[binutils-gdb/gdb-17-branch] GDB: aarch64-linux: Fix build failure on musl systems

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=1ccc3f6a2e28fa1f3357826374cba165b3ba3ff7

commit 1ccc3f6a2e28fa1f3357826374cba165b3ba3ff7
Author: Thiago Jung Bauermann <[email protected]>
Date:   Wed Feb 11 04:54:28 2026 +0000

    GDB: aarch64-linux: Fix build failure on musl systems
    
    (cherry picked from commit 02090062127d59978ccc312dabf63c6ea838cd85)
    
    When building against musl (e.g. on Alpine Linux), the following error
    happens:
    
        CXX    linux-aarch64-low.o
      In file included from /home/bauermann/src/binutils-gdb/gdbserver/linux-aarch64-low.cc:42:
      /home/bauermann/src/binutils-gdb/gdbserver/../gdb/arch/aarch64-gcs-linux.h:35:8: error: redefinition of 'struct user_gcs'
         35 | struct user_gcs
            |        ^~~~~~~~
      In file included from /home/bauermann/src/binutils-gdb/gdbserver/linux-aarch64-low.cc:35:
      /usr/include/asm/ptrace.h:329:8: note: previous definition of 'struct user_gcs'
        329 | struct user_gcs {
            |        ^~~~~~~~
      make[2]: *** [Makefile:565: linux-aarch64-low.o] Error 1
    
    aarch64-linux-tdep.c fails to build in the same way.  This happens because
    aarch64-gcs-linux.h uses GCS_MAGIC to see whether the system headers
    have GCS-related definitions.  The problem is that GCS_MAGIC is defined in
    <asm/sigcontext.h> while struct gcs_user is defined in <asm/ptrace.h>.
    It's fine on glibc systems because in the set of system headers that
    linux-aarch64-low.cc and aarch64-linux-tdep.c include, <asm/sigcontext.h>
    ends up being included implicitly as well.  This doesn't happen when using
    musl's headers though.
    
    There isn't a macro in <asm/ptrace.h> whose presence is correlated with
    the presence of the struct user_gcs definition, so a configure check is
    needed to detect it and conditionally define the struct.
    
    Also, this change requires aarch64-linux-tdep.c to stop using
    struct user_gcs because target-dependent code can't include <asm/ptrace.h>
    and thus even if HAVE_STRUCT_USER_GCS is set, the file won't have the
    struct definition available. To fix this problem, also backport the
    definition of AARCH64_LINUX_SIZEOF_GCS_REGSET and use it there.
    
    Note that there's another build issue with musl, described in
    PR gdb/33747 affecting compilation of gdb/ser-unix.c.  In order to be
    able to test this patch, I applied the patch in comment 11 there.
    
    Tested with a native build on an Alpine Linux aarch64 system, and also
    verified that all gdb.arch/aarch64-gcs*.exp tests pass on it.
    
    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=33926
    Co-authored-by: Chris Packham <[email protected]>
    Approved-By: Andrew Burgess <[email protected]>

Diff:
---
 gdb/aarch64-linux-tdep.c     |  5 +++--
 gdb/arch/aarch64-gcs-linux.h |  8 +++++---
 gdbsupport/config.in         |  3 +++
 gdbsupport/configure         | 36 ++++++++++++++++++++++++++++++++++++
 gdbsupport/configure.ac      | 19 +++++++++++++++++++
 5 files changed, 66 insertions(+), 5 deletions(-)

diff --git a/gdb/aarch64-linux-tdep.c b/gdb/aarch64-linux-tdep.c
index 76bde85188b..6c402e7ecdd 100644
--- a/gdb/aarch64-linux-tdep.c
+++ b/gdb/aarch64-linux-tdep.c
@@ -1684,8 +1684,9 @@ aarch64_linux_iterate_over_regset_sections (struct gdbarch *gdbarch,
 	  gcs_regmap, regcache_supply_regset, regcache_collect_regset
 	};
 
