Issue in man page syscall.2

Issue in man page syscall.2

[Helge Kreutzmann]

Without further ado, the following was found:

Issue:    of 0 → of I<r0>?

"Since the offset argument is 64 bits, and the first argument (I<fd>)  is "
"passed in I<r0>, the caller must manually split and align the 64-bit value "
"so that it is passed in the I<r2>/I<r3> register pair.  That means inserting "
"a dummy value into I<r1> (the second argument of 0).  Care also must be "
"taken so that the split follows endian conventions (according to the C ABI "
"for the platform)."

Re: Issue in man page syscall.2

[Alejandro Colomar]

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Hi Helge,

On 12/4/22 10:07, Helge Kreutzmann wrote:
> Without further ado, the following was found:
> 
> Issue:    of 0 → of I<r0>?
> 
> "Since the offset argument is 64 bits, and the first argument (I<fd>)  is"
> "passed in I<r0>, the caller must manually split and align the 64-bit value"
> "so that it is passed in the I<r2>/I<r3> register pair.  That means inserting"
> "a dummy value into I<r1> (the second argument of 0).  Care also must be"
> "taken so that the split follows endian conventions (according to the C ABI"
> "for the platform)."

The report is invalid:


            syscall(SYS_readahead, fd, 0,
                    (unsigned int) (offset & 0xFFFFFFFF),
                    (unsigned int) (offset >> 32),
                    count);

        Since the offset argument is 64 bits, and the first argu‐
        ment (fd) is passed in r0, the caller must manually split
        and align the 64‐bit value so that it is  passed  in  the
        r2/r3  register pair.  That means inserting a dummy value
        into r1 (the second argument of 0).  Care  also  must  be
        taken  so  that the split follows endian conventions (ac‐
        cording to the C ABI for the platform).

It's saying that the second argument in the call above is the value 0.

Cheers,

Alex


-- 
<http://www.alejandro-colomar.es/>

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Re: Issue in man page syscall.2

[Helge Kreutzmann]

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Hello Alejandro,
On Sun, Dec 04, 2022 at 09:00:20PM +0100, Alejandro Colomar wrote:
> On 12/4/22 10:07, Helge Kreutzmann wrote:
> > Without further ado, the following was found:
> > 
> > Issue:    of 0 → of I<r0>?
> > 
> > "Since the offset argument is 64 bits, and the first argument (I<fd>)  is"
> > "passed in I<r0>, the caller must manually split and align the 64-bit value"
> > "so that it is passed in the I<r2>/I<r3> register pair.  That means inserting"
> > "a dummy value into I<r1> (the second argument of 0).  Care also must be"
> > "taken so that the split follows endian conventions (according to the C ABI"
> > "for the platform)."
> 
> The report is invalid:
> 
> 
>            syscall(SYS_readahead, fd, 0,
>                    (unsigned int) (offset & 0xFFFFFFFF),
>                    (unsigned int) (offset >> 32),
>                    count);
> 
>        Since the offset argument is 64 bits, and the first argu‐
>        ment (fd) is passed in r0, the caller must manually split
>        and align the 64‐bit value so that it is  passed  in  the
>        r2/r3  register pair.  That means inserting a dummy value
>        into r1 (the second argument of 0).  Care  also  must  be
>        taken  so  that the split follows endian conventions (ac‐
>        cording to the C ABI for the platform).
> 
> It's saying that the second argument in the call above is the value 0.

Noted and thanks for the clarification!

Greetings

        Helge

-- 
      Dr. Helge Kreutzmann                     debian@helgefjell.de
           Dipl.-Phys.                   http://www.helgefjell.de/debian.php
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