Re: [PATCH 1/3] lib: early_string: allow early usage of some string functions

From: Christophe Leroy
Date: Sat May 01 2021 - 03:50:30 EST

Le 30/04/2021 à 10:50, Christophe Leroy a écrit :

Le 30/04/2021 à 10:47, Christophe Leroy a écrit :

Le 30/04/2021 à 06:22, Daniel Walker a écrit :
This systems allows some string functions to be moved into
lib/early_string.c and they will be prepended with "early_" and compiled
without debugging like KASAN.

This is already done on x86 for,
"AMD Secure Memory Encryption (SME) support"

and on powerpc prom_init.c , and EFI's libstub.

The AMD memory feature disabled KASAN for all string functions, and
prom_init.c and efi libstub implement their own versions of the

This implementation allows sharing of the string functions without
removing the debugging features for the whole system.

This looks good. I prefer that rather than the way you proposed to do it two years ago.

Only one problem, see below.

+size_t strlcat(char *dest, const char *src, size_t count)
+    size_t dsize = strlen(dest);
+    size_t len = strlen(src);
+    size_t res = dsize + len;
+    /* This would be a bug */
+    BUG_ON(dsize >= count);

powerpc is not ready to handle BUG_ON() in when in prom_init.

Can you do:

     BUG_ON(dsize >= count);

In fact, should be like in prom_init today:

    if (dsize >= count)
        return count;
    BUG_ON(dsize >= count);

Thinking about it once more, this BUG_ON() is overkill and should be avoided, see

Therefore, something like the following would make it:

if (dsize >= count) {

return count;

+    dest += dsize;
+    count -= dsize;
+    if (len >= count)
+        len = count-1;
+    memcpy(dest, src, len);
+    dest[len] = 0;
+    return res;