0000000000000000 0
...
There are two differences (not counting the OPT entry) in the generated
entries:
- no FUN entry
- no terminating SO entry
I don't know enough about stabs to say whether this is valid or not (and if
not, if it's caused by a problem with the input).
What I do know is that these two differences trigger two different problems in
gdb:
- the FUN entry is required to support stabs+PIE (PR12497)
- terminating SO entry is required to get a correct address table (PR28221)
I've submitted a patch for the first PR, but reaction was not positive. So I
wonder, perhaps it's a good idea to make gas generate stabs more similar to
what gcc emits.
The missing FUN entry problem can be fixed by manually adding a .func
directive. I've wondered whether we could get the same effect by interpreting
".type main3, @function" which is present in the generated .s file.
I've found no similar workaround for the missing SO entry problem, so I wrote a
patch for this.
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