Fix a crash when reporting an error at the end of a file #310
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The compiler crashes with a segmentation fault when an unterminated C-style comment exists at the very end of a file. The root cause is a buffer over-read in the error() function, which attempts to construct a diagnostic message by reading the source line containing the error. When the error is on the last line of a file without a trailing newline, this logic would read past the end of the source buffer. Fix the issue by adding a bounds check to the loop, ensuring it does not read beyond the source buffer's size. This allows the compiler to correctly report the "Unenclosed C-style comment" error instead of crashing.
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FWIW, this issue can be easily reproduced with the following example: int main() {
/* this is an unterminated comment
} |
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1 issue found across 1 file
Prompt for AI agents (all 1 issues)
Understand the root cause of the following 1 issues and fix them.
<file name="src/globals.c">
<violation number="1" location="src/globals.c:1398">
This loop initializes `offset` to `SOURCE->size`, which causes an out-of-bounds read on the first iteration when accessing `SOURCE->elements[offset]`. The loop should initialize `offset` to `SOURCE->size - 1` to access the last valid element.</violation>
</file>
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| for (offset = 0; | ||
| offset < MAX_SOURCE && SOURCE->elements[start_idx + offset] != '\n'; | ||
| offset < MAX_SOURCE && (start_idx + offset) < SOURCE->size && |
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This loop initializes offset to SOURCE->size, which causes an out-of-bounds read on the first iteration when accessing SOURCE->elements[offset]. The loop should initialize offset to SOURCE->size - 1 to access the last valid element.
Prompt for AI agents
Address the following comment on src/globals.c at line 1398:
<comment>This loop initializes `offset` to `SOURCE->size`, which causes an out-of-bounds read on the first iteration when accessing `SOURCE->elements[offset]`. The loop should initialize `offset` to `SOURCE->size - 1` to access the last valid element.</comment>
<file context>
@@ -1395,7 +1395,8 @@ void error(char *msg)
for (offset = 0;
- offset < MAX_SOURCE && SOURCE->elements[start_idx + offset] != '\n';
+ offset < MAX_SOURCE && (start_idx + offset) < SOURCE->size &&
+ SOURCE->elements[start_idx + offset] != '\n';
offset++) {
</file context>
DrXiao
approved these changes
Oct 11, 2025
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Thank @visitorckw for contributing! |
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The compiler crashes with a segmentation fault when an unterminated C-style comment exists at the very end of a file.
The root cause is a buffer over-read in the error() function, which attempts to construct a diagnostic message by reading the source line containing the error. When the error is on the last line of a file without a trailing newline, this logic would read past the end of the source buffer.
Fix the issue by adding a bounds check to the loop, ensuring it does not read beyond the source buffer's size. This allows the compiler to correctly report the "Unenclosed C-style comment" error instead of crashing.
Summary by cubic
Prevents a crash when reporting an error at EOF by adding a source-bounds check while building the diagnostic line. Unterminated C-style comments at the end of a file without a trailing newline now produce a proper error instead of a segfault.