[v3] selftests/vDSO: Explicit unsigned char conversion for elf_hash

[PATCH v3] selftests/vDSO: Explicit unsigned char conversion for elf_hash

Posted by Edward Liaw 1 year, 7 months ago

Fixes clang compilation warnings by adding explicit unsigned conversion:

parse_vdso.c:206:22: warning: passing 'const char *' to parameter of
 type 'const unsigned char *' converts between pointers to integer types
 where one is of the unique plain 'char' type and the other is not
 [-Wpointer-sign]
        ver_hash = elf_hash(version);
                            ^~~~~~~
parse_vdso.c:59:52: note: passing argument to parameter 'name' here
static unsigned long elf_hash(const unsigned char *name)
                                                   ^
parse_vdso.c:207:46: warning: passing 'const char *' to parameter of
 type 'const unsigned char *' converts between pointers to integer types
 where one is of the unique plain 'char' type and the other is not
 [-Wpointer-sign]
        ELF(Word) chain = vdso_info.bucket[elf_hash(name) % vdso_info.nbucket];
                                                    ^~~~
parse_vdso.c:59:52: note: passing argument to parameter 'name' here
static unsigned long elf_hash(const unsigned char *name)

Fixes: 98eedc3a9dbf ("Document the vDSO and add a reference parser")
Signed-off-by: Edward Liaw <edliaw@google.com>
---
v2: update commit message with correct compiler warning
v3: fix checkpatch errors and indentation
---
 tools/testing/selftests/vDSO/parse_vdso.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/vDSO/parse_vdso.c b/tools/testing/selftests/vDSO/parse_vdso.c
index 413f75620a35..9e29ff0657ea 100644
--- a/tools/testing/selftests/vDSO/parse_vdso.c
+++ b/tools/testing/selftests/vDSO/parse_vdso.c
@@ -203,8 +203,9 @@ void *vdso_sym(const char *version, const char *name)
 	if (!vdso_info.valid)
 		return 0;

-	ver_hash = elf_hash(version);
-	ELF(Word) chain = vdso_info.bucket[elf_hash(name) % vdso_info.nbucket];
+	ver_hash = elf_hash((const unsigned char *)version);
+	ELF(Word) chain = vdso_info.bucket[
+		elf_hash((const unsigned char *)name) % vdso_info.nbucket];

 	for (; chain != STN_UNDEF; chain = vdso_info.chain[chain]) {
 		ELF(Sym) *sym = &vdso_info.symtab[chain];
--
2.45.0.rc0.197.gbae5840b3b-goog

Re: [PATCH v3] selftests/vDSO: Explicit unsigned char conversion for elf_hash

Posted by Justin Stitt 1 year, 7 months ago

Hi,

On Wed, May 01, 2024 at 06:06:18PM +0000, Edward Liaw wrote:
> Fixes clang compilation warnings by adding explicit unsigned conversion:
> 
> parse_vdso.c:206:22: warning: passing 'const char *' to parameter of
>  type 'const unsigned char *' converts between pointers to integer types
>  where one is of the unique plain 'char' type and the other is not
>  [-Wpointer-sign]
>         ver_hash = elf_hash(version);
>                             ^~~~~~~
> parse_vdso.c:59:52: note: passing argument to parameter 'name' here
> static unsigned long elf_hash(const unsigned char *name)
>                                                    ^
> parse_vdso.c:207:46: warning: passing 'const char *' to parameter of
>  type 'const unsigned char *' converts between pointers to integer types
>  where one is of the unique plain 'char' type and the other is not
>  [-Wpointer-sign]
>         ELF(Word) chain = vdso_info.bucket[elf_hash(name) % vdso_info.nbucket];
>                                                     ^~~~
> parse_vdso.c:59:52: note: passing argument to parameter 'name' here
> static unsigned long elf_hash(const unsigned char *name)
> 
> Fixes: 98eedc3a9dbf ("Document the vDSO and add a reference parser")
> Signed-off-by: Edward Liaw <edliaw@google.com>

> ---
> v2: update commit message with correct compiler warning
> v3: fix checkpatch errors and indentation
> ---
>  tools/testing/selftests/vDSO/parse_vdso.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/vDSO/parse_vdso.c b/tools/testing/selftests/vDSO/parse_vdso.c
> index 413f75620a35..9e29ff0657ea 100644
> --- a/tools/testing/selftests/vDSO/parse_vdso.c
> +++ b/tools/testing/selftests/vDSO/parse_vdso.c
> @@ -203,8 +203,9 @@ void *vdso_sym(const char *version, const 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()?

Either way, this looks ok to me.

Acked-by: Justin Stitt <justinstitt@google.com>

>  	if (!vdso_info.valid)
>  		return 0;
> 
> -	ver_hash = elf_hash(version);
> -	ELF(Word) chain = vdso_info.bucket[elf_hash(name) % vdso_info.nbucket];
> +	ver_hash = elf_hash((const unsigned char *)version);
> +	ELF(Word) chain = vdso_info.bucket[
> +		elf_hash((const unsigned char *)name) % vdso_info.nbucket];
> 
>  	for (; chain != STN_UNDEF; chain = vdso_info.chain[chain]) {
>  		ELF(Sym) *sym = &vdso_info.symtab[chain];
> --
> 2.45.0.rc0.197.gbae5840b3b-goog
> 

Thanks
Justin

RE: [PATCH v3] selftests/vDSO: Explicit unsigned char conversion for elf_hash

Posted by David Laight 1 year, 7 months ago

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 *'.

