1cdfc98a99
On the testcase in the PR with
-fno-tree-sink -O3 -fPIC -fomit-frame-pointer -fno-strict-aliasing -mstackrealign
we have prologue:
0000000000000000 <_func_with_dwarf_issue_>:
0: 4c 8d 54 24 08 lea 0x8(%rsp),%r10
5: 48 83 e4 f0 and $0xfffffffffffffff0,%rsp
9: 41 ff 72 f8 pushq -0x8(%r10)
d: 55 push %rbp
e: 48 89 e5 mov %rsp,%rbp
11: 41 57 push %r15
13: 41 56 push %r14
15: 41 55 push %r13
17: 41 54 push %r12
19: 41 52 push %r10
1b: 53 push %rbx
1c: 48 83 ec 20 sub $0x20,%rsp
and emit
00000000 0000000000000014 00000000 CIE
Version: 1
Augmentation: "zR"
Code alignment factor: 1
Data alignment factor: -8
Return address column: 16
Augmentation data: 1b
DW_CFA_def_cfa: r7 (rsp) ofs 8
DW_CFA_offset: r16 (rip) at cfa-8
DW_CFA_nop
DW_CFA_nop
00000018 0000000000000044 0000001c FDE cie=00000000 pc=0000000000000000..00000000000001d5
DW_CFA_advance_loc: 5 to 0000000000000005
DW_CFA_def_cfa: r10 (r10) ofs 0
DW_CFA_advance_loc: 9 to 000000000000000e
DW_CFA_expression: r6 (rbp) (DW_OP_breg6 (rbp): 0)
DW_CFA_advance_loc: 13 to 000000000000001b
DW_CFA_def_cfa_expression (DW_OP_breg6 (rbp): -40; DW_OP_deref)
DW_CFA_expression: r15 (r15) (DW_OP_breg6 (rbp): -8)
DW_CFA_expression: r14 (r14) (DW_OP_breg6 (rbp): -16)
DW_CFA_expression: r13 (r13) (DW_OP_breg6 (rbp): -24)
DW_CFA_expression: r12 (r12) (DW_OP_breg6 (rbp): -32)
...
unwind info for that. The problem is when async signal
(or stepping through in the debugger) stops after the pushq %rbp
instruction and before movq %rsp, %rbp, the unwind info says that
caller's %rbp is saved there at *%rbp, but that is not true, caller's
%rbp is either still available in the %rbp register, or in *%rsp,
only after executing the next instruction - movq %rsp, %rbp - the
location for %rbp is correct. So, either we'd need to temporarily
say:
DW_CFA_advance_loc: 9 to 000000000000000e
DW_CFA_expression: r6 (rbp) (DW_OP_breg7 (rsp): 0)
DW_CFA_advance_loc: 3 to 0000000000000011
DW_CFA_expression: r6 (rbp) (DW_OP_breg6 (rbp): 0)
DW_CFA_advance_loc: 10 to 000000000000001b
or to me it seems more compact to just say:
DW_CFA_advance_loc: 12 to 0000000000000011
DW_CFA_expression: r6 (rbp) (DW_OP_breg6 (rbp): 0)
DW_CFA_advance_loc: 10 to 000000000000001b
I've tried instead to deal with it through REG_FRAME_RELATED_EXPR
from the backend, but that failed miserably as explained in the PR,
dwarf2cfi.c has some rules (Rule 16 to Rule 19) that are specific to the
dynamic stack realignment using drap register that only the i386 backend
does right now, and by using REG_FRAME_RELATED_EXPR or REG_CFA* notes we
can't emulate those rules. The following patch instead does the deferring
of the hard frame pointer save rule in dwarf2cfi.c Rule 18 handling and
emits it on the (set hfp sp) assignment that must appear shortly after it
and adds assertion that it is the case.
