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Fix misalignment of small structs in a Vector (C++) (#7883)

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* Rare fix: kick fix test

* Rare fix: real fix

* Rare fix: separate test

* Rare fix: remove comments

* Rare fix: updates

* Rare fix: less

* Rare fix: size_t switch to uoffset_t

* Rare fix: swap exp/val

* Rare fix: add annotated before/after

* Rare fix: remove unnecessary changes

---------

Co-authored-by: Derek Bailey <derekbailey@google.com>
This commit is contained in:
Pavlo Bashmakov
2023-09-28 22:53:50 -07:00
committed by GitHub
parent 053d39adaf
commit 15f16f149e
8 changed files with 138 additions and 6 deletions
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31
tests/alignment_test_before_fix.afb Normal file
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@@ -0,0 +1,31 @@
// Annotated Flatbuffer Binary
//
// Schema file: alignment_test.fbs
// Binary file: alignment_test_before_fix.bin
header:
+0x00 | 0C 00 00 00 | UOffset32 | 0x0000000C (12) Loc: 0x0C | offset to root table `SmallStructs`
padding:
+0x04 | 00 00 | uint8_t[2] | .. | padding
vtable (SmallStructs):
+0x06 | 06 00 | uint16_t | 0x0006 (6) | size of this vtable
+0x08 | 08 00 | uint16_t | 0x0008 (8) | size of referring table
+0x0A | 04 00 | VOffset16 | 0x0004 (4) | offset to field `small_structs` (id: 0)
root_table (SmallStructs):
+0x0C | 06 00 00 00 | SOffset32 | 0x00000006 (6) Loc: 0x06 | offset to vtable
+0x10 | 04 00 00 00 | UOffset32 | 0x00000004 (4) Loc: 0x14 | offset to field `small_structs` (vector)
vector (SmallStructs.small_structs):
+0x14 | 03 00 00 00 | uint32_t | 0x00000003 (3) | length of vector (# items)
+0x18 | 00 | uint8_t | 0x00 (0) | struct field `[0].var_0` of 'JustSmallStruct' (UByte)
+0x19 | 00 | uint8_t | 0x00 (0) | struct field `[0].var_1` of 'JustSmallStruct' (UByte)
+0x1A | 02 | uint8_t | 0x02 (2) | struct field `[1].var_0` of 'JustSmallStruct' (UByte)
+0x1B | 01 | uint8_t | 0x01 (1) | struct field `[1].var_1` of 'JustSmallStruct' (UByte)
+0x1C | 03 | uint8_t | 0x03 (3) | struct field `[2].var_0` of 'JustSmallStruct' (UByte)
+0x1D | 01 | uint8_t | 0x01 (1) | struct field `[2].var_1` of 'JustSmallStruct' (UByte)
unknown (no known references):
+0x1E | 04 01 | ?uint8_t[2] | .. | WARN: could be corrupted padding region.