在 2023/1/30 12:23, Xi Ruoyao via Gcc-help 写道:
On Sun, 2023-01-29 at 18:05 -0500, Patrick Herbst via Gcc-help wrote:Using GCC 9.4, I've noticed setting -O1 will set _FORTIFY_SOURCE=2 I'm able to see this by running gcc -c -E -dM -O1 - < /dev/null | grep FORTIFY_SOURCE But running the same command without -O1 doesn't set it. Is this documented? is this expected behavior? I could not find any reference to how optimization leads to setting this macro. Any tips on where I can look, or what i'm missing to see this connection?It's because your distro hacked GCC code to define _FORTIFY_SOURCE when optimization is enabled. Vanilla GCC does not have this behavior.
For the record: Debian and Ubuntu are known distros that have `_FORTIFY_SOURCE` set when optimization is enabled. The relevant patch is here
https://sources.debian.org/src/gcc-8/8.3.0-2/debian/patches/gcc-default-fortify-source.diff/however the hunk against 'invoke.texi' is incorrect: It says `_FORTIFY_SOURCE` is enabled if optimization level 'is set to 2 or higher', but it is actually defined for any optimization level > 0.
-- Best regards, LIU Hao
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