diff mbox series

[bpf-next,2/4] selftests/bpf: convenience macro for use with 'asm volatile' blocks

Message ID 20221217021711.172247-3-eddyz87@gmail.com (mailing list archive)
State Changes Requested
Delegated to: BPF
Headers show
Series reduce BPF_ID_MAP_SIZE to fit only valid programs | expand

Checks

Context Check Description
netdev/tree_selection success Clearly marked for bpf-next, async
netdev/fixes_present success Fixes tag not required for -next series
netdev/subject_prefix success Link
netdev/cover_letter success Series has a cover letter
netdev/patch_count success Link
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 0 this patch: 0
netdev/cc_maintainers warning 12 maintainers not CCed: linux-kselftest@vger.kernel.org naveen.n.rao@linux.vnet.ibm.com kpsingh@kernel.org Kenta.Tada@sony.com haoluo@google.com song@kernel.org martin.lau@linux.dev sdf@google.com john.fastabend@gmail.com shuah@kernel.org jolsa@kernel.org mykolal@fb.com
netdev/build_clang success Errors and warnings before: 0 this patch: 0
netdev/module_param success Was 0 now: 0
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
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netdev/checkpatch fail ERROR: space prohibited before open square bracket '[' WARNING: line length of 90 exceeds 80 columns
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Commit Message

Eduard Zingerman Dec. 17, 2022, 2:17 a.m. UTC 
A set of macros useful for writing naked BPF functions using inline
assembly. E.g. as follows:

struct map_struct {
	...
} map SEC(".maps");

SEC(...)
__naked int foo_test(void)
{
	asm volatile(
		"r0 = 0;"
		"*(u64*)(r10 - 8) = r0;"
		"r1 = %[map] ll;"
		"r2 = r10;"
		"r2 += -8;"
		"call %[bpf_map_lookup_elem];"
		"r0 = 0;"
		"exit;"
		:
		: __imm(bpf_map_lookup_elem),
		  __imm_addr(map)
		: __clobber_all);
}

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
---
 tools/testing/selftests/bpf/progs/bpf_misc.h | 6 ++++++
 1 file changed, 6 insertions(+)

Comments

Yonghong Song Dec. 17, 2022, 6:58 p.m. UTC | #1 
On 12/16/22 6:17 PM, Eduard Zingerman wrote:
> A set of macros useful for writing naked BPF functions using inline
> assembly. E.g. as follows:
> 
> struct map_struct {
> 	...
> } map SEC(".maps");
> 
> SEC(...)
> __naked int foo_test(void)
> {
> 	asm volatile(
> 		"r0 = 0;"
> 		"*(u64*)(r10 - 8) = r0;"
> 		"r1 = %[map] ll;"
> 		"r2 = r10;"
> 		"r2 += -8;"
> 		"call %[bpf_map_lookup_elem];"
> 		"r0 = 0;"
> 		"exit;"
> 		:
> 		: __imm(bpf_map_lookup_elem),
> 		  __imm_addr(map)
> 		: __clobber_all);
> }
> 
> Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>

Acked-by: Yonghong Song <yhs@fb.com>
Andrii Nakryiko Dec. 20, 2022, 9:05 p.m. UTC | #2 
On Fri, Dec 16, 2022 at 6:17 PM Eduard Zingerman <eddyz87@gmail.com> wrote:
>
> A set of macros useful for writing naked BPF functions using inline
> assembly. E.g. as follows:
>
> struct map_struct {
>         ...
> } map SEC(".maps");
>
> SEC(...)
> __naked int foo_test(void)
> {
>         asm volatile(
>                 "r0 = 0;"
>                 "*(u64*)(r10 - 8) = r0;"
>                 "r1 = %[map] ll;"
>                 "r2 = r10;"
>                 "r2 += -8;"
>                 "call %[bpf_map_lookup_elem];"
>                 "r0 = 0;"
>                 "exit;"
>                 :
>                 : __imm(bpf_map_lookup_elem),
>                   __imm_addr(map)
>                 : __clobber_all);
> }
>
> Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
> ---
>  tools/testing/selftests/bpf/progs/bpf_misc.h | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/progs/bpf_misc.h b/tools/testing/selftests/bpf/progs/bpf_misc.h
> index a42363a3fef1..bbf56ad95636 100644
> --- a/tools/testing/selftests/bpf/progs/bpf_misc.h
> +++ b/tools/testing/selftests/bpf/progs/bpf_misc.h
> @@ -8,6 +8,12 @@
>  #define __log_level(lvl)       __attribute__((btf_decl_tag("comment:test_log_level="#lvl)))
>  #define __test_state_freq      __attribute__((btf_decl_tag("comment:test_state_freq")))
>
> +/* Convenience macro for use with 'asm volatile' blocks */
> +#define __naked __attribute__((naked))
> +#define __clobber_all "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r7", "r8", "r9", "memory"

I found that this one doesn't work well when passing some inputs as
registers (e.g., for address of a variable on stack). Compiler
complains that it couldn't find any free registers to use. So I ended
up using

#define __asm_common_clobbers "r0", "r1", "r2", "r3", "r4", "r5", "memory"

and adding "r6", "r7", etc manually, depending on the test.

