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[bpf-next] bpf: temporarily define BPF_NO_PRESEVE_ACCESS_INDEX for GCC

Message ID 20240507095011.15867-1-jose.marchesi@oracle.com (mailing list archive)
State Accepted
Commit 675b4e24bc50f4600b6bf3527fdbaa1f73498334
Delegated to: BPF
Headers show
Series [bpf-next] bpf: temporarily define BPF_NO_PRESEVE_ACCESS_INDEX for GCC | expand

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Commit Message

Jose E. Marchesi May 7, 2024, 9:50 a.m. UTC 
The vmlinux.h file generated by bpftool makes use of compiler pragmas
in order to install the CO-RE preserve_access_index in all the struct
types derived from the BTF info:

  #ifndef __VMLINUX_H__
  #define __VMLINUX_H__

  #ifndef BPF_NO_PRESERVE_ACCESS_INDEX
  #pragma clang attribute push (__attribute__((preserve_access_index)), apply_t = record
  #endif

  [... type definitions generated from kernel BTF ... ]

  #ifndef BPF_NO_PRESERVE_ACCESS_INDEX
  #pragma clang attribute pop
  #endif

The `clang attribute push/pop' pragmas are specific to clang/llvm and
are not supported by GCC.

At the moment the BTF dumping services in libbpf do not support
dicriminating between types dumped because they are directly referred
and types dumped because they are dependencies.  A suitable API is
being worked now. See [1] and [2].

In the interim, this patch changes the selftests/bpf Makefile so it
passes -DBPF_NO_PRESERVE_ACCESS_INDEX to GCC when it builds the
selftests.  This workaround is temporary, and may have an impact on
the results of the GCC-built tests.

[1] https://lore.kernel.org/bpf/20240503111836.25275-1-jose.marchesi@oracle.com/T/#u
[2] https://lore.kernel.org/bpf/20240504205510.24785-1-jose.marchesi@oracle.com/T/#u

Tested in bpf-next master.
No regressions.

Signed-off-by: Jose E. Marchesi <jose.marchesi@oracle.com>
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Yonghong Song <yonghong.song@linux.dev>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: david.faust@oracle.com
Cc: cupertino.miranda@oracle.com
---
 tools/testing/selftests/bpf/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

patchwork-bot+netdevbpf@kernel.org May 7, 2024, 9:50 p.m. UTC | #1 
Hello:

This patch was applied to bpf/bpf-next.git (master)
by Andrii Nakryiko <andrii@kernel.org>:

On Tue,  7 May 2024 11:50:11 +0200 you wrote:
> The vmlinux.h file generated by bpftool makes use of compiler pragmas
> in order to install the CO-RE preserve_access_index in all the struct
> types derived from the BTF info:
> 
>   #ifndef __VMLINUX_H__
>   #define __VMLINUX_H__
> 
> [...]

Here is the summary with links:
  - [bpf-next] bpf: temporarily define BPF_NO_PRESEVE_ACCESS_INDEX for GCC
    https://git.kernel.org/bpf/bpf-next/c/675b4e24bc50

You are awesome, thank you!
diff mbox series

Patch

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index 5d9c906bc3cb..f0c429cf4424 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -431,7 +431,7 @@  endef
 # Build BPF object using GCC
 define GCC_BPF_BUILD_RULE
 	$(call msg,GCC-BPF,$(TRUNNER_BINARY),$2)
-	$(Q)$(BPF_GCC) $3 -Wno-attributes -O2 -c $1 -o $2
+	$(Q)$(BPF_GCC) $3 -DBPF_NO_PRESERVE_ACCESS_INDEX -Wno-attributes -O2 -c $1 -o $2
 endef
 
 SKEL_BLACKLIST := btf__% test_pinning_invalid.c test_sk_assign.c