Fix test_bpf_syscall_macro selftest on powerpc

[PATCH 2/3] libbpf: Remove powerpc prefix from syscall function names

Posted by Saket Kumar Bhaskar 2 weeks, 6 days ago

Since commit 94746890202cf ("powerpc: Don't add __powerpc_ prefix to
syscall entry points") drops _powerpc prefix to syscall entry points,
even though powerpc now supports syscall wrapper, so /proc/kallsyms
have symbols for syscall entry without powerpc prefix(sys_*).

For this reason, arch specific prefix for syscall functions in powerpc
is dropped.

Signed-off-by: Saket Kumar Bhaskar <skb99@linux.ibm.com>
---
 tools/lib/bpf/libbpf.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 219facd0e66e..3a370fa37d8a 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -11110,9 +11110,7 @@ static const char *arch_specific_syscall_pfx(void)
 #elif defined(__riscv)
 	return "riscv";
 #elif defined(__powerpc__)
-	return "powerpc";
-#elif defined(__powerpc64__)
-	return "powerpc64";
+	return "";
 #else
 	return NULL;
 #endif
@@ -11127,7 +11125,11 @@ int probe_kern_syscall_wrapper(int token_fd)
 	if (!ksys_pfx)
 		return 0;
 
+#if defined(__powerpc__)
+	snprintf(syscall_name, sizeof(syscall_name), "sys_bpf");
+#else
 	snprintf(syscall_name, sizeof(syscall_name), "__%s_sys_bpf", ksys_pfx);
+#endif
 
 	if (determine_kprobe_perf_type() >= 0) {
 		int pfd;
@@ -11272,8 +11274,12 @@ struct bpf_link *bpf_program__attach_ksyscall(const struct bpf_program *prog,
 		 * compiler does not know that we have an explicit conditional
 		 * as well.
 		 */
+#if defined(__powerpc__)
+		snprintf(func_name, sizeof(func_name), "sys_%s", syscall_name);
+#else
 		snprintf(func_name, sizeof(func_name), "__%s_sys_%s",
 			 arch_specific_syscall_pfx() ? : "", syscall_name);
+#endif
 	} else {
 		snprintf(func_name, sizeof(func_name), "__se_sys_%s", syscall_name);
 	}
-- 
2.43.5

Re: [PATCH 2/3] libbpf: Remove powerpc prefix from syscall function names

Posted by Andrii Nakryiko 2 weeks, 1 day ago

On Sun, Nov 3, 2024 at 9:00 PM Saket Kumar Bhaskar <skb99@linux.ibm.com> wrote:
>
> Since commit 94746890202cf ("powerpc: Don't add __powerpc_ prefix to
> syscall entry points") drops _powerpc prefix to syscall entry points,
> even though powerpc now supports syscall wrapper, so /proc/kallsyms
> have symbols for syscall entry without powerpc prefix(sys_*).
>
> For this reason, arch specific prefix for syscall functions in powerpc
> is dropped.
>
> Signed-off-by: Saket Kumar Bhaskar <skb99@linux.ibm.com>
> ---
>  tools/lib/bpf/libbpf.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 219facd0e66e..3a370fa37d8a 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -11110,9 +11110,7 @@ static const char *arch_specific_syscall_pfx(void)
>  #elif defined(__riscv)
>         return "riscv";
>  #elif defined(__powerpc__)
> -       return "powerpc";
> -#elif defined(__powerpc64__)
> -       return "powerpc64";
> +       return "";
>  #else
>         return NULL;
>  #endif
> @@ -11127,7 +11125,11 @@ int probe_kern_syscall_wrapper(int token_fd)
>         if (!ksys_pfx)
>                 return 0;
>
> +#if defined(__powerpc__)
> +       snprintf(syscall_name, sizeof(syscall_name), "sys_bpf");
> +#else
>         snprintf(syscall_name, sizeof(syscall_name), "__%s_sys_bpf", ksys_pfx);
> +#endif

The problem is that on older versions of kernel it will have this
prefix, while on newer ones it won't. So to not break anything on old
kernels, we'd need to do feature detection and pick whether to use
prefix or not, right?