So maybe let's add it upfront as `__clobber_common` as well?

But changes look good to me:

Acked-by: Andrii Nakryiko <andrii@kernel.org>

> +#define __imm(name) [name]"i"(name)
> +#define __imm_addr(name) [name]"i"(&name)
> +
>  #if defined(__TARGET_ARCH_x86)
>  #define SYSCALL_WRAPPER 1
>  #define SYS_PREFIX "__x64_"
> --
> 2.38.2
>
Eduard Zingerman Dec. 22, 2022, 12:12 a.m. UTC | #3 
On Tue, 2022-12-20 at 13:05 -0800, Andrii Nakryiko wrote:
> On Fri, Dec 16, 2022 at 6:17 PM Eduard Zingerman <eddyz87@gmail.com> wrote:
> > 
> > A set of macros useful for writing naked BPF functions using inline
> > assembly. E.g. as follows:
> > 
> > struct map_struct {
> >         ...
> > } map SEC(".maps");
> > 
> > SEC(...)
> > __naked int foo_test(void)
> > {
> >         asm volatile(
> >                 "r0 = 0;"
> >                 "*(u64*)(r10 - 8) = r0;"
> >                 "r1 = %[map] ll;"
> >                 "r2 = r10;"
> >                 "r2 += -8;"
> >                 "call %[bpf_map_lookup_elem];"
> >                 "r0 = 0;"
> >                 "exit;"
> >                 :
> >                 : __imm(bpf_map_lookup_elem),
> >                   __imm_addr(map)
> >                 : __clobber_all);
> > }
> > 
> > Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
> > ---
> >  tools/testing/selftests/bpf/progs/bpf_misc.h | 6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/tools/testing/selftests/bpf/progs/bpf_misc.h b/tools/testing/selftests/bpf/progs/bpf_misc.h
> > index a42363a3fef1..bbf56ad95636 100644
> > --- a/tools/testing/selftests/bpf/progs/bpf_misc.h
> > +++ b/tools/testing/selftests/bpf/progs/bpf_misc.h
> > @@ -8,6 +8,12 @@
> >  #define __log_level(lvl)       __attribute__((btf_decl_tag("comment:test_log_level="#lvl)))
> >  #define __test_state_freq      __attribute__((btf_decl_tag("comment:test_state_freq")))
> > 
> > +/* Convenience macro for use with 'asm volatile' blocks */
> > +#define __naked __attribute__((naked))
> > +#define __clobber_all "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r7", "r8", "r9", "memory"
> 
> I found that this one doesn't work well when passing some inputs as
> registers (e.g., for address of a variable on stack). Compiler
> complains that it couldn't find any free registers to use. So I ended
> up using
> 
> #define __asm_common_clobbers "r0", "r1", "r2", "r3", "r4", "r5", "memory"
> 
> and adding "r6", "r7", etc manually, depending on the test.
> 
> So maybe let's add it upfront as `__clobber_common` as well?

Will do.

> 
> But changes look good to me:
> 
> Acked-by: Andrii Nakryiko <andrii@kernel.org>
> 
> > +#define __imm(name) [name]"i"(name)
> > +#define __imm_addr(name) [name]"i"(&name)
> > +
> >  #if defined(__TARGET_ARCH_x86)
> >  #define SYSCALL_WRAPPER 1
> >  #define SYS_PREFIX "__x64_"
> > --
> > 2.38.2
> >
diff mbox series

Patch

diff --git a/tools/testing/selftests/bpf/progs/bpf_misc.h b/tools/testing/selftests/bpf/progs/bpf_misc.h
index a42363a3fef1..bbf56ad95636 100644
--- a/tools/testing/selftests/bpf/progs/bpf_misc.h
+++ b/tools/testing/selftests/bpf/progs/bpf_misc.h
@@ -8,6 +8,12 @@ 
 #define __log_level(lvl)	__attribute__((btf_decl_tag("comment:test_log_level="#lvl)))
 #define __test_state_freq	__attribute__((btf_decl_tag("comment:test_state_freq")))
 
+/* Convenience macro for use with 'asm volatile' blocks */
+#define __naked __attribute__((naked))
+#define __clobber_all "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r7", "r8", "r9", "memory"
+#define __imm(name) [name]"i"(name)
+#define __imm_addr(name) [name]"i"(&name)
+
 #if defined(__TARGET_ARCH_x86)
 #define SYSCALL_WRAPPER 1
 #define SYS_PREFIX "__x64_"