https://llvm.org/bugs/show_bug.cgi?id=26844
Bug ID: 26844
Summary: clang 3.8.0/powerpc C++ exception .eh_frame ABI
violation/incompleteness leads to SEGV
Product: clang
Version: 3.8
Hardware: PC
OS: FreeBSD
Status: NEW
Severity: normal
Priority: P
Component: C++
Assignee: unassignedclangb...@nondot.org
Reporter: mar...@dsl-only.net
CC: dgre...@apple.com, llvm-bugs@lists.llvm.org
Classification: Unclassified
[This is for FreeBSD's projects/clang380-import-r296011 at the time of
submittal.]
In the normal C++ ABI exception handling uses 4 scratch registers: "These
scratch registers are reserved for passing arguments between the personality
routine and the landing pads". This is for "an unwind context representing a
handler frame, for which the personality routine will return
_URC_INSTALL_CONTEXT" (_Unwind_SetGR).
Prior to executing in the landing pad the context record is used to restore
various registers "to their state in the frame before the call that threw that
exception": callee-saved (not altered by the personality routine) and scratch.
For TARGET_ARCH=powerpc (or powerpc64) FreeBSD's system libgcc_s
_Unwind_RaiseException gets differing behavior for this between gcc/g++ and
clang/clang++ for the scratch registers (and more):
A) gcc/g++ uses the 4 registers r3, r4, r5, r6 as the scratch registers and
sets up to save/restore them, doing so being reported on by the .eh_frame
information for _Unwind_RaiseException. It also sets up to save/restore R14-r31
and floating point registers as r46-r63. It also sets up to save/restore "r70"
(holding the value from mfcr). (The powerpc ABI uses a bit in the cr for
floating point usage information in the call standard.)
B) clang/clang++ does not set up to save/restore any scratch registers or a
value from mfcr. It does set up to save/restore r14-r31 and floating point
registers as r46-r63.
The result is that if things get to the point of the following FreeBSD code as
part of handling the exception then the first _Unwind_SetGR gets a SEGV.
__builtin_eh_return_data_regno (0) returns 3 to identify r3 as the register
context.
678 /* For targets with pointers smaller than the word size, we must
extend the
679 pointer, and this extension is target dependent. */
680 _Unwind_SetGR (context, __builtin_eh_return_data_regno (0),
681 __builtin_extend_pointer (ue_header));
682 _Unwind_SetGR (context, __builtin_eh_return_data_regno (1),
683 handler_switch_value);
684 _Unwind_SetIP (context, landing_pad);
As evidence of the difference for scratch register handling (and "r70"/cr
handling). . .
gcc/g++ dwarfdump -v -v -F output extraction for _Unwind_RaiseException:
fde section offset 1104 0x00000450 cie offset for fde: 1108 0x00000454
0 DW_CFA_advance_loc 8 (8 * 1)
1 DW_CFA_def_cfa_offset 3024
4 DW_CFA_advance_loc1 156
6 DW_CFA_offset r4 -232 (58 * -4)
8 DW_CFA_offset r3 -236 (59 * -4)
10 DW_CFA_offset r28 -160 (40 * -4)
12 DW_CFA_offset r27 -164 (41 * -4)
14 DW_CFA_offset r26 -168 (42 * -4)
16 DW_CFA_offset r25 -172 (43 * -4)
18 DW_CFA_offset r24 -176 (44 * -4)
20 DW_CFA_offset r23 -180 (45 * -4)
