[U-Boot] [PATCH v4 05/16] sandbox: Add a setjmp() implementation

[Simon Glass]

Hi Alex,

On 15 June 2018 at 06:01, Alexander Graf <agraf at suse.de> wrote:
>
>
> On 16.05.18 17:42, Simon Glass wrote:
>> Add an implementation of setjmp() and longjmp() which rely on the
>> underlying host C library. Since we cannot know how large the jump buffer
>> needs to be, pick something that should be suitable and check it at
>> runtime. At present we need access to the underlying struct as well.
>>
>> Signed-off-by: Simon Glass <sjg at chromium.org>
>> ---
>>
>> Changes in v4:
>> - Fix up the sizeof() operations on jmp_buf
>> - Update SPDX tags
>>
>> Changes in v3: None
>> Changes in v2: None
>>
>>  arch/sandbox/cpu/cpu.c            | 13 +++++++++++++
>>  arch/sandbox/cpu/os.c             | 23 +++++++++++++++++++++++
>>  arch/sandbox/include/asm/setjmp.h | 30 ++++++++++++++++++++++++++++++
>>  include/os.h                      | 21 +++++++++++++++++++++
>>  4 files changed, 87 insertions(+)
>>  create mode 100644 arch/sandbox/include/asm/setjmp.h
>>
>> diff --git a/arch/sandbox/cpu/cpu.c b/arch/sandbox/cpu/cpu.c
>> index d4ad020012e..cde0b055a67 100644
>> --- a/arch/sandbox/cpu/cpu.c
>> +++ b/arch/sandbox/cpu/cpu.c
>> @@ -9,6 +9,7 @@
>>  #include <linux/libfdt.h>
>>  #include <os.h>
>>  #include <asm/io.h>
>> +#include <asm/setjmp.h>
>>  #include <asm/state.h>
>>  #include <dm/root.h>
>>
>> @@ -164,3 +165,15 @@ ulong timer_get_boot_us(void)
>>
>>       return (count - base_count) / 1000;
>>  }
>> +
>> +int setjmp(jmp_buf jmp)
>> +{
>> +     return os_setjmp((ulong *)jmp, sizeof(*jmp));
>
> So, this doesn't work. Function returns increase the stack pointer which
> means after setjmp() you are not allowed to return until the longjmp
> occured. The documentation is quite clear about this:
>
>
> DESCRIPTION
>        setjmp() and longjmp(3) are useful for dealing with errors and
> interrupts encountered in a low-level subroutine of a program.  setjmp()
> saves the stack context/environment in env for later use by longjmp(3).
> The stack context will be invalidated if the function which called
> setjmp() returns.
>
>
> So we need to find a way to call setjmp() directly from the code point
> where we want to call it, rather than jump through helper functions, as
> these break its functionality.

That sounds hard but perhaps we can do something with inline
functions? It's hard because we want to call the C library in the
sandbox case. Perhaps we should rename the U-Boot version of the
function.

I wonder if in my test I just relied on hello world returning, rather
than calling the exit() function? BTW we need to find a way for
efi_selftest() to exit cleanly too. At the moment it resets.

>
> Also, os_longjmp() is broken. It calls longjmp() which however is not
> the system longjmp, but the U-Boot internal one that again calls
> os_longjmp. My quick fix was to make it call _longjmp() instead - that
> at least makes that part work.

But it hangs after that?

Regards,
Simon