Re: Implement standard file operation with QEMU

[casmac <climber.cui@qq.com>]

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Hello Phil,
   What I want to realize is to be able to call standard file operations (open, read, write etc) in the application program, and execute such programs in QEMU. But I am building under system mode.
   TI provide copilation toolchain and a library that provide partial functionality from libc. I am hoping to use TI's toolkit to generate object code which contains calls to hook functions, and then use QEMU's host I/O implementation to realize low-level file operation. For example:

&nbsp; &nbsp; _stream[fildes]-&gt;WRITE&nbsp; <---hook to ---&gt;&nbsp;qemu_semihosting_console_outs
&nbsp; &nbsp;Are you suggesting that this is done by TCG helpers?


best regards,
xiaolei
&nbsp;&nbsp; 





------------------ Original ------------------
From:                                                                                                                        "Philippe Mathieu-Daudé"                                                                                    <f4bug@amsat.org&gt;;
Date:&nbsp;Thu, Jul 16, 2020 03:57 PM
To:&nbsp;"casmac"<climber.cui@qq.com&gt;;"qemu-devel"<qemu-devel@nongnu.org&gt;;"Alex Bennée"<alex.bennee@linaro.org&gt;;"Laurent Vivier"<lvivier@redhat.com&gt;;"Marc-André Lureau"<marcandre.lureau@redhat.com&gt;;

Subject:&nbsp;Re: Implement standard file operation with QEMU



Hi Xiaolei,

+Laurent (user-mode)
+Alex (semihosting)
+Marc-André (chardev)

On 7/16/20 2:51 AM, casmac wrote:
&gt; Hi all,
&gt; &nbsp; I am trying to implment standard file operation (stdio) with QEMU for
&gt; DSP architecture. The manufacture (TI) provides a runtime library that
&gt; support posix standard IO, but it left the device level implmentation as
&gt; hook function calls, like in the library source , it contains 
&gt; add_device() function, and write(),read(),open() are not implemented:
&gt; 
&gt; int add_device(char&nbsp; &nbsp; &nbsp; *name,
&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; unsigned &nbsp; flags,
&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; int&nbsp; &nbsp; &nbsp; (*dopen)&nbsp; (const char *path, unsigned flags, int
&gt; foo),
&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; int&nbsp; &nbsp; &nbsp; (*dclose) (int fno),
&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; int&nbsp; &nbsp; &nbsp; (*dread)&nbsp; (int fno, char *buf, unsigned count),
&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; int&nbsp; &nbsp; &nbsp; (*dwrite) (int fno, const char *buf, unsigned
&gt; count),
&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; fpos_t &nbsp; &nbsp; (*dlseek) (int fno, fpos_t offset, int origin),
&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; int&nbsp; &nbsp; &nbsp; (*dunlink)(const char *path),
&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; int&nbsp; &nbsp; &nbsp; (*drename)(const char *old_name, const char
&gt; *new_name))
&gt; {
&gt; &nbsp;&nbsp; _DEVICE *dt;
&gt; 
&gt; &nbsp;&nbsp; strncpy(dt-&gt;name,name,8);
&gt; &nbsp;&nbsp; dt-&gt;name[8] = '\0';
&gt; &nbsp;&nbsp; dt-&gt;flags &nbsp; = flags;
&gt; &nbsp;&nbsp; dt-&gt;OPEN&nbsp; &nbsp; = dopen;
&gt; &nbsp;&nbsp; dt-&gt;CLOSE &nbsp; = dclose;
&gt; &nbsp;&nbsp; dt-&gt;READ&nbsp; &nbsp; = dread;
&gt; &nbsp;&nbsp; dt-&gt;WRITE &nbsp; = dwrite;
&gt; &nbsp;&nbsp; dt-&gt;LSEEK &nbsp; = dlseek;
&gt; &nbsp;&nbsp; dt-&gt;UNLINK&nbsp; = dunlink;
&gt; &nbsp;&nbsp; dt-&gt;RENAME&nbsp; = drename;
&gt; }
&gt; 
&gt; int write(int&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; fildes,
&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; const char &nbsp; *bufptr,
&gt; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; unsigned&nbsp; &nbsp; &nbsp; cnt)
&gt; {
&gt; &nbsp; 
&gt; /*------------------------------------------------------------------------*/
&gt; &nbsp;&nbsp; /* CALL FUNCTION FROM DEVICE TABLE TO PERFORM WRITE FOR THIS
&gt; DEVICE/FILE&nbsp; */
&gt; &nbsp; 
&gt; /*------------------------------------------------------------------------*/
&gt; &nbsp;&nbsp; return (*(_stream[fildes]-&gt;WRITE)) (fildes,bufptr,cnt);
&gt; }
&gt; 
&gt; &nbsp;&nbsp; Then, how can we use this runtime library together with QEMu to
&gt; implement full-stack file oerations?&nbsp; I really appreaciate any advice.

Trying to understand...

Are you trying to ask "how to implement semihosting for my
qemu-user-tidsp fork"?

Have a look at "hw/semihosting/console.h" and the implementation
(so far only ARM) of qemu_semihosting_console_[in/out].
This might help to plug read/write. Using other stream than
stdin/stdout is not supported (but you can add support) so
open/lseek/close/rename/unlink are not considered.

(for QEMU 'console' is the stdin/stdout subset of stdio).

You can redirect semihosted files with any host chardev,
this is done in qemu_semihosting_connect_chardevs().

You might also have a look at the functions declared in
"hw/semihosting/semihost.h" and how the different TCG helpers
use them.

Regards,

Phil.

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