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   Alan Coopersmith (alanc@fosstodon.org)'s status on Monday, 23-Sep-2024 12:11:03 JST Alan Coopersmith

   So much fun when clang optimizes out your autoconf checks:
   https://gitlab.freedesktop.org/xorg/util/macros/-/issues/4

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     Jann Horn (jann@infosec.exchange)'s status on Monday, 23-Sep-2024 12:11:03 JST Jann Horn

     in reply to

     @alanc trying to determine at build time if malloc can return NULL seems kinda unsafe anyway? like, what if the same kind of compiler optimization also applies to the code that uses the macro, or if an update to the libc changes this behavior?

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     Alan Coopersmith (alanc@fosstodon.org)'s status on Monday, 23-Sep-2024 12:11:03 JST Alan Coopersmith

     in reply to

     • Jann Horn

     @jann this is true, as is the concern that LD_PRELOADing a different malloc implementation is risky, but X11 has gotten away with it for almost 20 years now. (For the twenty years before that, it was hardcoded per-platform in the Imake config files.)

     I believe it's mostly an optimization to not have to use a malloc wrapper macro that does (size == 0 ? 1 : size) to the size argument everywhere, and that level of micro-optimization may be pointless now compared to 40 years ago.

     Haelwenn /элвэн/ :triskell: likes this.
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     Jann Horn (jann@infosec.exchange)'s status on Monday, 23-Sep-2024 12:11:22 JST Jann Horn

     in reply to

     @alanc aah, and I guess that also means it's safe if the compiler optimizes malloc(0) into NULL when the libc doesn't do that, only the other direction would break stuff...

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     Alan Coopersmith (alanc@fosstodon.org)'s status on Monday, 23-Sep-2024 12:11:22 JST Alan Coopersmith

     in reply to

     • Jann Horn

     @jann probably the safest fix is to find and fix all the code in X11 that assumes malloc(0) returns a valid pointer, such as https://gitlab.freedesktop.org/xorg/lib/libx11/-/commit/86e71472bc826ac5c850e200cb3820485b5689cf and gcc's -Walloc-zero warnings may help there, but X11 is large and full of cruft.

     Haelwenn /элвэн/ :triskell: likes this.