The difference before/after the patch on the assembly is:
--- pr99334.s~ 2021-03-26 15:42:40.881749380 +0100
+++ pr99334.s 2021-03-26 17:38:05.729161910 +0100
@@ -11,8 +11,8 @@ _func_with_dwarf_issue_:
andq $-16, %rsp
pushq -8(%r10)
pushq %rbp
- .cfi_escape 0x10,0x6,0x2,0x76,0
movq %rsp, %rbp
+ .cfi_escape 0x10,0x6,0x2,0x76,0
pushq %r15
pushq %r14
pushq %r13
i.e. does just what we IMHO need, after pushq %rbp %rbp
still contains parent's frame value and so the save rule doesn't
need to be overridden there, ditto at the start of the next insn
before the side-effect took effect, and we override it only after
it when %rbp already has the right value.
If some other target adds dynamic stack realignment in the future and
the offset 0 case wouldn't be true there, the code can be adjusted so that
it works on all the drap architectures, I'm pretty sure the code would
need other adjustments too.
For the rule 18 and for the (set hfp sp) after it we already have asserts
for the drap cases that check whether the code looks the way i?86/x86_64
emit it currently.
2021-03-26 Jakub Jelinek <jakub@redhat.com>
PR debug/99334
* dwarf2out.h (struct dw_fde_node): Add rule18 member.
* dwarf2cfi.c (dwarf2out_frame_debug_expr): When handling (set hfp sp)
assignment with drap_reg active, queue reg save for hfp with offset 0
and flush queued reg saves. When handling a push with rule18,
defer queueing reg save for hfp and just assert the offset is 0.
(scan_trace): Assert that fde->rule18 is false.
|
||
|---|---|---|
| c++tools | ||
| config | ||
| contrib | ||
| fixincludes | ||
| gcc | ||
| gnattools | ||
| gotools | ||
| include | ||
| INSTALL | ||
| intl | ||
| libada | ||
| libatomic | ||
| libbacktrace | ||
| libcc1 | ||
| libcody | ||
| libcpp | ||
| libdecnumber | ||
| libffi | ||
| libgcc | ||
| libgfortran | ||
| libgo | ||
| libgomp | ||
| libhsail-rt | ||
| libiberty | ||
| libitm | ||
| libobjc | ||
| liboffloadmic | ||
| libphobos | ||
| libquadmath | ||
| libsanitizer | ||
| libssp | ||
| libstdc++-v3 | ||
| libvtv | ||
| lto-plugin | ||
| maintainer-scripts | ||
| zlib | ||
| .dir-locals.el | ||
| .gitattributes | ||
| .gitignore | ||
| ABOUT-NLS | ||
| ar-lib | ||
| ChangeLog | ||
| ChangeLog.jit | ||
| ChangeLog.tree-ssa | ||
| compile | ||
| config-ml.in | ||
| config.guess | ||
| config.rpath | ||
| config.sub | ||
| configure | ||
| configure.ac | ||
| COPYING | ||
| COPYING3 | ||
| COPYING3.LIB | ||
| COPYING.LIB | ||
| COPYING.RUNTIME | ||
| depcomp | ||
| install-sh | ||
| libtool-ldflags | ||
| libtool.m4 | ||
| lt~obsolete.m4 | ||
| ltgcc.m4 | ||
| ltmain.sh | ||
| ltoptions.m4 | ||
| ltsugar.m4 | ||
| ltversion.m4 | ||
| MAINTAINERS | ||
| Makefile.def | ||
| Makefile.in | ||
| Makefile.tpl | ||
| missing | ||
| mkdep | ||
| mkinstalldirs | ||
| move-if-change | ||
| multilib.am | ||
| README | ||
| symlink-tree | ||
| test-driver | ||
| ylwrap | ||
This directory contains the GNU Compiler Collection (GCC). The GNU Compiler Collection is free software. See the files whose names start with COPYING for copying permission. The manuals, and some of the runtime libraries, are under different terms; see the individual source files for details. The directory INSTALL contains copies of the installation information as HTML and plain text. The source of this information is gcc/doc/install.texi. The installation information includes details of what is included in the GCC sources and what files GCC installs. See the file gcc/doc/gcc.texi (together with other files that it includes) for usage and porting information. An online readable version of the manual is in the files gcc/doc/gcc.info*. See http://gcc.gnu.org/bugs/ for how to report bugs usefully. Copyright years on GCC source files may be listed using range notation, e.g., 1987-2012, indicating that every year in the range, inclusive, is a copyrightable year that could otherwise be listed individually.