Re: [Xen-devel] [PATCH v3 14/16] x86/boot: implement early command line parser in C

[Daniel Kiper <daniel.kiper@xxxxxxxxxx>]

On Wed, May 25, 2016 at 04:33:54AM -0600, Jan Beulich wrote:
> >>> On 15.04.16 at 14:33, <daniel.kiper@xxxxxxxxxx> wrote:
> > --- a/xen/arch/x86/boot/build32.lds
> > +++ b/xen/arch/x86/boot/build32.lds
> > @@ -25,6 +25,7 @@ SECTIONS
> >          *(.text)
> >          *(.text.*)
> >          *(.rodata)
> > +        *(.rodata.*)
> >    }
>
> Interesting - didn't you say you don't want this for now?

Yep, however, I also said that we should add "*(.rodata.*)"
if it is needed. And it is needed here.

> > --- /dev/null
> > +++ b/xen/arch/x86/boot/cmdline.c
> > @@ -0,0 +1,357 @@
> > +/*
> > + * Copyright (c) 2015, 2016 Oracle and/or its affiliates. All rights 
> > reserved.
> > + *      Daniel Kiper <daniel.kiper@xxxxxxxxxx>
> > + *
> > + * This program is free software; you can redistribute it and/or modify
> > + * it under the terms of the GNU General Public License as published by
> > + * the Free Software Foundation; either version 2 of the License, or
> > + * (at your option) any later version.
> > + *
> > + * This program is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> > + * GNU General Public License for more details.
> > + *
> > + * You should have received a copy of the GNU General Public License along
> > + * with this program.  If not, see <http://www.gnu.org/licenses/>.
> > + *
> > + * strlen(), strncmp(), strspn() and strcspn() were copied from
> > + * Linux kernel source (linux/lib/string.c).
>
> Any reason you can't just #include ".../common/string.c" here?

I am confused. Sometimes you request to reduce number of such strange
includes and sometimes you ask me to do something contrary? So, what
is the rule behind these requests?

Additionally, there is a chance that final xen ELF file will be
unnecessary larger because it will contain unused functions. Wait,
maybe there is a linker option which allows us to remove unreferenced
objects from final output.

> > +/*
> > + * Space and TAB are obvious delimiters. However, I am
> > + * adding "\n" and "\r" here too. Just in case when
> > + * crazy bootloader/user put them somewhere.
> > + */
> > +#define DELIM_CHARS                " \n\r\t"
> > +#define DELIM_CHARS_COMMA  DELIM_CHARS ","
>
> static const char[] variables (or really just one, with the comma put
> first and the non-comma variant indexing into that variable by 1)?

OK.

> > +#define __packed   __attribute__((__packed__))
>
> No way to include compiler.h here?

Ditto.

> > +/*
> > + * Compiler is not able to optimize regular strlen()
> > + * if argument is well known string during build.
> > + * Hence, introduce optimized strlen_opt().
> > + */
> > +#define strlen_opt(s) (sizeof(s) - 1)
>
> Do we really care in this code?

Not to strongly but why not?

> > +/* Keep in sync with trampoline.S:early_boot_opts label! */
> > +typedef struct __packed {
> > +    u8 skip_realmode;
> > +    u8 opt_edd;
> > +    u8 opt_edid;
> > +    u16 boot_vid_mode;
> > +    u16 vesa_width;
> > +    u16 vesa_height;
> > +    u16 vesa_depth;
> > +} early_boot_opts_t;
>
> This "keeping in sync" should be automated in some way, e.g. via
> a new header and suitable macroization.

OK.

> > +static int strtoi(const char *s, const char *stop, const char **next)
> > +{
> > +    int base = 10, i, ores = 0, res = 0;
>
> You don't even handle a '-' on the numbers here, so all the variables

Yep, however, ...

> and the function return type should be unsigned int afaict. And the
> function name perhaps be strtoui().

... we return -1 in case of error.

> > +    if ( *s == '0' )
> > +      base = (tolower(*++s) == 'x') ? (++s, 16) : 8;
> > +
> > +    for ( ; *s != '\0'; ++s )
> > +    {
> > +        for ( i = 0; stop && stop[i] != '\0'; ++i )
> > +            if ( *s == stop[i] )
> > +                goto out;
>
> strchr()?

Could be.