22 DW_CFA_offset r22 -184 (46 * -4)
24 DW_CFA_offset r21 -188 (47 * -4)
26 DW_CFA_offset r20 -192 (48 * -4)
28 DW_CFA_offset r19 -196 (49 * -4)
30 DW_CFA_offset r18 -200 (50 * -4)
32 DW_CFA_offset r17 -204 (51 * -4)
34 DW_CFA_offset r16 -208 (52 * -4)
36 DW_CFA_offset r15 -212 (53 * -4)
38 DW_CFA_offset r14 -216 (54 * -4)
40 DW_CFA_offset r63 -8 (2 * -4)
42 DW_CFA_offset r62 -16 (4 * -4)
44 DW_CFA_offset r61 -24 (6 * -4)
46 DW_CFA_offset r60 -32 (8 * -4)
48 DW_CFA_offset r59 -40 (10 * -4)
50 DW_CFA_offset r58 -48 (12 * -4)
52 DW_CFA_offset r57 -56 (14 * -4)
54 DW_CFA_offset r56 -64 (16 * -4)
56 DW_CFA_offset r55 -72 (18 * -4)
58 DW_CFA_offset r54 -80 (20 * -4)
60 DW_CFA_offset r53 -88 (22 * -4)
62 DW_CFA_offset r52 -96 (24 * -4)
64 DW_CFA_offset r51 -104 (26 * -4)
66 DW_CFA_offset r50 -112 (28 * -4)
68 DW_CFA_offset r49 -120 (30 * -4)
70 DW_CFA_offset r48 -128 (32 * -4)
72 DW_CFA_offset r47 -136 (34 * -4)
74 DW_CFA_offset r46 -144 (36 * -4)
76 DW_CFA_register r70 = r12
79 DW_CFA_offset_extended_sf r65 4 (-1 * -4)
82 DW_CFA_advance_loc 32 (32 * 1)
83 DW_CFA_offset r5 -228 (57 * -4)
85 DW_CFA_offset r31 -148 (37 * -4)
87 DW_CFA_offset r30 -152 (38 * -4)
89 DW_CFA_offset r29 -156 (39 * -4)
91 DW_CFA_offset_extended r70 -220 (55 * -4)
94 DW_CFA_offset r6 -224 (56 * -4)
96 DW_CFA_nop
97 DW_CFA_nop
98 DW_CFA_nop
clang/clang++ 3.8.0 dwarfdump -v -v -F output extraction for
_Unwind_RaiseException:
fde section offset 692 0x000002b4 cie offset for fde: 696 0x000002b8
0 DW_CFA_advance_loc 20 (5 * 4)
1 DW_CFA_def_cfa_offset 2992
4 DW_CFA_offset r31 -148 (37 * -4)
6 DW_CFA_offset r30 -152 (38 * -4)
8 DW_CFA_offset_extended_sf r65 4 (-1 * -4)
11 DW_CFA_advance_loc 4 (1 * 4)
12 DW_CFA_def_cfa_register r31
14 DW_CFA_offset r14 -216 (54 * -4)
16 DW_CFA_offset r15 -212 (53 * -4)
18 DW_CFA_offset r16 -208 (52 * -4)
20 DW_CFA_offset r17 -204 (51 * -4)
22 DW_CFA_offset r18 -200 (50 * -4)
24 DW_CFA_offset r19 -196 (49 * -4)
26 DW_CFA_offset r20 -192 (48 * -4)
28 DW_CFA_offset r21 -188 (47 * -4)
30 DW_CFA_offset r22 -184 (46 * -4)
32 DW_CFA_offset r23 -180 (45 * -4)
34 DW_CFA_offset r24 -176 (44 * -4)
36 DW_CFA_offset r25 -172 (43 * -4)
38 DW_CFA_offset r26 -168 (42 * -4)
40 DW_CFA_offset r27 -164 (41 * -4)
42 DW_CFA_offset r28 -160 (40 * -4)
44 DW_CFA_offset r29 -156 (39 * -4)
46 DW_CFA_offset r30 -152 (38 * -4)
48 DW_CFA_offset r31 -148 (37 * -4)
50 DW_CFA_offset r46 -144 (36 * -4)
52 DW_CFA_offset r47 -136 (34 * -4)
54 DW_CFA_offset r48 -128 (32 * -4)
56 DW_CFA_offset r49 -120 (30 * -4)
58 DW_CFA_offset r50 -112 (28 * -4)
60 DW_CFA_offset r51 -104 (26 * -4)
62 DW_CFA_offset r52 -96 (24 * -4)
64 DW_CFA_offset r53 -88 (22 * -4)
66 DW_CFA_offset r54 -80 (20 * -4)
68 DW_CFA_offset r55 -72 (18 * -4)
70 DW_CFA_offset r56 -64 (16 * -4)
72 DW_CFA_offset r57 -56 (14 * -4)
74 DW_CFA_offset r58 -48 (12 * -4)
76 DW_CFA_offset r59 -40 (10 * -4)
78 DW_CFA_offset r60 -32 (8 * -4)
80 DW_CFA_offset r61 -24 (6 * -4)
82 DW_CFA_offset r62 -16 (4 * -4)
84 DW_CFA_offset r63 -8 (2 * -4)
86 DW_CFA_nop
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