So it seems like this change needs a bit more work.

pw-bot: cr

>
>         if (determine_kprobe_perf_type() >= 0) {
>                 int pfd;
> @@ -11272,8 +11274,12 @@ struct bpf_link *bpf_program__attach_ksyscall(const struct bpf_program *prog,
>                  * compiler does not know that we have an explicit conditional
>                  * as well.
>                  */
> +#if defined(__powerpc__)
> +               snprintf(func_name, sizeof(func_name), "sys_%s", syscall_name);
> +#else
>                 snprintf(func_name, sizeof(func_name), "__%s_sys_%s",
>                          arch_specific_syscall_pfx() ? : "", syscall_name);
> +#endif
>         } else {
>                 snprintf(func_name, sizeof(func_name), "__se_sys_%s", syscall_name);
>         }
> --
> 2.43.5
>

Re: [PATCH 2/3] libbpf: Remove powerpc prefix from syscall function names

Posted by Saket Kumar Bhaskar 4 days ago

On Fri, Nov 08, 2024 at 10:43:54AM -0800, Andrii Nakryiko wrote:
> On Sun, Nov 3, 2024 at 9:00 PM Saket Kumar Bhaskar <skb99@linux.ibm.com> wrote:
> >
> > Since commit 94746890202cf ("powerpc: Don't add __powerpc_ prefix to
> > syscall entry points") drops _powerpc prefix to syscall entry points,
> > even though powerpc now supports syscall wrapper, so /proc/kallsyms
> > have symbols for syscall entry without powerpc prefix(sys_*).
> >
> > For this reason, arch specific prefix for syscall functions in powerpc
> > is dropped.
> >
> > Signed-off-by: Saket Kumar Bhaskar <skb99@linux.ibm.com>
> > ---
> >  tools/lib/bpf/libbpf.c | 12 +++++++++---
> >  1 file changed, 9 insertions(+), 3 deletions(-)
> >
> > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> > index 219facd0e66e..3a370fa37d8a 100644
> > --- a/tools/lib/bpf/libbpf.c
> > +++ b/tools/lib/bpf/libbpf.c
> > @@ -11110,9 +11110,7 @@ static const char *arch_specific_syscall_pfx(void)
> >  #elif defined(__riscv)
> >         return "riscv";
> >  #elif defined(__powerpc__)
> > -       return "powerpc";
> > -#elif defined(__powerpc64__)
> > -       return "powerpc64";
> > +       return "";
> >  #else
> >         return NULL;
> >  #endif
> > @@ -11127,7 +11125,11 @@ int probe_kern_syscall_wrapper(int token_fd)
> >         if (!ksys_pfx)
> >                 return 0;
> >
> > +#if defined(__powerpc__)
> > +       snprintf(syscall_name, sizeof(syscall_name), "sys_bpf");
> > +#else
> >         snprintf(syscall_name, sizeof(syscall_name), "__%s_sys_bpf", ksys_pfx);
> > +#endif
> 
> The problem is that on older versions of kernel it will have this
> prefix, while on newer ones it won't. So to not break anything on old
> kernels, we'd need to do feature detection and pick whether to use
> prefix or not, right?
> 
> So it seems like this change needs a bit more work.
> 
> pw-bot: cr
> 
Hi Andrii,

IMO since both the patches 7e92e01b7245(powerpc: Provide syscall wrapper) 
and 94746890202cf(powerpc: Don't add __powerpc_ prefix to syscall entry points) 
went into the same kernel version v6.1-rc1, there won't me much kernel
versions that has only one of these patches.

Also, to test more I tried this patch with ARCH_HAS_SYSCALL_WRAPPER disabled,
and it the test passed in this case too.

Thanks,
Saket
> >
> >         if (determine_kprobe_perf_type() >= 0) {
> >                 int pfd;
> > @@ -11272,8 +11274,12 @@ struct bpf_link *bpf_program__attach_ksyscall(const struct bpf_program *prog,
> >                  * compiler does not know that we have an explicit conditional
> >                  * as well.
> >                  */
> > +#if defined(__powerpc__)
> > +               snprintf(func_name, sizeof(func_name), "sys_%s", syscall_name);
> > +#else
> >                 snprintf(func_name, sizeof(func_name), "__%s_sys_%s",
> >                          arch_specific_syscall_pfx() ? : "", syscall_name);
> > +#endif
> >         } else {
> >                 snprintf(func_name, sizeof(func_name), "__se_sys_%s", syscall_name);
> >         }
> > --
> > 2.43.5
> >

