[binutils-gdb] [gdb/build] Reimplement Wstringop-overread workaround

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=0466831f8b8980d7313bdf1922990ae7411fdf57

commit 0466831f8b8980d7313bdf1922990ae7411fdf57
Author: Tom de Vries <[email protected]>
Date:   Thu Apr 16 12:55:17 2026 +0200

    [gdb/build] Reimplement Wstringop-overread workaround
    
    While working on commit 391c4026573 ("[gdb] Simplify debuginfod_is_enabled") I
    noticed this Wstringop-overread workaround:
    ...
          url_view = url_view.substr (off);
          /* g++ 11.2.1 on s390x, g++ 11.3.1 on ppc64le and g++ 11 on
             hppa seem convinced url_view might be of SIZE_MAX length.
             And so complains because the length of an array can only
             be PTRDIFF_MAX.  */
          DIAGNOSTIC_PUSH
          DIAGNOSTIC_IGNORE_STRINGOP_OVERREAD
          off = url_view.find_first_of (' ');
          DIAGNOSTIC_POP
    ...
    
    I had difficulty understanding how the warning got triggered, and why it was
    ok to ignore it, so I investigated this and ended up filing a gcc PR [1].
    
    While doing so, I realized that this:
    ...
    -      url_view = url_view.substr (off);
    +      url_view = url_view.substr (off, PTRDIFF_MAX);
    ...
    is a simpler workaround, that:
    - is not specific to the warning and also
    - states explicitly what the assumption is we're making.
    
    I ended up using this instead to make the workaround part more minimal:
    ...
           url_view = url_view.substr (off);
    +      url_view = url_view.substr (0, PTRDIFF_MAX);
           off = url_view.find_first_of (' ');
    ...
    
    The gcc PR got closed because it's supposed to be fixed in 12.1, so the
    workaround is enabled only for g++ < 12.1.
    
    Tested on x86_64-linux.
    
    Approved-By: Tom Tromey <[email protected]>
    
    [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124879

Diff:
---
 gdb/debuginfod-support.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/gdb/debuginfod-support.c b/gdb/debuginfod-support.c
index 40b816c5a40..0d666692ff8 100644
--- a/gdb/debuginfod-support.c
+++ b/gdb/debuginfod-support.c
@@ -249,14 +249,17 @@ debuginfod_is_enabled ()
       if (off == std::string_view::npos)
 	break;
       url_view = url_view.substr (off);
-      /* g++ 11.2.1 on s390x, g++ 11.3.1 on ppc64le and g++ 11 on
-	 hppa seem convinced url_view might be of SIZE_MAX length.
-	 And so complains because the length of an array can only
-	 be PTRDIFF_MAX.  */
-      DIAGNOSTIC_PUSH
-      DIAGNOSTIC_IGNORE_STRINGOP_OVERREAD
+#if defined (__GNUC__) && !defined (__clang__)				\
+  && ((__GNUC__ <= 11) || (__GNUC__ == 12 && __GNUC_MINOR__ < 1))
+      /* With g++ 11, we encounter a Wstringop-overread in
+	 url_view.find_first_of.  G++ seems convinced url_view might be of
+	 SIZE_MAX length here.  And so complains because the length of an
+	 array can only be PTRDIFF_MAX.  Work around this by explicitly
+	 limiting the size of url_view to PTRDIFF_MAX.  This is supposed to be
+	 fixed in GCC 12.1, see PR gcc/124879.  */
+      url_view = url_view.substr (0, PTRDIFF_MAX);
+#endif
       off = url_view.find_first_of (' ');
-      DIAGNOSTIC_POP
       gdb_printf
 	(_("  <%ps>\n"),
 	 styled_string (file_name_style.style (),