-      cb (".reg-aarch-gcs", sizeof (user_gcs), sizeof (user_gcs),
-	  &aarch64_linux_gcs_regset, "GCS registers", cb_data);
+      cb (".reg-aarch-gcs", AARCH64_LINUX_SIZEOF_GCS_REGSET,
+	  AARCH64_LINUX_SIZEOF_GCS_REGSET, &aarch64_linux_gcs_regset,
+	  "GCS registers", cb_data);
     }
 }
 
diff --git a/gdb/arch/aarch64-gcs-linux.h b/gdb/arch/aarch64-gcs-linux.h
index 018ca37a522..632823a8120 100644
--- a/gdb/arch/aarch64-gcs-linux.h
+++ b/gdb/arch/aarch64-gcs-linux.h
@@ -27,8 +27,7 @@
 #define HWCAP_GCS (1ULL << 32)
 #endif
 
-/* Make sure we only define these if the kernel header doesn't.  */
-#ifndef GCS_MAGIC
+#ifndef HAVE_STRUCT_USER_GCS
 
 /* GCS state (NT_ARM_GCS).  */
 
@@ -39,6 +38,9 @@ struct user_gcs
   uint64_t gcspr_el0;
 };
 
-#endif /* GCS_MAGIC */
+#endif /* HAVE_STRUCT_USER_GCS */
+
+/* The GCS regset consists of 3 64-bit registers.  */
+#define AARCH64_LINUX_SIZEOF_GCS_REGSET (3 * 8)
 
 #endif /* GDB_ARCH_AARCH64_GCS_LINUX_H */
diff --git a/gdbsupport/config.in b/gdbsupport/config.in
index 0beacf22c05..2957ee0f030 100644
--- a/gdbsupport/config.in
+++ b/gdbsupport/config.in
@@ -271,6 +271,9 @@
 /* Define to 1 if `st_blocks' is a member of `struct stat'. */
 #undef HAVE_STRUCT_STAT_ST_BLOCKS
 
+/* Define to 1 if your system has struct user_gcs. */
+#undef HAVE_STRUCT_USER_GCS
+
 /* Define to 1 if you have the <sys/param.h> header file. */
 #undef HAVE_SYS_PARAM_H
 
diff --git a/gdbsupport/configure b/gdbsupport/configure
index 133ddfa7f6c..66135791aa5 100755
--- a/gdbsupport/configure
+++ b/gdbsupport/configure
@@ -14307,6 +14307,42 @@ ac_compiler_gnu=$ac_cv_c_compiler_gnu
 
 
 
+# Check for `struct user_gcs`
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for struct user_gcs" >&5
+$as_echo_n "checking for struct user_gcs... " >&6; }
+if ${gdb_cv_struct_user_gcs+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+#include <sys/ptrace.h>
+	 #include <asm/ptrace.h>
+int
+main ()
+{
+struct user_gcs u;
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+  gdb_cv_struct_user_gcs=yes
+else
+  gdb_cv_struct_user_gcs=no
+
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $gdb_cv_struct_user_gcs" >&5
+$as_echo "$gdb_cv_struct_user_gcs" >&6; }
+if test "$gdb_cv_struct_user_gcs" = yes; then
+
+$as_echo "#define HAVE_STRUCT_USER_GCS 1" >>confdefs.h
+
+fi
+
 # Set the 'development' global.
 . $srcdir/../bfd/development.sh
 
diff --git a/gdbsupport/configure.ac b/gdbsupport/configure.ac
index b7ccfabd6c6..d3b4c05daeb 100644
--- a/gdbsupport/configure.ac
+++ b/gdbsupport/configure.ac
@@ -68,6 +68,25 @@ GDB_AC_PTRACE
 AM_GDB_COMPILER_TYPE
 AM_GDB_WARNINGS
 
+# Check for `struct user_gcs`
+AC_CACHE_CHECK(
+  [for struct user_gcs],
+  [gdb_cv_struct_user_gcs],
+  [AC_COMPILE_IFELSE(
+     [AC_LANG_PROGRAM(
+	[#include <sys/ptrace.h>
+	 #include <asm/ptrace.h>],
+	[struct user_gcs u;]
+      )],
+     [gdb_cv_struct_user_gcs=yes],
+     [gdb_cv_struct_user_gcs=no]
+  )]
+)
+if test "$gdb_cv_struct_user_gcs" = yes; then
+  AC_DEFINE(HAVE_STRUCT_USER_GCS, 1,
+	    [Define to 1 if your system has struct user_gcs.])
+fi
+
 # Set the 'development' global.
 . $srcdir/../bfd/development.sh