[PATCH v2 2/2] GDB: aarch64-linux: Fix build failure on musl systems

[Thiago Jung Bauermann <thiago.bauermann@linaro.org>]

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:23:
  /home/bauermann/src/binutils-gdb/gdbserver/../gdb/nat/aarch64-linux.h:123:8: error: redefinition of 'struct user_gcs'
    123 | struct user_gcs
        |        ^~~~~~~~
  In file included from /home/bauermann/src/binutils-gdb/gdbserver/../gdb/nat/aarch64-linux.h:24:
  /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-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.

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.

Co-authored-by: Chris Packham <judge.packham@gmail.com>
---
 gdb/nat/aarch64-linux.h |  5 ++---
 gdbsupport/config.in    |  3 +++
 gdbsupport/configure    | 36 ++++++++++++++++++++++++++++++++++++
 gdbsupport/configure.ac | 19 +++++++++++++++++++
 4 files changed, 60 insertions(+), 3 deletions(-)

diff --git a/gdb/nat/aarch64-linux.h b/gdb/nat/aarch64-linux.h
index f7c09aa112bf..0f1fa093d003 100644
--- a/gdb/nat/aarch64-linux.h
+++ b/gdb/nat/aarch64-linux.h
@@ -115,8 +115,7 @@ typedef struct compat_siginfo
 #define cpt_si_band _sifields._sigpoll._band
 #define cpt_si_fd _sifields._sigpoll._fd
 
-/* 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).  */
 
@@ -127,7 +126,7 @@ struct user_gcs
   uint64_t gcspr_el0;
 };
 
-#endif /* GCS_MAGIC */
+#endif /* HAVE_STRUCT_USER_GCS */
 
 void aarch64_siginfo_from_compat_siginfo (siginfo_t *to,
 					    compat_siginfo_t *from);
diff --git a/gdbsupport/config.in b/gdbsupport/config.in
index 0beacf22c057..2957ee0f0301 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 05ad00f48c4f..584a80ef8255 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 5491b8f3f10a..6c06832f0913 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