From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on gnuweeb.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=5.0 tests=ALL_TRUSTED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,NO_DNS_FOR_FROM,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.6 Received: from localhost.localdomain (unknown [182.253.88.132]) by gnuweeb.org (Postfix) with ESMTPSA id 2D9008198C; Thu, 22 Dec 2022 13:46:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gnuweeb.org; s=default; t=1671716795; bh=LDvvlYG5c3kSYFfaFM3BhTe68E9j08MA7aHXPWHcB34=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=REmOUL+Gt9v9/UcyoayCxyiTm2KQnM0KqX0U+jR1jkbTKzODCcnGrQtTInpD40gNz byu6y1C/Ws3HTo7Yh943Gux36O0JQUj8kZ7dql0Ty0hszdATJj79bBUv8NFSfjvc31 0Vwhsc+L7NdGKBFkZikGU4TiSRu7jQ850wsVeluamCKmQKhaW4/gACkhwfWPE1z3Rj 6IDdP8e2bN2EnKneho2pQoxZWR23Juj5Mz4/GFyDeG395Dpkg78CvmsCnJTLovAjvr tMJaChh895nhLGuAEh+ykUP8exFamhox/dRqebm6OKJrd5DqIXHjShwCqYeZ62YE+L JKUT4Nv+8tN7A== From: Ammar Faizi To: Willy Tarreau Cc: Ammar Faizi , Shuah Khan , "Paul E. McKenney" , Gilang Fachrezy , VNLX Kernel Department , Alviro Iskandar Setiawan , Kanna Scarlet , Muhammad Rizki , GNU/Weeb Mailing List , Linux Kernel Mailing List , Linux Kselftest Mailing List Subject: Re: [RFC PATCH v1 0/8] nolibc signal handling support Date: Thu, 22 Dec 2022 20:46:15 +0700 Message-Id: <20221222134615.3535422-1-ammar.faizi@intel.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20221222043452.GB29086@1wt.eu> References: <20221222035134.3467659-1-ammar.faizi@intel.com> <20221222043452.GB29086@1wt.eu> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit List-Id: On Thu, 22 Dec 2022 05:34:52 +0100, Willy Tarreau wrote: > This one relies on /proc/self/auxv, but we'll quickly run into a > chicken-and-egg situation given that nolibc is used by init programs > that mount /proc. Instead I think that we should modify the _start > code to retrieve the auxv at startup and store it somewhere. This > "somewhere" is not yet defined, but I'm thinking that it could > deserve reserving some room in the stack to store some nolibc-defined > information (possibly even a copy of a pointer to environ and/or errno) > and figure a reliable and simple way to access this. Note that one way > could also be to know that it's after the NULL that follows envp, and > to start from environ. In fact there are plenty of ways and we just > need to decide what's the least ugly. But once we have access to the > auxv from the process, then we could implement a getauxval() function > to retrieve the information you need for getpagesize(). Thanks for the great feedback! I agree with following the @envp pointer to get the auxv. I was trying to wire up a new function '__start' (with double underscores) written in C that accepts @argc, @argv and @envp. Then it calls 'main'. Then we call '__start' instead of 'main' from '_start'. This way, we can arrange nolibc-defined data without touching Assembly much in '__start' (before main). But then I noticed that it wouldn't work because we may have users who define the 'main' function differently, e.g.: int main(void); int main(int argc, char **argv); int main(int argc, char **argv, char **envp); So '__start' can't call main. We still need to call the main from the inline Assembly (from '_start'). Just a quick dirty patch to get getauxval() works on x86-64 below. This needs more work, but at least something like this for starting: $ ./nolibc-test Running test 'syscall' AT_SYSINFO_EHDR = 140737354125312 AT_HWCAP = 3219913727 AT_PAGESZ = 4096 AT_CLKTCK = 100 AT_PHDR = 4194368 AT_PHENT = 56 AT_PHNUM = 9 AT_BASE = 0 AT_FLAGS = 0 AT_ENTRY = 4199128 AT_UID = 0 AT_EUID = 0 AT_GID = 0 AT_EGID = 0 AT_SECURE = 0 AT_RANDOM = 140737488349065 AT_EXECFN = 140737488351210 AT_PLATFORM = 140737488349081 I'll probably only spare more intensive time on this after the holiday season ends. I still check in email, but the activity will be sparse. Signed-off-by: [Do not commit] --- base-commit: caf5c36025ec9395c8d7c78957b016a284812d23 ("srcu: Update comment after the index flip") diff --git a/tools/include/nolibc/arch-x86_64.h b/tools/include/nolibc/arch-x86_64.h index 0e1e9eb8545d..5ee945370ff5 100644 --- a/tools/include/nolibc/arch-x86_64.h +++ b/tools/include/nolibc/arch-x86_64.h @@ -199,17 +199,49 @@ struct