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If a wl_array has size zero, wl_array_for_each computes NULL + 0 to get to the end pointer. This should be fine, and indeed it would be fine in C++. But the C specification has a mistake here and it is actually undefined behavior. See https://davidben.net/2024/01/15/empty-slices.html Clang's -fsanitize=undefined flags this. I ran into this in Chromium's build with wayland-scanner on one of our XML files. ../../third_party/wayland/src/src/scanner.c:1853:2: runtime error: applying zero offset to null pointer #0 0x55c979b8e02c in emit_code third_party/wayland/src/src/scanner.c:1853:2 #1 0x55c979b89323 in main third_party/wayland/src/src/scanner.c #2 0x7f8dfdb8c6c9 in __libc_start_call_main csu/../sysdeps/nptl/libc_start_call_main.h:58:16 #3 0x7f8dfdb8c784 in __libc_start_main csu/../csu/libc-start.c:360:3 #4 0x55c979b70f39 in _start (...) An empty XML file is sufficient to hit this case, so I've added it as a test. To reproduce, undo the fix and include only the test, then build with: CC=clang CFLAGS="-fno-sanitize-recover=undefined" meson build/ -Db_sanitize=undefined -Db_lundef=false ninja -C build test Signed-off-by: David Benjamin <davidben@google.com>
20 lines
338 B
C
20 lines
338 B
C
/* SCANNER TEST */
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#include <stdlib.h>
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#include <stdint.h>
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#include "wayland-util.h"
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static const struct wl_interface *empty_types[] = {
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};
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static const struct wl_message empty_requests[] = {
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{ "empty", "", empty_types + 0 },
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};
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WL_EXPORT const struct wl_interface empty_interface = {
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"empty", 1,
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1, empty_requests,
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0, NULL,
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};
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