linux-kernel - Re: [PATCH v3] selftests/vDSO: Explicit unsigned char conversion for elf

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Date: Mon, 6 May 2024 10:34:17 -0700
From: Edward Liaw <edliaw@...gle.com>
To: Justin Stitt <justinstitt@...gle.com>
Cc: David Laight <David.Laight@...lab.com>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Shuah Khan <shuah@...nel.org>, 
	Nathan Chancellor <nathan@...nel.org>, Nick Desaulniers <ndesaulniers@...gle.com>, 
	Bill Wendling <morbo@...gle.com>, "H. Peter Anvin" <hpa@...ux.intel.com>, Andy Lutomirski <luto@....edu>, 
	"linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>, 
	"kernel-team@...roid.com" <kernel-team@...roid.com>, "llvm@...ts.linux.dev" <llvm@...ts.linux.dev>
Subject: Re: [PATCH v3] selftests/vDSO: Explicit unsigned char conversion for elf_hash

On Mon, May 6, 2024 at 10:16 AM Justin Stitt <justinstitt@...gle.com> wrote:
>
> On Sun, May 5, 2024 at 6:21 AM David Laight <David.Laight@...lab.com> wrote:
> >
> > From: Justin Stitt
> > > Sent: 01 May 2024 20:55
> > ...
> > > > static unsigned long elf_hash(const unsigned char *name)
> > ...
> > > Is it possible to just change the types of the parameters of vdso_sym()
> > > or does that trigger even more warnings on the callsites of vdso_sym()?
> >
> > Isn't the problem the definition of elf_hash()?
> > A '\0' terminated string really ought to be 'char *' not 'unsigned char *'.
>
> Right, although note this comment just about its definition:
>
> /* Straight from the ELF specification. */
> static unsigned long elf_hash(const unsigned char *name)
> {
>
> which indeed matches [1]
>
> [1]: https://man.freebsd.org/cgi/man.cgi?query=elf_hash&sektion=3&apropos=0&manpath=FreeBSD+7.1-RELEASE

How about I move the type cast into elf_hash, like libelf does
https://sourceforge.net/p/elftoolchain/code/HEAD/tree/trunk/libelf/elf_hashc#l47

diff --git a/tools/testing/selftests/vDSO/parse_vdso.c
b/tools/testing/selftests/vDSO/parse_vdso.c
index 413f75620a35..33db8abd7d59 100644
--- a/tools/testing/selftests/vDSO/parse_vdso.c
+++ b/tools/testing/selftests/vDSO/parse_vdso.c
@@ -56,12 +56,15 @@ static struct vdso_info
 } vdso_info;

 /* Straight from the ELF specification. */
-static unsigned long elf_hash(const unsigned char *name)
+static unsigned long elf_hash(const char *name)
 {
  unsigned long h = 0, g;
- while (*name)
+ const unsigned char *s;
+
+ s = (const unsigned char *) name;
+ while (*s)
  {
- h = (h << 4) + *name++;
+ h = (h << 4) + *s++;
  if (g = h & 0xf0000000)
  h ^= g >> 24;
  h &= ~g;


>
> >
> >         David
> >
> > -
> > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> > Registration No: 1397386 (Wales)
> >