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ld/dwarf: raise includestack to 256, clamp instead of abort #144

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Merged
staalmannen merged 1 commit into from
May 22, 2026
Merged

ld/dwarf: raise includestack to 256, clamp instead of abort #144

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11 changes: 5 additions & 6 deletions sys/src/cmd/ld/dwarf.c
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Original file line number Diff line number Diff line change
Expand Up @@ -513,12 +513,11 @@ addhistfile(char *zentry)
return histfilesize - 1;
}

// Go's runtime C sources are sane, and Go sources nest only 1 level,
// so 16 should be plenty.
// APE headers have deep transitive include chains; 256 covers real-world use.
static struct {
int file;
vlong line;
} includestack[64];
} includestack[256];
static int includetop;
static vlong absline;

Expand All @@ -542,9 +541,9 @@ checknesting(void)
errorexit();
}
if (includetop >= nelem(includestack)) {
diag("nesting too deep");
for (i = 0; i < nelem(includestack); i++)
diag("%s", histfile[includestack[i].file]); errorexit();
if(includetop == nelem(includestack))
diag("include nesting too deep, truncating DWARF line info");
includetop = nelem(includestack) - 1;
Comment on lines +544 to +546

@gemini-code-assist gemini-code-assist Bot May 22, 2026

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high

The clamping logic introduced here has two significant issues:

  1. Diagnostic Spam: Since includetop is reset to nelem(includestack) - 1, the next push will increment it back to nelem, triggering the diag message again. This will repeat for every include level and line change beyond the limit, flooding the output.

  2. Stack Underflow / Desynchronization: Clamping the stack pointer includetop causes it to lose sync with the actual nesting depth. When the nesting level decreases (pops), includetop will be decremented from the clamped value. Once the nesting returns to zero, includetop will become negative, likely triggering a fatal error (stack underflow) later in the execution. This defeats the purpose of making the limit non-fatal.

To fix the spam, use a static flag. It is also recommended to keep the stack trace (the loop over histfile) inside the if(!warned) block to help identify the cause of the deep nesting. To properly handle the nesting without aborting, you should ideally allow includetop to track the real depth but guard the array accesses to use a clamped index.

		static int warned;
		if(!warned){
			int i;
			diag("include nesting too deep, truncating DWARF line info");
			for(i = 0; i < nelem(includestack); i++)
				diag("%s", histfile[includestack[i].file]);
			warned = 1;
		}
		includetop = nelem(includestack) - 1;

}
}

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