Re: [PATCH v3 02/11] tools/nolibc: add new crt.h with _start_c

On 2023-07-14 13:58:13+0800, Zhangjin Wu wrote:

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Which one do you prefer? the one with local variables may be more readable (not that much), the one with global variables has smaller text size (and therefore smaller memory footprint).

The one with local variables. But not by much.

BTW, just found an arch-<ARCH>.h bug with -O0, seems the 'optimize("omit-frame-pointer")' attribute not really work as expected with -O0. It uses frame pointer for _start eventually and breaks the stack pointer variable (a push 'rbp' inserted at the begging of _start, so, the real rsp has an offset), so, therefore, it is not able to get the right argc, argv, environ and _auxv with -O0 currently. A solution is reverting _start to pure assembly.

For the above tests, I manually reverted the arch-x86_64.h to:

__asm__(
        ".text\n"
        ".weak _start\n"
        "_start:\n"
#ifdef _NOLIBC_STACKPROTECTOR
        "call __stack_chk_init\n" /* initialize stack protector                      */
#endif
        "xor  %ebp, %ebp\n"       /* zero the stack frame                            */
        "mov  %rsp, %rdi\n"       /* save stack pointer to %rdi, as arg1 of _start_c */
        "and  $-16, %rsp\n"       /* %rsp must be 16-byte aligned before call        */
        "call _start_c\n"         /* transfer to c runtime                           */
        "hlt\n"                   /* ensure it does not return                       */
);

'man gcc' shows:

Most optimizations are completely disabled at -O0 or if an -O level is not set on the command line, even if individual optimization flags are specified.

To want -O0 work again, since now we have C _start_c, is it ok for us to revert the commit 7f8548589661 ("tools/nolibc: make compiler and assembler agree on the section around _start") and the later __no_stack_protector changes?

This commit explicitly mentions being tested with -O0 on x86_64. I was also not able to reproduce the issue.

Before doing any reverts I think some more investigation is in order. Can you provide exact reproduction steps?

At the same time, to verify such issues, as Thomas suggested, in this series, we may need to add more startup tests to verify argc, argv, environ, _auxv, do we need to add a standalone run_startup (or run_crt) test entry just like run_syscall? or, let's simply add more in the run_stdlib, like the environ test added by Thomas. seems, the argc test is necessary one currently missing (argc

...

= 1):

CASE_TEST(argc);               EXPECT_GE(1, test_argc, 1); break;

As we summarized before, the related test cases are:

argv0:

CASE_TEST(chmod_argv0);       EXPECT_SYSZR(1, chmod(test_argv0, 0555)); break;
CASE_TEST(chroot_exe);        EXPECT_SYSER(1, chroot(test_argv0), -1, ENOTDIR); break;

environ:

CASE_TEST(chdir_root);        EXPECT_SYSZR(1, chdir("/")); chdir(getenv("PWD")); break;
CASE_TEST(environ);            EXPECT_PTREQ(1, environ, test_envp); break;
CASE_TEST(getenv_TERM);        EXPECT_STRNZ(1, getenv("TERM")); break;
CASE_TEST(getenv_blah);        EXPECT_STRZR(1, getenv("blah")); break;

auxv:

CASE_TEST(getpagesize);       EXPECT_SYSZR(1, test_getpagesize()); break;

The above tests are in different test group and are not aimed to startup test, we'd better add a run_startup (or run_crt) test group before any other tests, it is a requiremnt of the others, we at least have these ones:

+int run_startup(int min, int max)
+{
+       int test;
+       int tmp;
+       int ret = 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.
+                */
+               switch (test + __LINE__ + 1) {
+               CASE_TEST(argc);               EXPECT_GE(1, test_argc, 1); break;
+               CASE_TEST(argv_addr);          EXPECT_PTRNZ(1, test_argv); break;
+               CASE_TEST(argv_total);         EXPECT_EQ(1, environ - test_argv - 1, test_argc); break;
+               CASE_TEST(argv0_addr);         EXPECT_PTRNZ(1, argv0); break;
+               CASE_TEST(argv0_str);          EXPECT_STRNZ(1, argv0); break;
+               CASE_TEST(argv0_len);          EXPECT_GE(1, strlen(argv0), 1); break;
+               CASE_TEST(environ_addr);       EXPECT_PTRNZ(1, environ); break;
+               CASE_TEST(environ_envp);       EXPECT_PTREQ(1, environ, test_envp); break;
+               CASE_TEST(environ_total);      EXPECT_GE(1, (void *)_auxv - (void *)environ - 1, 1); break;
+               CASE_TEST(_auxv_addr);         EXPECT_PTRNZ(1, _auxv); break;
+               case __LINE__:
+                       return ret; /* must be last */
+               /* note: do not set any defaults so as to permit holes above */
+               }
+       }
+       return ret;
+}

Any more?

My original idea was to have tests that exec /proc/self/exe or argv0. This way we can actually pass and validate arbitrary argc, argv and environ values.

But looking at your list, that should be enough.

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