Re: [9front] 5l breakage on zynq

[ori@eigenstate.org]

> 
> ; hg revert -r 7667 /sys/src/cmd/^(5a 5c 5l cc 6c 6a 6l)
> 
> ... and rebuilding compilers/loaders and libc/libbio.
> 
> Any idea what broke?
> 
> Thanks,
> 

Yeah -- I think I see it:
	
	 1106		s = (Sym*)hunk;
	 1107		nhunk -= sizeof(Sym);
	 1108		hunk += sizeof(Sym);
	 1109	
	>1110		s->name = malloc(l);

This assumes that hunk is aligned, but the change to
malloc in the commit you flagged may leave it unaligned:

	void*
	alloc(long n)
	{
		void *p;
	
		while((uintptr)hunk & 7) {
			hunk++;
			nhunk--;
		}
		while(nhunk < n)
			gethunk();
		p = hunk;
		nhunk -= n;
		hunk += n;
		return p;
	}

Here, we always align the hunk on entry, but we ma
leave hunk unaligned on exit, if n is not a multiple
of 8. Then, when it's used directly, 's' is misaligned.

Try this patch, which aligns 'n' to a multiple of 8
before we allocate:

diff -r 965e0f59464d sys/src/cmd/cc/compat
--- a/sys/src/cmd/cc/compat	Sun May 10 22:51:40 2020 +0200
+++ b/sys/src/cmd/cc/compat	Tue May 12 08:02:58 2020 -0700
@@ -107,6 +107,7 @@
 {
 	void *p;
 
+	n = (n + 7) & (~7);
 	while((uintptr)hunk & 7) {
 		hunk++;
 		nhunk--;