	David

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

Re: [PATCH v3] selftests/vDSO: Explicit unsigned char conversion for elf_hash

Posted by Justin Stitt 1 year, 7 months ago

On Sun, May 5, 2024 at 6:21 AM David Laight <David.Laight@aculab.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

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

Re: [PATCH v3] selftests/vDSO: Explicit unsigned char conversion for elf_hash

Posted by Edward Liaw 1 year, 7 months ago

On Mon, May 6, 2024 at 10:16 AM Justin Stitt <justinstitt@google.com> wrote:
>
> On Sun, May 5, 2024 at 6:21 AM David Laight <David.Laight@aculab.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_hash.c#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)
> >

RE: [PATCH v3] selftests/vDSO: Explicit unsigned char conversion for elf_hash

Posted by David Laight 1 year, 7 months ago

From: Edward Liaw
> Sent: 06 May 2024 18:34
> 
> On Mon, May 6, 2024 at 10:16 AM Justin Stitt <justinstitt@google.com> wrote:
> >
> > On Sun, May 5, 2024 at 6:21 AM David Laight <David.Laight@aculab.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_hash.c#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;

That makes a lot more sense.

	David

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

Re: [PATCH v3] selftests/vDSO: Explicit unsigned char conversion for elf_hash

Posted by Edward Liaw 1 year, 7 months ago

On Mon, May 6, 2024 at 12:32 PM David Laight <David.Laight@aculab.com> wrote:
>
>
> That makes a lot more sense.

I sent v4 https://lore.kernel.org/all/20240506181951.1804451-1-edliaw@google.com/.
I updated the commit log to reflect the change but I'm not sure if I
did it right for the mailing list.  Should I have added --in-reply-to
this thread?

Edward

Re: [PATCH v3] selftests/vDSO: Explicit unsigned char conversion for elf_hash

Posted by Edward Liaw 1 year, 7 months ago

On Wed, May 1, 2024 at 12:54 PM Justin Stitt <justinstitt@google.com> wrote:
>
> Hi,
>
> On Wed, May 01, 2024 at 06:06:18PM +0000, Edward Liaw wrote:
> > Fixes clang compilation warnings by adding explicit unsigned conversion:
> >
> > parse_vdso.c:206:22: warning: passing 'const char *' to parameter of
> >  type 'const unsigned char *' converts between pointers to integer types
> >  where one is of the unique plain 'char' type and the other is not
> >  [-Wpointer-sign]
> >         ver_hash = elf_hash(version);
> >                             ^~~~~~~
> > parse_vdso.c:59:52: note: passing argument to parameter 'name' here
> > static unsigned long elf_hash(const unsigned char *name)
> >                                                    ^
> > parse_vdso.c:207:46: warning: passing 'const char *' to parameter of
> >  type 'const unsigned char *' converts between pointers to integer types
> >  where one is of the unique plain 'char' type and the other is not
> >  [-Wpointer-sign]
> >         ELF(Word) chain = vdso_info.bucket[elf_hash(name) % vdso_info.nbucket];
> >                                                     ^~~~
> > parse_vdso.c:59:52: note: passing argument to parameter 'name' here
> > static unsigned long elf_hash(const unsigned char *name)
> >
> > Fixes: 98eedc3a9dbf ("Document the vDSO and add a reference parser")
> > Signed-off-by: Edward Liaw <edliaw@google.com>
>
> > ---
> > v2: update commit message with correct compiler warning
> > v3: fix checkpatch errors and indentation
> > ---
> >  tools/testing/selftests/vDSO/parse_vdso.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/tools/testing/selftests/vDSO/parse_vdso.c b/tools/testing/selftests/vDSO/parse_vdso.c
> > index 413f75620a35..9e29ff0657ea 100644
> > --- a/tools/testing/selftests/vDSO/parse_vdso.c
> > +++ b/tools/testing/selftests/vDSO/parse_vdso.c
> > @@ -203,8 +203,9 @@ void *vdso_sym(const char *version, const 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()?

It does trigger more warnings on the callsites unfortunately.

>
> Either way, this looks ok to me.
>
> Acked-by: Justin Stitt <justinstitt@google.com>
>
> >       if (!vdso_info.valid)
> >               return 0;
> >
> > -     ver_hash = elf_hash(version);
> > -     ELF(Word) chain = vdso_info.bucket[elf_hash(name) % vdso_info.nbucket];
> > +     ver_hash = elf_hash((const unsigned char *)version);
> > +     ELF(Word) chain = vdso_info.bucket[
> > +             elf_hash((const unsigned char *)name) % vdso_info.nbucket];
> >
> >       for (; chain != STN_UNDEF; chain = vdso_info.chain[chain]) {
> >               ELF(Sym) *sym = &vdso_info.symtab[chain];
> > --
> > 2.45.0.rc0.197.gbae5840b3b-goog
> >
>
> Thanks
> Justin