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Date: Sun, 30 Jan 2022 20:56:40 +0200 From: Andy Shevchenko <andy.shevchenko@...il.com> To: Kees Cook <keescook@...omium.org> Cc: Geert Uytterhoeven <geert@...ux-m68k.org>, Peter Rosin <peda@...ntia.se>, Andy Shevchenko <andy@...nel.org>, Matteo Croce <mcroce@...rosoft.com>, Nathan Chancellor <nathan@...nel.org>, Nick Desaulniers <ndesaulniers@...gle.com>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, llvm@...ts.linux.dev, linux-hardening@...r.kernel.org Subject: Re: [PATCH] lib/test_string.c: Add test for strlen() On Sun, Jan 30, 2022 at 8:36 PM Kees Cook <keescook@...omium.org> wrote: > > Add a simple test for strlen() functionality, including using it as a > constant expression. ... > +/* > + * Unlike many other string functions, strlen() can be used in > + * static initializers when string lengths are known at compile > + * time. (i.e. Under these conditions, strlen() is a constant > + * expression.) Make sure it can be used this way. > + */ > +static const int strlen_ce = strlen("tada, a constant expression"); So, the compiler will replace this by a constant and then eliminate the condition completely from the code. Did I understand this correctly? > +static __init int strlen_selftest(void) > +{ > + /* String length ruler: 123456789012345 */ > + static const char normal[] = "I am normal"; > + static const char *ptr = "where do I go?"; > + static const char trailing[] = "hidden NULLs\0\0\0"; > + static const char leading[] = "\0\0hidden text"; > + > + if (strlen(normal) != 11) > + return 0x100001; > + if (strlen(ptr++) != 14) > + return 0x100002; > + if (strlen(ptr++) != 13) > + return 0x100003; > + if (strlen(trailing) != 12) > + return 0x100004; > + if (strlen(leading) != 0) > + return 0x100005; > + if (strlen_ce != 27) > + return 0x100006; ...so this part won't ever appear in the assembly (assuming -O2). Same to the rest? If so, why is this not a part of the compiler tests? > + return 0; > +} -- With Best Regards, Andy Shevchenko
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