linux-kernel - Re: [PATCH v3 9/9] selftests/sgx: Specify freestanding environment for enclave compilation

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Date:   Wed, 23 Aug 2023 20:31:32 +0300
From:   "Jarkko Sakkinen" <jarkko@...nel.org>
To:     "Jo Van Bulck" <jo.vanbulck@...kuleuven.be>, <kai.huang@...el.com>,
        <linux-sgx@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Cc:     <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH v3 9/9] selftests/sgx: Specify freestanding environment
 for enclave compilation

On Wed Aug 23, 2023 at 3:57 PM EEST, Jo Van Bulck wrote:
> On 22.08.23 12:14, Jarkko Sakkinen wrote:
> > Do you still need nostdfiles and nostartfiles with freestanding?
>
> Thanks, good question. I tested that compiling with only -ffreestanding 
> yields:
>
> /* snipped */
> /usr/local/bin/ld: 
> /usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/rcrt1.o: in 
> function `_start':
> (.text+0x24): undefined reference to `main'
> /* snipped */
>
> So we definitely still need -nostartfiles to prevent the compiler/linker 
> from introducing the standard system startup functions. However, in my 
> understanding, -nostdlib (which is what I assume you mean with 
> nostdfiles) already implies the individual options -nodefaultlibs and 
> -nostartfiles.
>
> Thus, we definitely still need -nostartfiles and I'm not 100% sure we 
> don't need -nostdlib (though it compiles fine for me with only 
> -nostartfiles). Gcc only specifies:
>
> -ffreestanding
> Assert that compilation targets a freestanding environment.  This 
> implies -fno-builtin. A freestanding environment is one in which the 
> standard library may not exist, and program startup may not necessarily 
> be at "main".
>
> Bottom line: I suggest to keep -nostdlib to be sure and remove 
> -nostartfiles (as it is redundant). I'll include this in the next  patch 
> iteration.
>
> Best,
> Jo

OK, cool, sounds like plan.

BR, Jarkko