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Re: [PATCH] configure: Improve alias attribute check


From: Thomas Huth
Subject: Re: [PATCH] configure: Improve alias attribute check
Date: Sat, 20 Mar 2021 05:48:32 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0

On 20/03/2021 05.27, Gavin Shan wrote:
It's still possible that the wrong value is returned from the alias
of variable even if the program can be compiled without issue. This
improves the check by executing the binary to check the result.

If alias attribute can't be working properly, the @target_page in
exec-vary.c will always return zeroes when we have the following gcc
version.

   # gcc --version
   gcc (GCC) 11.0.0 20210210 (Red Hat 11.0.0-0)

This abstracts the code from exec-vary.c and use it as indicator to
enable gcc alias attribute or not.

Signed-off-by: Gavin Shan <gshan@redhat.com>
---
  configure | 34 ++++++++++++++++++++++++++++++----
  1 file changed, 30 insertions(+), 4 deletions(-)

diff --git a/configure b/configure
index f7d022a5db..8321f380d5 100755
--- a/configure
+++ b/configure
@@ -75,6 +75,7 @@ fi
TMPB="qemu-conf"
  TMPC="${TMPDIR1}/${TMPB}.c"
+TMPC_B="${TMPDIR1}/${TMPB}_b.c"
  TMPO="${TMPDIR1}/${TMPB}.o"
  TMPCXX="${TMPDIR1}/${TMPB}.cxx"
  TMPE="${TMPDIR1}/${TMPB}.exe"
@@ -4878,13 +4879,38 @@ fi
attralias=no
  cat > $TMPC << EOF
-int x = 1;
+static int x;
  extern const int y __attribute__((alias("x")));
-int main(void) { return 0; }
+extern int read_y(void);
+void write_x(int val);
+
+void write_x(int val)
+{
+    x = val;
+}
+
+int main(void)
+{
+    return read_y();
+}
  EOF
-if compile_prog "" "" ; then
-    attralias=yes
+cat > $TMPC_B << EOF
+extern const int y;
+extern void write_x(int val);
+int read_y(void);
+
+int read_y(void)
+{
+     write_x(1);
+     return y;
+}
+EOF
+
+TMPC+=" ${TMPC_B}"
+if compile_prog "" "" && ! $TMPE; then

What about cross-compiling? Running an executable won't work if QEMU gets cross-compiled...

 Thomas




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