Patchwork arm return

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Submitter Max Filippov
Date June 1, 2012, 12:23 p.m.
Message ID <CAMo8BfLF4AJzUetTSf2Yh2HFiPuWiW4X39Yefm6JmRktWTnPVQ@mail.gmail.com>
Download mbox | patch
Permalink /patch/162319/
State New
Headers show

Comments

Max Filippov - June 1, 2012, 12:23 p.m.
On Fri, Jun 1, 2012 at 3:57 PM, Davide Ferraretto
<femudevelopment@gmail.com> wrote:
> I tried to insert " printf("exit\n"); ", but qemu dosen't write to monitor.

printf should not write to monitor (if you mean QEMU monitor), it
should go to stdout.
I don't have ARM compiler set up ATM, but x86_64 with the following
patch does what I describe:

$ git diff

$ cat a.c
#include <stdio.h>
int main()
{
    printf("Hello, world\n");
    return 0;
}

$ gcc -static a.c -o a
$ qemu-all/root/bin/qemu-x86_64 ./a
Hello, world
TARGET_NR_exit_group

> On 06/01/12 13:43, Max Filippov wrote:
>>
>> On Fri, Jun 1, 2012 at 3:16 PM, Davide Ferraretto
>> <femudevelopment@gmail.com>  wrote:
>>>
>>> In arm user mode, where does qemu exit? Where is last qemu's instruction?
>>>
>>> I.E.
>>> int main (){return 0;}
>>> in what file does qemu run "return 0"??
>>
>> Simulated code reaches the point where libc calls 'exit' or 'exit_group'
>> syscall
>> and then QEMU goes to the do_syscall in the linux-user/syscall.c to
>> terminate
>> the process.
>>
>
Davide Ferraretto - June 1, 2012, 12:30 p.m.
I'm in "arm user space" with "sigle step mode". I want write "exit\n" in 
linux shell (no QEMU monitor) when emulate code arrives to "return 0"

On 06/01/12 14:23, Max Filippov wrote:
> On Fri, Jun 1, 2012 at 3:57 PM, Davide Ferraretto
> <femudevelopment@gmail.com>  wrote:
>> I tried to insert " printf("exit\n"); ", but qemu dosen't write to monitor.
> printf should not write to monitor (if you mean QEMU monitor), it
> should go to stdout.
> I don't have ARM compiler set up ATM, but x86_64 with the following
> patch does what I describe:
>
> $ git diff
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index 20d2a74..ccb71dc 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -5052,6 +5052,7 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
>
>       switch(num) {
>       case TARGET_NR_exit:
> +        fprintf(stderr, "TARGET_NR_exit\n");
>   #ifdef CONFIG_USE_NPTL
>         /* In old applications this may be used to implement _exit(2).
>            However in threaded applictions it is used for thread termination,
> @@ -6833,6 +6834,7 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
>   #ifdef __NR_exit_group
>           /* new thread calls */
>       case TARGET_NR_exit_group:
> +        fprintf(stderr, "TARGET_NR_exit_group\n");
>   #ifdef TARGET_GPROF
>           _mcleanup();
>   #endif
>
> $ cat a.c
> #include<stdio.h>
> int main()
> {
>      printf("Hello, world\n");
>      return 0;
> }
>
> $ gcc -static a.c -o a
> $ qemu-all/root/bin/qemu-x86_64 ./a
> Hello, world
> TARGET_NR_exit_group
>
>> On 06/01/12 13:43, Max Filippov wrote:
>>> On Fri, Jun 1, 2012 at 3:16 PM, Davide Ferraretto
>>> <femudevelopment@gmail.com>    wrote:
>>>> In arm user mode, where does qemu exit? Where is last qemu's instruction?
>>>>
>>>> I.E.
>>>> int main (){return 0;}
>>>> in what file does qemu run "return 0"??
>>> Simulated code reaches the point where libc calls 'exit' or 'exit_group'
>>> syscall
>>> and then QEMU goes to the do_syscall in the linux-user/syscall.c to
>>> terminate
>>> the process.
>>>
Max Filippov - June 1, 2012, 12:42 p.m.
On Fri, Jun 1, 2012 at 4:30 PM, Davide Ferraretto
<femudevelopment@gmail.com> wrote:
> I'm in "arm user space" with "sigle step mode". I want write "exit\n" in
> linux shell (no QEMU monitor) when emulate code arrives to "return 0"

Ok, what do you execute and where? Is it qemu-arm or qemu-system-arm?
In the latter case do you use -semihosting?

What is "ARM user space"?
How is it all related to single step mode?
Which linux shell do you mean, guest or host?

Please, don't top-post.
Max Filippov - June 1, 2012, 1:12 p.m.
On Fri, Jun 1, 2012 at 5:01 PM, Davide Ferraretto
<femudevelopment@gmail.com> wrote:
> I run qemu-arm -singlestep prog
>
> Linux shell --> host.

Ok, and you build 'prog' as a static linux ELF for ARM?
What does

qemu-arm -strace prog

print?
Max Filippov - June 1, 2012, 1:26 p.m.
On Fri, Jun 1, 2012 at 5:14 PM, Davide Ferraretto
<femudevelopment@gmail.com> wrote:
> I compile so:
> arm-elf-gcc-4.0.2 prog -o prog

As its name suggests, arm-elf-gcc builds bare-metal ELF that wouldn't
run on linux, doesn't it?
And what about the other question, what does qemu-arm -strace prog print?

Patch

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 20d2a74..ccb71dc 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -5052,6 +5052,7 @@  abi_long do_syscall(void *cpu_env, int num, abi_long arg1,

     switch(num) {
     case TARGET_NR_exit:
+        fprintf(stderr, "TARGET_NR_exit\n");
 #ifdef CONFIG_USE_NPTL
       /* In old applications this may be used to implement _exit(2).
          However in threaded applictions it is used for thread termination,
@@ -6833,6 +6834,7 @@  abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
 #ifdef __NR_exit_group
         /* new thread calls */
     case TARGET_NR_exit_group:
+        fprintf(stderr, "TARGET_NR_exit_group\n");
 #ifdef TARGET_GPROF
         _mcleanup();
 #endif