Re: [PATCH 2/3] libbpf: Remove powerpc prefix from syscall function names

Posted by Andrii Nakryiko 2 days, 15 hours ago

On Wed, Nov 20, 2024 at 6:52 AM Saket Kumar Bhaskar <skb99@linux.ibm.com> wrote:
>
> On Fri, Nov 08, 2024 at 10:43:54AM -0800, Andrii Nakryiko wrote:
> > On Sun, Nov 3, 2024 at 9:00 PM Saket Kumar Bhaskar <skb99@linux.ibm.com> wrote:
> > >
> > > Since commit 94746890202cf ("powerpc: Don't add __powerpc_ prefix to
> > > syscall entry points") drops _powerpc prefix to syscall entry points,
> > > even though powerpc now supports syscall wrapper, so /proc/kallsyms
> > > have symbols for syscall entry without powerpc prefix(sys_*).
> > >
> > > For this reason, arch specific prefix for syscall functions in powerpc
> > > is dropped.
> > >
> > > Signed-off-by: Saket Kumar Bhaskar <skb99@linux.ibm.com>
> > > ---
> > >  tools/lib/bpf/libbpf.c | 12 +++++++++---
> > >  1 file changed, 9 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> > > index 219facd0e66e..3a370fa37d8a 100644
> > > --- a/tools/lib/bpf/libbpf.c
> > > +++ b/tools/lib/bpf/libbpf.c
> > > @@ -11110,9 +11110,7 @@ static const char *arch_specific_syscall_pfx(void)
> > >  #elif defined(__riscv)
> > >         return "riscv";
> > >  #elif defined(__powerpc__)
> > > -       return "powerpc";
> > > -#elif defined(__powerpc64__)
> > > -       return "powerpc64";
> > > +       return "";
> > >  #else
> > >         return NULL;
> > >  #endif
> > > @@ -11127,7 +11125,11 @@ int probe_kern_syscall_wrapper(int token_fd)
> > >         if (!ksys_pfx)
> > >                 return 0;
> > >
> > > +#if defined(__powerpc__)
> > > +       snprintf(syscall_name, sizeof(syscall_name), "sys_bpf");
> > > +#else
> > >         snprintf(syscall_name, sizeof(syscall_name), "__%s_sys_bpf", ksys_pfx);
> > > +#endif
> >
> > The problem is that on older versions of kernel it will have this
> > prefix, while on newer ones it won't. So to not break anything on old
> > kernels, we'd need to do feature detection and pick whether to use
> > prefix or not, right?
> >
> > So it seems like this change needs a bit more work.
> >
> > pw-bot: cr
> >
> Hi Andrii,
>
> IMO since both the patches 7e92e01b7245(powerpc: Provide syscall wrapper)
> and 94746890202cf(powerpc: Don't add __powerpc_ prefix to syscall entry points)
> went into the same kernel version v6.1-rc1, there won't me much kernel
> versions that has only one of these patches.
>
> Also, to test more I tried this patch with ARCH_HAS_SYSCALL_WRAPPER disabled,
> and it the test passed in this case too.
>

Keep in mind that libbpf is supposed to work across many kernel
versions. So as long as there are powerpc (old) kernels that do use
arch-specific prefix, we need to detect them and supply prefix when
attaching ksyscall programs.

> Thanks,
> Saket
> > >
> > >         if (determine_kprobe_perf_type() >= 0) {
> > >                 int pfd;
> > > @@ -11272,8 +11274,12 @@ struct bpf_link *bpf_program__attach_ksyscall(const struct bpf_program *prog,
> > >                  * compiler does not know that we have an explicit conditional
> > >                  * as well.
> > >                  */
> > > +#if defined(__powerpc__)
> > > +               snprintf(func_name, sizeof(func_name), "sys_%s", syscall_name);
> > > +#else
> > >                 snprintf(func_name, sizeof(func_name), "__%s_sys_%s",
> > >                          arch_specific_syscall_pfx() ? : "", syscall_name);
> > > +#endif
> > >         } else {
> > >                 snprintf(func_name, sizeof(func_name), "__se_sys_%s", syscall_name);
> > >         }
> > > --
> > > 2.43.5
> > >