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Re: [PATCH for 7.2] Fix broken configure with -Wunused-parameter

From: Stefan Weil
Subject: Re: [PATCH for 7.2] Fix broken configure with -Wunused-parameter
Date: Thu, 3 Nov 2022 13:08:14 +0100
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Am 03.11.22 um 12:48 schrieb Peter Maydell:

On Wed, 2 Nov 2022 at 20:24, Stefan Weil via <qemu-devel@nongnu.org> wrote:
The configure script fails because it tries to compile small C programs
with a main function which is declared with arguments argc and argv
although those arguments are unused.

Running `configure -extra-cflags=-Wunused-parameter` triggers the problem.
configure for a native build does abort but shows the error in config.log.
A cross build configure for Windows with Debian stable aborts with an

Avoiding unused arguments fixes this.

Signed-off-by: Stefan Weil <sw@weilnetz.de>

See https://gitlab.com/qemu-project/qemu/-/issues/1295.

I noticed the problem because I often compile with -Wextra.


  configure | 7 ++++---
  1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/configure b/configure
index 4275f5419f..1106c04fea 100755
--- a/configure
+++ b/configure
@@ -1258,6 +1258,7 @@ if test "$stack_protector" != "no"; then
    cat > $TMPC << EOF
  int main(int argc, char *argv[])
+    (void)argc;
I'm not a huge fan of this syntax, and it doesn't match the way
we deal with "argument is unused" elsewhere in the codebase
(where we either don't care about it or else use the GCC 'unused'
attribute hidden behind the glib G_GNUC_UNUSED macro).

Any other variant is also fine for me, for example "using" argc by a "return argc == 0;" instead of "return 0;". Would that be better? If there is an accepted variant, I can either send a v2 patch, or maybe such a trivial change can be applied when merging.

I am surprised that this didn't get caught by the check in
do_compiler_werror(), which is supposed to report "this
configure test passed without -Werror but failed with
-Werror, so configure is probably buggy.". That's what's
supposed to catch "your compiler warns on stuff our doesn't
in the test case programs".

If you're building with --disable-werror then configure
should be OK anyway. This is probably a good idea if you want
to build with extra warning arguments in --extra-cflags.
If it doesn't work right even with --disable-werror that's
also something we should investigate.

Cross builds for Windows fail with and without --disable-werror. See also my bug report https://gitlab.com/qemu-project/qemu/-/issues/1295.

You are right that this is strange and should be investigated, especially because native builds don't fail like that.

      char arr[64], *p = arr, *c = argv[0];
      while (*c) {
          *p++ = *c++;
@@ -1607,7 +1608,7 @@ fi

  if test "$safe_stack" = "yes"; then
  cat > $TMPC << EOF
-int main(int argc, char *argv[])
+int main(void)
  #if ! __has_feature(safe_stack)
  #error SafeStack Disabled
@@ -1629,7 +1630,7 @@ EOF
  cat > $TMPC << EOF
-int main(int argc, char *argv[])
+int main(void)
  #if defined(__has_feature)
  #if __has_feature(safe_stack)
@@ -1675,7 +1676,7 @@ static const int Z = 1;
  #define TAUT(X) ((X) == Z)
  #define PAREN(X, Y) (X == Y)
  #define ID(X) (X)
-int main(int argc, char *argv[])
+int main(void)
      int x = 0, y = 0;
      x = ID(x);
No objection to the cases where we can pass "void", that's
a neater way to write the test anyway.

-- PMM

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