* Optimization auto-setting _FORTIFY_SOURCE ??
@ 2023-01-29 23:05 Patrick Herbst
2023-01-30 4:23 ` Xi Ruoyao
0 siblings, 1 reply; 3+ messages in thread
From: Patrick Herbst @ 2023-01-29 23:05 UTC (permalink / raw)
To: gcc-help
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?
Thanks!
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Optimization auto-setting _FORTIFY_SOURCE ??
2023-01-29 23:05 Optimization auto-setting _FORTIFY_SOURCE ?? Patrick Herbst
@ 2023-01-30 4:23 ` Xi Ruoyao
2023-01-30 4:57 ` LIU Hao
0 siblings, 1 reply; 3+ messages in thread
From: Xi Ruoyao @ 2023-01-30 4:23 UTC (permalink / raw)
To: Patrick Herbst; +Cc: gcc-help
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.
--
Xi Ruoyao <xry111@xry111.site>
School of Aerospace Science and Technology, Xidian University
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Optimization auto-setting _FORTIFY_SOURCE ??
2023-01-30 4:23 ` Xi Ruoyao
@ 2023-01-30 4:57 ` LIU Hao
0 siblings, 0 replies; 3+ messages in thread
From: LIU Hao @ 2023-01-30 4:57 UTC (permalink / raw)
To: Xi Ruoyao, Patrick Herbst; +Cc: gcc-help
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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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^ permalink raw reply [flat|nested] 3+ messages in thread
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2023-01-29 23:05 Optimization auto-setting _FORTIFY_SOURCE ?? Patrick Herbst
2023-01-30 4:23 ` Xi Ruoyao
2023-01-30 4:57 ` LIU Hao
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