On Sat, May 20, 2023 at 04:07:34PM +0200, Thomas Weißschuh wrote: > Hi Willy! > > On 2023-05-20 15:32:37+0200, Willy Tarreau wrote: > > Thomas, Zhangjin, > > > > I've merged your latest patches in my branch 20230520-nolibc-rv32+stkp2, > > which was rebased to integrate the updated commit messages and a few > > missing s-o-b from mine. Please have a look: > > > > https://git.kernel.org/pub/scm/linux/kernel/git/wtarreau/nolibc.git > > > > However, Thomas, I noticed something puzzling me. While I tested with > > gcc-9.5 (that I have here along my toolchains) I found that it would > > systematically fail: > > > > sysroot/x86/include/stackprotector.h:46:1: warning: 'no_stack_protector' attribute directive ignored [-Wattributes] > > 46 | { > > | ^ > > !!Stack smashing detected!! > > qemu: uncaught target signal 6 (Aborted) - core dumped > > 0 test(s) passed. > > > > The reason is that it doesn't support the attribute "no_stack_protector". > > Upon closer investigation, I noticed that _start() on x86_64 doens't have > > it, yet it works on more recent compilers! So I don't understand why it > > works with more recent compilers. > > _start() not having the attribute is indeed an oversight. > No idea how it worked before. No problem, I preferred to mention it anyway. > > I managed to avoid the crash by enclosing the __stack_chk_init() function > > in a #pragma GCC optimize("-fno-stack-protector") while removing the > > attribute (though Clang and more recent gcc use this attribute so we > > shouldn't completely drop it either). > > I would like to first align x86 to __attribute__((no_stack_protector)) > for uniformity and then figure out on how to make it nicer. I agree. > > I consider this non-critical as we can expect that regtests are run with > > a reasonably recent compiler version, but if in the long term we can find > > a more reliable detection for this, it would be nice. > > > > For example I found that gcc defines __SSP_ALL__ to 1 when > > -fstack-protector is used, and 2 when -fstack-protector-all is used. > > With clang, it's 1 and 3 respectively. Maybe we should use that and > > drop NOLIBC_STACKPROTECTOR, that would be one less variable to deal > > with: the code would automatically adapt to whatever cflags the user > > sets on the compiler, which is generally better. > > That sounds great! > > I explicitly looked for something like this before, dumping preprocessor > directives and comparing. > It seems the fact that my compilers enable this feature by default made > me miss it. Hmmm that's indeed possible. With -fno-stack-protector it should disappear: $ gcc -fno-stack-protector -dM -E -xc - < /dev/null |grep SSP $ gcc -fstack-protector -dM -E -xc - < /dev/null |grep SSP #define __SSP__ 1 $ gcc -fstack-protector-all -dM -E -xc - < /dev/null |grep SSP #define __SSP_ALL__ 2 $ clang -fstack-protector-all -dM -E -xc - < /dev/null |grep SSP #define __SSP_ALL__ 3 > I'll send patches. OK thanks. Just be aware that I'll be less responsive this week-end from now on. Willy
