Re: [PATCH 01/17] kallsyms: support big kernel symbols (2-byte lengths)

Gary Guo
2021-07-04T22:20:19Z

On Sun, 4 Jul 2021 22:33:39 +0100
Matthew Wilcox <willy@infradead.org> wrote:

> On Sun, Jul 04, 2021 at 11:17:50PM +0200, Miguel Ojeda wrote:
> > On Sun, Jul 4, 2021 at 11:05 PM Matthew Wilcox
> > <willy@infradead.org> wrote:
> > >
> > > What happened to my suggestion from last time of encoding symbols
> > > < 128 as 0-127 and symbols larger than that as (data[0] - 128) *
> > > 256 + data[1]) ?
> >
> > Nothing, sorry, we focused on other parts (e.g. the allocation
> > panics) during this iteration. I can take a look for v2.
>
> Here's what I have. Build testing now.
>
>
> diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
> index c851ca0ed357..0d45a6e5fdc3 100644
> --- a/kernel/kallsyms.c
> +++ b/kernel/kallsyms.c
> @@ -67,6 +67,14 @@ static unsigned int
> kallsyms_expand_symbol(unsigned int off, len = *data;
> data++;
>
> + /* lengths larger than 128 are encoded as two bytes */
> + if (len >= 128) {
> + len -= 128;
> + len *= 256;
> + len += *data;
> + data++;
> + }
> +
> /*
> * Update the offset to return the offset for the next
> symbol on
> * the compressed stream.
> diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
> index 54ad86d13784..701566e01a1d 100644
> --- a/scripts/kallsyms.c
> +++ b/scripts/kallsyms.c
> @@ -467,10 +467,16 @@ static void write_src(void)
> output_label("kallsyms_names");
> off = 0;
> for (i = 0; i < table_cnt; i++) {
> + int len = table[i]->len;
> if ((i & 0xFF) == 0)
> markers[i >> 8] = off;
>
> - printf("\t.byte 0x%02x", table[i]->len);
> + if (len >= 128) {
> + printf("\t.byte 0x%02x\n", len / 256 + 128);
> + len %= 256;
> + off++;
> + }
> + printf("\t.byte 0x%02x", len);
> for (k = 0; k < table[i]->len; k++)
> printf(", 0x%02x", table[i]->sym[k]);
> printf("\n");

This is big endian.