sys_stat_struct { */ __asm__ (".section .text\n" ".weak _start\n" "_start:\n" "pop %rdi\n" // argc (first arg, %rdi) "mov %rsp, %rsi\n" // argv[] (second arg, %rsi) "lea 8(%rsi,%rdi,8),%rdx\n" // then a NULL then envp (third arg, %rdx) "xor %ebp, %ebp\n" // zero the stack frame "and $-16, %rsp\n" // x86 ABI : esp must be 16-byte aligned before call + "push %rdi\n" // Save argc + "push %rsi\n" // Save arg + "push %rdx\n" // Save envp. + "push %rcx\n" // Keep the 16-byte alignment + "call __start\n" // Save environ and auxv + "pop %rcx\n" // Restore alignment + "pop %rdx\n" // Restore envp + "pop %rsi\n" // Restore argv + "pop %rdi\n" // Restore argc "call main\n" // main() returns the status code, we'll exit with it. "mov %eax, %edi\n" // retrieve exit code (32 bit) "mov $60, %eax\n" // NR_exit == 60 "syscall\n" // really exit "hlt\n" // ensure it does not return ""); +struct __nolibc_internal { + char **envp; + unsigned long *auxv; +}; + +static struct __nolibc_internal __nolibc_internal; + +/* + * Mark this __used__ to avoid being optimized away. + * Reason: Called from inline Assembly. + */ +static __attribute__((__used__)) +void __start(int argc, char **argv, char **envp) +{ + char **p = envp; + + while (*p) + p++; + + __nolibc_internal.auxv = (unsigned long *)++p; + __nolibc_internal.envp = envp; +} + #endif // _NOLIBC_ARCH_X86_64_H diff --git a/tools/include/nolibc/sys.h b/tools/include/nolibc/sys.h index 3db1dd8c74ee..04bff724e056 100644 --- a/tools/include/nolibc/sys.h +++ b/tools/include/nolibc/sys.h @@ -12,18 +12,19 @@ /* system includes */ #include #include // for SIGCHLD #include #include #include #include #include +#include #include "arch.h" #include "errno.h" #include "types.h" /* Functions in this file only describe syscalls. They're declared static so * that the compiler usually decides to inline them while still being allowed * to pass a pointer to one of their instances. Each syscall exists in two @@ -379,18 +380,49 @@ int fsync(int fd) if (ret < 0) { SET_ERRNO(-ret); ret = -1; } return ret; } +/* + * On success, getauxval() returns the value corresponding to type. + * If type is not found, 0 is returned. + * + * unsigned long getauxval(unsigned long type); + */ + +static __attribute__((unused)) +unsigned long getauxval(unsigned long type) +{ + unsigned long *auxv = __nolibc_internal.auxv; + + if (__builtin_expect(!auxv, 0)) + return 0; + + while (1) { + if (!auxv[0] && !auxv[1]) + /* + * We've reached the end of auxv. + */ + return 0; + + if (auxv[0] == type) + return auxv[1]; + + auxv += 2; + } + __builtin_unreachable(); +} + + /* * int getdents64(int fd, struct linux_dirent64 *dirp, int count); */ static __attribute__((unused)) int sys_getdents64(int fd, struct linux_dirent64 *dirp, int count) { return my_syscall3(__NR_getdents64, fd, dirp, count); } diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c index f14f5076fb6d..bca29a952c69 100644 --- a/tools/testing/selftests/nolibc/nolibc-test.c +++ b/tools/testing/selftests/nolibc/nolibc-test.c @@ -436,30 +436,60 @@ int test_getdents64(const char *dir) ret = getdents64(fd, (void *)buffer, sizeof(buffer)); err = errno; close(fd); errno = err; return ret; } +static void test_getauxval(void) +{ + #define PRINT_AUXVAL(KEY) \ + do { \ + printf(#KEY " = %lu\n", getauxval(KEY)); \ + } while (0) + + PRINT_AUXVAL(AT_SYSINFO_EHDR); + PRINT_AUXVAL(AT_HWCAP); + PRINT_AUXVAL(AT_PAGESZ); + PRINT_AUXVAL(AT_CLKTCK); + PRINT_AUXVAL(AT_PHDR); + PRINT_AUXVAL(AT_PHENT); + PRINT_AUXVAL(AT_PHNUM); + PRINT_AUXVAL(AT_BASE); + PRINT_AUXVAL(AT_FLAGS); + PRINT_AUXVAL(AT_ENTRY); + PRINT_AUXVAL(AT_UID); + PRINT_AUXVAL(AT_EUID); + PRINT_AUXVAL(AT_GID); + PRINT_AUXVAL(AT_EGID); + PRINT_AUXVAL(AT_SECURE); + PRINT_AUXVAL(AT_RANDOM); + PRINT_AUXVAL(AT_EXECFN); + PRINT_AUXVAL(AT_PLATFORM); + exit(0); +} + /* Run syscall tests between IDs and . * Return 0 on success, non-zero on failure. */ int run_syscall(int min, int max) { struct stat stat_buf; int proc; int test; int tmp; int ret = 0; void *p1, *p2; + test_getauxval(); + /* indicates whether or not /proc is mounted */ proc = stat("/proc", &stat_buf) == 0; for (test = min; test >= 0 && test <= max; test++) { int llen = 0; // line length /* avoid leaving empty lines below, this will insert holes into * test numbers. */ -- Ammar Faizi