> > +        if ( *s < '0' || (*s > '7' && base == 8) )
> > +        {
> > +            res = -1;
> > +            goto out;
> > +        }
> > +
> > +        if ( *s > '9' && (base != 16 || tolower(*s) < 'a' || tolower(*s) > 
> > 'f') )
> > +        {
> > +            res = -1;
> > +            goto out;
> > +        }
> > +
> > +        res *= base;
> > +        res += (tolower(*s) >= 'a') ? (tolower(*s) - 'a' + 10) : (*s - 
> > '0');
>
> With the four instances, how about latching tolower(*s) into a local
> variable?

Make sense.

> > +static u8 skip_realmode(const char *cmdline)
> > +{
> > +    return !!find_opt(cmdline, "no-real-mode", 0) || !!find_opt(cmdline, 
> > "tboot=", 1);
>
> The || makes the two !! pointless.
>
> Also please settle on which type you want to use for boolean
> (find_opt()'s last parameter is "int", yet here you use "u8"), and

Could be u8.

> perhaps make yourself a bool_t.

I do not think it make sense here.

> > +static void vga_parse(const char *cmdline, early_boot_opts_t *ebo)
> > +{
> > +    const char *c;
> > +    int tmp;
> > +
> > +    c = find_opt(cmdline, "vga=", 1);
> > +
> > +    if ( !c )
> > +        return;
> > +
> > +    ebo->boot_vid_mode = ASK_VGA;
> > +
> > +    if ( !strmaxcmp(c, "current", DELIM_CHARS_COMMA) )
> > +        ebo->boot_vid_mode = VIDEO_CURRENT_MODE;
> > +    else if ( !strsubcmp(c, "text-80x") )
> > +    {
> > +        c += strlen_opt("text-80x");
> > +        ebo->boot_vid_mode = rows2vmode(strtoi(c, DELIM_CHARS_COMMA, 
> > NULL));
> > +    }
> > +    else if ( !strsubcmp(c, "gfx-") )
> > +    {
> > +        tmp = strtoi(c + strlen_opt("gfx-"), "x", &c);
> > +
> > +        if ( tmp < 0 || tmp > U16_MAX )
> > +            return;
> > +
> > +        ebo->vesa_width = tmp;
> > +
> > +        /*
> > +         * Increment c outside of strtoi() because otherwise some
> > +         * compiler may complain with following message:
> > +         * warning: operation on ‘c’ may be undefined.
> > +         */
> > +        ++c;
> > +        tmp = strtoi(c, "x", &c);
>
> The comment is pointless - the operation is firmly undefined if you
> put it in the strtoi() invocation.

In terms of C spec you are right. However, it is quite surprising that older
GCC complains and newer ones do not. Should not we investigate this?

> > +        if ( tmp < 0 || tmp > U16_MAX )
> > +            return;
> > +
> > +        ebo->vesa_height = tmp;
> > +
> > +        tmp = strtoi(++c, DELIM_CHARS_COMMA, NULL);
> > +
> > +        if ( tmp < 0 || tmp > U16_MAX )
> > +            return;
> > +
> > +        ebo->vesa_depth = tmp;
> > +
> > +        ebo->boot_vid_mode = VIDEO_VESA_BY_SIZE;
>
> I realize this is reflecting original behavior, but now that you do it in
> C, please leverage that fact and defer storing width and height until
> you know the entire option was good.

OK.

> > --- a/xen/arch/x86/boot/head.S
> > +++ b/xen/arch/x86/boot/head.S
> > @@ -436,8 +436,24 @@ trampoline_setup:
> >          cmp     $sym_phys(__trampoline_seg_stop),%edi
> >          jb      1b
> >
> > +        /* Do not parse command line on EFI platform here. */
> > +        cmpb    $1,sym_phys(skip_realmode)
> > +        je      1f
>
> Doesn't this belong in an earlier patch? It certainly doesn't get
> moved here from cmdline.S.

Potentially.

> > +        /* Bail if there is no command line to parse. */
> > +        mov     sym_phys(multiboot_ptr),%ebx
> > +        testl   $MBI_CMDLINE,MB_flags(%ebx)
> > +        jz      1f
> > +
> > +        cmpl    $0,MB_cmdline(%ebx)
> > +        jz      1f
>
> Any reason not to leave at least this check to the C code?

OK.

> > +        pushl   $sym_phys(early_boot_opts)
> > +        pushl   MB_cmdline(%ebx)
> >          call    cmdline_parse_early
> > +        add     $8,%esp             /* Remove cmdline_parse_early() args 
> > from stack. */
>
> I don't think such a comment is really useful (seems like I overlooked
> a similar one in an earlier patch, on the reloc() invocation).

This thing is quite obvious but I do not think that this comment hurts.

Daniel

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