Date: Fri, 6 Oct 2017 17:53:38 -0700 From: Andre McCurdy <armccurdy@...il.com> To: musl@...ts.openwall.com Subject: How to handle attempts to combine ARM Thumb with frame pointers? When compiling for ARM Thumb or Thumb2 with frame pointers enabled (ie -O0 or with -fno-omit-frame-pointer in CFLAGS) the frame pointer is stored in r7, which leads to build errors ("error: r7 cannot be used in asm here") whenever a syscall macro is included in a C function. It's certainly a corner case, but one which I've run into recently. Would it be worth trying to catch this combination earlier and failing from the configure script? It's not trivial to do reliably since I think detecting whether or not frame pointers are going to be used by examining CFLAGS means determining the effective optimisation level if multiple -O0, -Os, etc options are given, together with the effective outcome of potentially multiple -fno-omit-frame-pointer and -fomit-frame-pointer options. I can work on a patch for the configure script but first wanted to check what the philosophy is - should the configure script be trying to catch every possible misconfiguration?
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