[PATCH] genksyms: Fix parsing a declarator with a preceding attribute

[Nathan Chancellor <nathan@kernel.org>]

After commit 07919126ecfc ("netfilter: annotate NAT helper hook pointers
with __rcu"), genksyms fails to parse the __rcu annotation when building
with CONFIG_DEBUG_INFO_BTF=y, CONFIG_PAHOLE_HAS_BTF_TAG=y, and a version
of clang that supports btf_type_tag.

  $ clang --version | head -1
  ClangBuiltLinux clang version 22.1.0 (https://github.com/llvm/llvm-project.git 4434dabb69916856b824f68a64b029c67175e532)

  $ cat kernel/configs/repro.config
  CONFIG_BPF_SYSCALL=y
  CONFIG_MODVERSIONS=y
  # CONFIG_DEBUG_INFO_NONE is not set
  CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y
  CONFIG_DEBUG_INFO_BTF=y

  $ make -skj"$(nproc)" ARCH=x86_64 LLVM=1 mrproper defconfig repro.config all
  WARNING: modpost: EXPORT symbol "nf_nat_ftp_hook" [vmlinux] version generation failed, symbol will not be versioned.
  ...
  WARNING: modpost: EXPORT symbol "nf_nat_irc_hook" [vmlinux] version generation failed, symbol will not be versioned.
  ...

genksyms falls over parsing the __rcu attribute in the declarator:

  # Kernel reproducer
  $ make -skj"$(nproc)" ARCH=x86_64 KCFLAGS=-D__GENKSYMS__ LLVM=1 net/netfilter/nf_conntrack_ftp.i

  $ scripts/genksyms/genksyms -w <net/netfilter/nf_conntrack_ftp.i &| rg 'syntax error'
  include/linux/netfilter/nf_conntrack_ftp.h:29: syntax error
  net/netfilter/nf_conntrack_ftp.c:46: syntax error

  # Trivial reproducer
  $ cat test.c
  int (*func)(void *foo, int bar);
  int (__attribute__((btf_type_tag("rcu"))) *func_with_attr)(void *foo, int bar);

  $ scripts/genksyms/genksyms -w <test.c
  <stdin>:2: syntax error

Optionally allow an attribute to precede a declarator to resolve this
error and properly generate symbol versions.

Fixes: 07919126ecfc ("netfilter: annotate NAT helper hook pointers with __rcu")
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
I plan to take this via the Kbuild tree for 7.0.
---
 scripts/genksyms/parse.y | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/scripts/genksyms/parse.y b/scripts/genksyms/parse.y
index efdcf07c4eb6..cabcd146f3aa 100644
--- a/scripts/genksyms/parse.y
+++ b/scripts/genksyms/parse.y
@@ -325,8 +325,8 @@ direct_declarator:
 		{ $$ = $4; }
 	| direct_declarator BRACKET_PHRASE
 		{ $$ = $2; }
-	| '(' declarator ')'
-		{ $$ = $3; }
+	| '(' attribute_opt declarator ')'
+		{ $$ = $4; }
 	;
 
 /* Nested declarators differ from regular declarators in that they do

---
base-commit: 6de23f81a5e08be8fbf5e8d7e9febc72a5b5f27f
change-id: 20260224-genksyms-fix-attribute-declarator-9b3d63ba5caa

Best regards,
--  
Nathan Chancellor <nathan@kernel.org>