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Date: Mon, 25 May 2015 18:46:29 -0400
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: ppc soft-float regression
On Mon, May 25, 2015 at 05:45:12PM -0400, Rich Felker wrote:
> @@ -74,6 +77,16 @@ void _dlstart_c(size_t *sp, size_t *dynv)
> *rel_addr = (size_t)base + rel[2];
> }
>
> + /* Prepare storage for stages 2 to save clobbered REL
> + * addends so they can be reused in stage 3. There should
> + * be very few. If something goes wrong and there are a
> + * huge number, pass a null pointer to trigger stage 2
> + * to abort instead of risking stack overflow. */
> + int too_many_addends = symbolic_rel_cnt > 4096;
> + size_t naddends = too_many_addends ? 1 : symbolic_rel_cnt;
> + size_t addends[naddends];
> + size_t *paddends = too_many_addends ? 0 : addends;
> +
> const char *strings = (void *)(base + dyn[DT_STRTAB]);
> const Sym *syms = (void *)(base + dyn[DT_SYMTAB]);
This logic could lead to a zero-sized VLA (thus UB); instead, trying:
int too_many_addends = symbolic_rel_cnt > 4096;
size_t naddends = too_many_addends ? 0 : symbolic_rel_cnt;
size_t addends[naddends+1];
size_t *paddends = too_many_addends ? 0 : addends;
Avoiding the wasteful +1 would involve more conditionals so I think
it's best just avoiding it. Alternatively this might be
simpler/smaller:
size_t addends[symbolic_rel_cnt & LIMIT-1 | 1];
size_t *paddends = symbolic_rel_cnt >= LIMIT ? 0 : addends;
Rich
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